We present a first velocity map imaging study on the 234 nm photodissociation dynamics of two carbon-chain branched alkyl bromides, neopentyl bromide （denoted as NPB） and tert- pentyl bromide （denoted as TPB）. Unl...We present a first velocity map imaging study on the 234 nm photodissociation dynamics of two carbon-chain branched alkyl bromides, neopentyl bromide （denoted as NPB） and tert- pentyl bromide （denoted as TPB）. Unlike the 234 nm photodissociation of the unbranched n-C5H11Br molecule where only a direct fission of the C-Br bond is involved, the branched NPB and TPB molecules exhibit one and two more independent dissociation pathways with much energy being decayed via an extensive excitation of the bending modes of the parent molecules prior to the C-Br bond fission. This observation strongly suggests that the dissociation coordinate for the two carbon-chain branched molecules is no longer solely ascribed to the C-Br stretching mode but rather a combination of the bending-stretching modes.展开更多
We report on the photodissociation dynamics of CO2^＋ via its A2Пu,1/2 state using the scheme of [1＋1] photon excitation that is intermediated by the mode-selected A2Hu,1/2（Vl,V2,0） vibronic states. Photodissociat...We report on the photodissociation dynamics of CO2^＋ via its A2Пu,1/2 state using the scheme of [1＋1] photon excitation that is intermediated by the mode-selected A2Hu,1/2（Vl,V2,0） vibronic states. Photodissociation fragment exciation spectrum and images of photofragment CO＋ have been measured to obtain reaction dynamics parameters such as the available energy and the average translational energy. Combining with the potential energy functions of CO2^＋, the dissociation mechanism of CO2^＋ is discussed. The conformational variation of CO2^＋ from linear to bent on the photodissociation dynamics of CO2^＋ is verified.展开更多
We report a newly constructed laser ablation crossed molecular beam apparatus, equipped with time-sliced velocity map imaging technique, to study state-to-state metal atom reaction dynamics. Supersonic metal atomic be...We report a newly constructed laser ablation crossed molecular beam apparatus, equipped with time-sliced velocity map imaging technique, to study state-to-state metal atom reaction dynamics. Supersonic metal atomic beam is generated by laser vaporization of metal rod, and free expansion design without gas flow channel has been employed to obtain a good quality of metal atomic beam. We have chosen the crossed-beam reaction Al＋O2 to test the performance of the new apparatus. Two-rotational-states selected AIO（X^2∑＋, v=0, N and N＋I4） products can be imaged via P（N） and R（N＋14） branches of the Av=l band at the same wavelength, during （1＋1） resonance-enhanced multi-photon ionization through the AIO（D2E＋） intermediate state. In our experiment at 244.145 nm for simultaneous transitions of P（15） and R（29） branch, two rings in slice image were clearly distinguishable, corresponding to the AiO（v=0, N=IS） and AIO（v=0, N=29） states respectively. The energy difference between the two rotational levels is 403 cm^-1. The success of two states resolved in our apparatus suggests a better collisional energy resolution compared with the recent research study [J. Chem. Phys. 140, 214304 （2014）].展开更多
Photodissociation dynamics of dichlorodifluoromethane (CF2Cl2) around 235 nm has been studied using the time-sliced velocity map imaging technology in combination with the resonance enhanced multi-photon ionization te...Photodissociation dynamics of dichlorodifluoromethane (CF2Cl2) around 235 nm has been studied using the time-sliced velocity map imaging technology in combination with the resonance enhanced multi-photon ionization technology. By measuring the raw images of chlorine atoms which are formed via one-photon dissociation of CF2Cl2, the speed and angular distributions can be directly obtained. The speed distribution of excited-state chlorine atoms consists of high translation energy (ET) and low ET components, which are related to direct dissociation on 3Q0 state and predissociation on the ground state induced by internal conversion, respectively. The speed distribution of ground-state chlorine atoms also consists of high ET and low ET components which are related to predissociation between 3Q0 and 1Q1 states and predissociation on the ground state induced by internal conversion, respectively. Radical dissociation channel is confirmed, nevertheless, secondary dissociation and three-body dissociation channels are excluded.展开更多
We investigate the influence of the interaction volume on the energy resolution of a velocity map imaging spectrometer. The simulation results show that the axial interaction size has a significant influence on the re...We investigate the influence of the interaction volume on the energy resolution of a velocity map imaging spectrometer. The simulation results show that the axial interaction size has a significant influence on the resolution. This influence is increased for a higher kinetic energy. We further show that the radial interaction size has a minor influence on the energy resolution for the electron or ion with medium energy, but it is crucial for the resolution of the electron or ion With low kinetic energy. By tracing the flight trajectories we show how the electron or ion energy resolution is influenced by the interaction size.展开更多
The photodissociation dynamics of acetaldehyde in the radical channel CH3＋HCO has been reinvestigated using time-sliced velocity map imaging technique in the photolysis wavelength range of 275-321 nm. The CH3 fragmen...The photodissociation dynamics of acetaldehyde in the radical channel CH3＋HCO has been reinvestigated using time-sliced velocity map imaging technique in the photolysis wavelength range of 275-321 nm. The CH3 fragments have been probed via （2＋1） resonance-enhanced multiphoton ionization. Images are measured for CH3 formed in the ground and excited states （v2=0 and 1） of the umbrella vibrational mode. For acetaldehyde dissociation on T1 state after intersystem crossing from S1 state, the products are formed with high translational energy release and low internal excitation. The rotational and vibrational energy of both fragments increases with increasing photodissociation energy. The triplet barrier height is estimated at 3.8814-0.006 eV above the ground state of acetaldehyde.展开更多
Measurement of oxygen concentration and distribution in brain is essential to understanding the pathophysiology of stroke. Although brain oxygen level is critical for brain tissue survival,
The photodissociation dynamics of isocyanic acid （HNCO） has been studied by the time- sliced velocity map ion imaging technique at 193 nm. The NH（a1△） products were measured via （2＋1） resonance enhanced multip...The photodissociation dynamics of isocyanic acid （HNCO） has been studied by the time- sliced velocity map ion imaging technique at 193 nm. The NH（a1△） products were measured via （2＋1） resonance enhanced multiphoton ionization. Images have been accumulated for the NH（a1△） rotational states in the ground and vibrational excited state （v=0 and 1）. The center-of-mass translational energy distribution derived from the NH（a1△） images implies that the CO vibrational distributions are inverted for most of the measured 1NH（v｜j） internal states. The anisotropic product angular distribution observed indicates a rapid dissociation process for the N-C bond cleavage. A bimodal rotational state distribution of CO（v） has been observed, this result implies that isocyanic acid dissociates in the S1 state in two different pathways.展开更多
An improved topographic database for King George Island,one of the most frequently visited regions in Antarctica,is presented.A first step consisted in combining data from differential GPS surveys gained during the au...An improved topographic database for King George Island,one of the most frequently visited regions in Antarctica,is presented.A first step consisted in combining data from differential GPS surveys gained during the austral summers 1997～1998 and 1999～2000,with the current coastline from a SPOT satellite image mosaic,topographic information from existing maps and from the Antarctic Digital Database.From this data sets,a digital terrain model (DTM) was generated using Arc/Info GIS.In a second step,a satellite image map at the scale 1∶100 000 was assembled from contour lines derived from the DTM and the satellite mosaic.A lack of accurate topographic information in the eastern part of the island was identified.Additional topographic surveying or SAR interferometry should be used to improve the data quality in that area.The GIS integrated database will be indispensable for glaciological and climatological studies and administrative and scientific purposes.In future,the application of GIS techniques will be mandatory for environmental impact studies and environmental monitoring as well as for management plans on King George Island.展开更多
Gully feature mapping is an indispensable prerequisite for the motioning and control of gully erosion which is a widespread natural hazard. The increasing availability of high-resolution Digital Elevation Model(DEM) a...Gully feature mapping is an indispensable prerequisite for the motioning and control of gully erosion which is a widespread natural hazard. The increasing availability of high-resolution Digital Elevation Model(DEM) and remote sensing imagery, combined with developed object-based methods enables automatic gully feature mapping. But still few studies have specifically focused on gully feature mapping on different scales. In this study, an object-based approach to two-level gully feature mapping, including gully-affected areas and bank gullies, was developed and tested on 1-m DEM and Worldview-3 imagery of a catchment in the Chinese Loess Plateau. The methodology includes a sequence of data preparation, image segmentation, metric calculation, and random forest based classification. The results of the two-level mapping were based on a random forest model after investigating the effects of feature selection and class-imbalance problem. Results show that the segmentation strategy adopted in this paper which considers the topographic information and optimal parameter combination can improve the segmentation results. The distribution of the gully-affected area is closely related to topographic information, however, the spectral features are more dominant for bank gully mapping. The highest overall accuracy of the gully-affected area mapping was 93.06% with four topographic features. The highest overall accuracy of bank gully mapping is 78.5% when all features are adopted. The proposed approach is a creditable option for hierarchical mapping of gully feature information, which is suitable for the application in hily Loess Plateau region.展开更多
The ionization processes of NH3 molecule are studied by photoelectron velocity map imaging technique in a linearly polarized 400-nm femtosecond laser field. The two-dimensional photoelectron images from ammonia molecu...The ionization processes of NH3 molecule are studied by photoelectron velocity map imaging technique in a linearly polarized 400-nm femtosecond laser field. The two-dimensional photoelectron images from ammonia molecules under different laser intensities are obtained. In the slow electron region, the values of kinetic energy of photoelectrons corresponding to peaks 1, 2, 3, and 4 are 0.27, 0.86, 1.16, and 1.6 eV, respectively. With both the kinetic energy and angular distribution of photoelectrons from NH3 molecules, we can confirm that the two-photon excited intermediate Rydberg state is A^1 A2" (v2'=3) state for photoelectron peaks 2, 3, 4, and the three peaks are marked as 1223 (2 + 2), 1123 (2 + 2), and 1023 (2 + 2) multi-photon processes, respectively. Then, peak 1 is found by adding a hexapole between the source chamber and the detection chamber to realize the rotational state selection and beam focusing. Peak 1 is labeled as the 1323 (3 + 1) multi-photon process through the intermediate Rydberg state E^1A1'. The phenomena of channel switching are found in the slow electron kinetic energy distributions. Our calculations and experimental results indicate that the stretching vibrational mode of ammonia molecules varies with channels, while the umbrella vibration does not. In addition, we consider and discuss the ac-Stark effect in a strong laser field. Peaks 5 and 6 are marked as (2 + 2 + 1) and (2 + 2 + 2) above threshold ionization processes in the fast electron region.展开更多
The ultrafast dissociation dynamics of NO2 molecules was investigated by femtosecond laser pump-probe mass spectra and ion images.The results show that the kinetic energy release of NO+ions has two components,0.05 eV ...The ultrafast dissociation dynamics of NO2 molecules was investigated by femtosecond laser pump-probe mass spectra and ion images.The results show that the kinetic energy release of NO+ions has two components,0.05 eV and 0.25 eV,and the possible dissociation channels have been assigned.The channel resolved transient measurement of NO^+provides a method to disentangle the contribution of ultrafast dissociation pathways,and the transient curves of NO^+ions at different kinetic energy release are fitted by a biexponential function.The fast component with a decay time of 0.25 ps is generated from the evolution of Rydberg states.The slow component is generated from two competitive channels,one of the channel is absorbing one 400nm photon to the excited state A^2B2,which has a decay time of 30.0ps,and the other slow channel is absorbing three 400nm photons to valence type Rydberg states which have a decay time less than 7.2ps.The channel and time resolved experiment present the potential of sorting out the complex ultrafast dissociation dynamics of molecules.展开更多
Dissociative charge exchange re-actions between Ar^(+)ion and trans-/cis-dichloroethylene(trans-/cis-C_(2)H_(2)Cl_(2))are investi-gated with the ion-velocity imag-ing technique.The dechlorinated product C_(2)H_(2)Cl^(...Dissociative charge exchange re-actions between Ar^(+)ion and trans-/cis-dichloroethylene(trans-/cis-C_(2)H_(2)Cl_(2))are investi-gated with the ion-velocity imag-ing technique.The dechlorinated product C_(2)H_(2)Cl^(+)is the predomi-nant,and most of this product show the spatial distribution around the target,implying that the dissociation occurs in the large impact-parameter collision and via the energy resonant charge transfer.Meanwhile,a few C_(2)H_(2)Cl^(+)locate around the center-of-mass,which is at-tributed to the fragmentation of intimate association between C_(2)H_(2)Cl_(2)and Ar^(+)or in the small impact-parameter collision.The product C_(2)HCl_(+)exhibits the velocity distribution fea-tures similar to those of C_(2)H_(2)Cl_(+).The rarest product C_(2)HCl_(2)+shows the distributions around the molecular target,due to the quick dehydrogenation after the energy-resonant charge transfer in the large impact-parameter collision.展开更多
The NH(a^1Δ)+CO(X^1Σ+) product channel for the photodissociation of isocyanic acid(HNCO) on the first excited singlet state S1 has been investigated by means of time-sliced ionvelocity map imaging technique at photo...The NH(a^1Δ)+CO(X^1Σ+) product channel for the photodissociation of isocyanic acid(HNCO) on the first excited singlet state S1 has been investigated by means of time-sliced ionvelocity map imaging technique at photolysis wavelengths around 201 nm. The CO productwas detected through (2+1) resonance enhanced multiphoton ionization (REMPI). Imageswere obtained for CO products formed in the ground and vibrational excited state (v=0 and v=1). The energy distributions and product angular distributions were obtained from the CO velocity imaging. The correlated NH(a^1Δ) rovibrational state distributions were determined.The vibrational branching ratio of 1NH (v=1/v=0) increases as the rotational state of CO(v=0) increases initially and decreases afterwards, which indicates a special state-tostate correlation between the 1NH and CO products. About half of the available energy was partitioned into the translational degree of freedom. The negative anisotropy parameter indicates that it is a vertical direct dissociation process.展开更多
The recen tly cons true ted cryogenic cylindrical ion trap velocity map imaging spectrometer(CIT-VMI)has been upgraded for coincidence imaging of both ionic and neutral photofragments from photodissociation of ionic s...The recen tly cons true ted cryogenic cylindrical ion trap velocity map imaging spectrometer(CIT-VMI)has been upgraded for coincidence imaging of both ionic and neutral photofragments from photodissociation of ionic species.The prepared ions are cooled down in a homemade cryogenic cylindrical ion trap and then extracted for photodissociation experiments.Wi th the newly designed elec trie fields for extraction and acceleration,the ion beam can be accelerated to more than 4500 eV,which is necessary for velocity imaging of the neutral photofragments by using the position-sensitive imaging detect or.The setup has been tested by the 355 nm pho todissocia tion dynamics of the argon dimer cat ion(Ar2+).From the recorded experimen tal images of both neu tral Ar and ionic Ar+fragments,we interpret velocity resolutions of△v/vu4.6%for neutral fragments,and△v/vul.5%for ionic fragments,respectively.展开更多
The reaction dynamics of yttrium atoms with sulfur dioxide molecules at a high collision energy of 36 kcal/mol was studied using time-sliced velocity map ion imaging,crossed molecular beam and laser-ablation method.Th...The reaction dynamics of yttrium atoms with sulfur dioxide molecules at a high collision energy of 36 kcal/mol was studied using time-sliced velocity map ion imaging,crossed molecular beam and laser-ablation method.The product YO was detected via multiphoton ionization at various wavelengths in the region of 482-615 nm.The slice images of YO show a broad velocity distribution and forward-backward peaking angular distribution.The forward scattering signal is stronger than its backward distribution.This indicates that the reaction proceeds via an intermediate complex and the lifetime of the intermediate state is less than one rotational period.The formation of complex suggests that electron transfer occurs in the oxidation reaction.展开更多
The[1+1]two-photon dissociation dynamics of mass-selected 79 Br_(2)^(+)has been studied in a cold ion beam using a cryogenic cylindrical ion trap velocity map imaging spectrometer.The quartet 14Σ-u;3=2 state of 79Br2...The[1+1]two-photon dissociation dynamics of mass-selected 79 Br_(2)^(+)has been studied in a cold ion beam using a cryogenic cylindrical ion trap velocity map imaging spectrometer.The quartet 14Σ-u;3=2 state of 79Br2+is employed as an intermediate state to initiate resonance enhanced two-photon excitation to high-lying dissociative states in the 4.0-5.0 eV energy region above the ground rovibronic state.Total kinetic energy release(TKER)and the twodimensional recoiling velocity distributions of fragmented 79Br+ions are measured using the technique of DC-slice velocity map imaging.Branching ratios for individual state-resolved product channels are determined from the TKER spectra.The measured photofragment angular distributions indicate that the dissociation of 79Br2+occurs in dissociativeΩ=3/2 state viaΔΩ=0 parallel transition from the 14Σ-u;3=2 intermediate state.Due to the considerable spin-orbit coupling effects in the excited states of 79Br2+,higher-lying dissociative quartet states are likely responsible for the observed photodissociation processes.展开更多
We study the H＋CH4/CD4-＋H2/HD＋CH3/CD3 reactions using the time sliced velocity map ion imaging technique. Ion images of the CH3/CD3 products were measured by the （2＋1） resonance enhanced multi-photon ionization ...We study the H＋CH4/CD4-＋H2/HD＋CH3/CD3 reactions using the time sliced velocity map ion imaging technique. Ion images of the CH3/CD3 products were measured by the （2＋1） resonance enhanced multi-photon ionization （REMPI） detection method. Besides the CH3/CD3 products in the ground state, ion images of the vibrationally excited CH3/CD3 products were also observed at two collision energies of 0.72 and 1.06 eV. It is shown that the angular distribution of the products CH3/CD3 in vibrationally excited states gradually vary from backward scattering to sideways scattering as the collision energy increases. Compared to the CH3/CD3 products in the ground state, the CH3/CD3 products in vibrationally excited states tend to be more sideways scattered, indicating that larger impact parameters play a more important role in the vibrationally excited product channels.展开更多
Our experimental progresses on the reaction dynamics of dissociative electron attachment(DEA)to carbon dioxide(CO2)are summarized in this review.First,we introduce some fundamentals about the DEA dynamics and provide ...Our experimental progresses on the reaction dynamics of dissociative electron attachment(DEA)to carbon dioxide(CO2)are summarized in this review.First,we introduce some fundamentals about the DEA dynamics and provide an epitome about the DEAs to CO2.Second,the experimental technique developments are described,in particular,on the highresolution velocity map imaging apparatus in which we put a lot of efforts during the past two years.Third,our findings about the DEA dynamics of CO2 are surveyed and briefly compared with the others’work.At last,we give a perspective about the applications of the DEA studies and highlight the inspirations in the production of molecular oxygen on Mars and the catalytic transformations of CO2.展开更多
基金This work was supported by the National Natural Science Foundation of China （No.20873133）, the Ministry of Science and Technology of China （No.2007CB815203 and No.2010CB923302）, the Chinese Academy of Sciences （No.KJCX2-YW-N24 and No.KJCX2-EW-W09）, the Fundamental Research Funds for the Central Universities of China （No.WK2340000012）, and the USTC-NSRL Joint Funds （No.KY2340000021）.
文摘We present a first velocity map imaging study on the 234 nm photodissociation dynamics of two carbon-chain branched alkyl bromides, neopentyl bromide （denoted as NPB） and tert- pentyl bromide （denoted as TPB）. Unlike the 234 nm photodissociation of the unbranched n-C5H11Br molecule where only a direct fission of the C-Br bond is involved, the branched NPB and TPB molecules exhibit one and two more independent dissociation pathways with much energy being decayed via an extensive excitation of the bending modes of the parent molecules prior to the C-Br bond fission. This observation strongly suggests that the dissociation coordinate for the two carbon-chain branched molecules is no longer solely ascribed to the C-Br stretching mode but rather a combination of the bending-stretching modes.
基金This work was supported by the Natural Science Foundation of Changzhou Institute of Technology （No.YN1507）, Undergraduate Training Program for Innovation of Changzhou Institute of Technology （No.J150245）, the China Postdoctoral Science Foundation （No.2013M531506）, the National Natural Science Foundation of China （No.21273212）.
文摘We report on the photodissociation dynamics of CO2^＋ via its A2Пu,1/2 state using the scheme of [1＋1] photon excitation that is intermediated by the mode-selected A2Hu,1/2（Vl,V2,0） vibronic states. Photodissociation fragment exciation spectrum and images of photofragment CO＋ have been measured to obtain reaction dynamics parameters such as the available energy and the average translational energy. Combining with the potential energy functions of CO2^＋, the dissociation mechanism of CO2^＋ is discussed. The conformational variation of CO2^＋ from linear to bent on the photodissociation dynamics of CO2^＋ is verified.
基金We are indebted to Prof. Kopin Liu （IAMS, Taipei） for stimulating discussions on going experiments, to Prof. Ming-fei Zhou and Assoc. Prof. Guan-jun Wang （Fudan University, Shanghai） for assistance in building machine, to Prof. Uzi. Even （Tel Aviv University, Tel Aviv） for discussions oil E1 valve employnmnt in laser ablation, and to Prof. Xue-ming Yang＇s group （DICP, Dalian） for new Iaser system. This work was supported by the National Natural Science Foundation of China （No.21322309） and the Program for Professor of Special Appointment （Eastern Scholar） at Shanghai Institutions of Higher Learning.
文摘We report a newly constructed laser ablation crossed molecular beam apparatus, equipped with time-sliced velocity map imaging technique, to study state-to-state metal atom reaction dynamics. Supersonic metal atomic beam is generated by laser vaporization of metal rod, and free expansion design without gas flow channel has been employed to obtain a good quality of metal atomic beam. We have chosen the crossed-beam reaction Al＋O2 to test the performance of the new apparatus. Two-rotational-states selected AIO（X^2∑＋, v=0, N and N＋I4） products can be imaged via P（N） and R（N＋14） branches of the Av=l band at the same wavelength, during （1＋1） resonance-enhanced multi-photon ionization through the AIO（D2E＋） intermediate state. In our experiment at 244.145 nm for simultaneous transitions of P（15） and R（29） branch, two rings in slice image were clearly distinguishable, corresponding to the AiO（v=0, N=IS） and AIO（v=0, N=29） states respectively. The energy difference between the two rotational levels is 403 cm^-1. The success of two states resolved in our apparatus suggests a better collisional energy resolution compared with the recent research study [J. Chem. Phys. 140, 214304 （2014）].
基金supported by the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (No.17KJB150005 and No.17KJD510001)the Natural Science Foundation of Changzhou Institute of Technology (No.YN1507 and No.YN1611)+1 种基金Undergraduate Training Program for Innovation of Changzhou Institute of Technology (No.2017276Y)the National Natural Science Foundation of China (No.21273212)
文摘Photodissociation dynamics of dichlorodifluoromethane (CF2Cl2) around 235 nm has been studied using the time-sliced velocity map imaging technology in combination with the resonance enhanced multi-photon ionization technology. By measuring the raw images of chlorine atoms which are formed via one-photon dissociation of CF2Cl2, the speed and angular distributions can be directly obtained. The speed distribution of excited-state chlorine atoms consists of high translation energy (ET) and low ET components, which are related to direct dissociation on 3Q0 state and predissociation on the ground state induced by internal conversion, respectively. The speed distribution of ground-state chlorine atoms also consists of high ET and low ET components which are related to predissociation between 3Q0 and 1Q1 states and predissociation on the ground state induced by internal conversion, respectively. Radical dissociation channel is confirmed, nevertheless, secondary dissociation and three-body dissociation channels are excluded.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11234004 and 61275126)
文摘We investigate the influence of the interaction volume on the energy resolution of a velocity map imaging spectrometer. The simulation results show that the axial interaction size has a significant influence on the resolution. This influence is increased for a higher kinetic energy. We further show that the radial interaction size has a minor influence on the energy resolution for the electron or ion with medium energy, but it is crucial for the resolution of the electron or ion With low kinetic energy. By tracing the flight trajectories we show how the electron or ion energy resolution is influenced by the interaction size.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.21203186 and No.21073187）, the National Key Basic Research Program of China （No.2010CB923302）, 100 Talents Program of Chinese Academy of Sciences, and Knowledge Innovation Program of Chinese Academy of Sciences.
文摘The photodissociation dynamics of acetaldehyde in the radical channel CH3＋HCO has been reinvestigated using time-sliced velocity map imaging technique in the photolysis wavelength range of 275-321 nm. The CH3 fragments have been probed via （2＋1） resonance-enhanced multiphoton ionization. Images are measured for CH3 formed in the ground and excited states （v2=0 and 1） of the umbrella vibrational mode. For acetaldehyde dissociation on T1 state after intersystem crossing from S1 state, the products are formed with high translational energy release and low internal excitation. The rotational and vibrational energy of both fragments increases with increasing photodissociation energy. The triplet barrier height is estimated at 3.8814-0.006 eV above the ground state of acetaldehyde.
文摘Measurement of oxygen concentration and distribution in brain is essential to understanding the pathophysiology of stroke. Although brain oxygen level is critical for brain tissue survival,
基金supported by the National Natural Science Foundation of China(No.21573227,N0.11604052)the National Science Foundation of Anhui Province of China(No.1608085QA19)+2 种基金the Natural Science Research Project of Education Department of Anhui Province of China(No.2014KJ020)the Open Foundation of State Key Laboratory(No.SKLMRDK201503,No.SKLMRD-K201611,and No.SKLMRDK201711)the Doctoral Foundation of Fuyang Normal University(No.FSB201501005)
文摘The photodissociation dynamics of isocyanic acid （HNCO） has been studied by the time- sliced velocity map ion imaging technique at 193 nm. The NH（a1△） products were measured via （2＋1） resonance enhanced multiphoton ionization. Images have been accumulated for the NH（a1△） rotational states in the ground and vibrational excited state （v=0 and 1）. The center-of-mass translational energy distribution derived from the NH（a1△） images implies that the CO vibrational distributions are inverted for most of the measured 1NH（v｜j） internal states. The anisotropic product angular distribution observed indicates a rapid dissociation process for the N-C bond cleavage. A bimodal rotational state distribution of CO（v） has been observed, this result implies that isocyanic acid dissociates in the S1 state in two different pathways.
文摘An improved topographic database for King George Island,one of the most frequently visited regions in Antarctica,is presented.A first step consisted in combining data from differential GPS surveys gained during the austral summers 1997～1998 and 1999～2000,with the current coastline from a SPOT satellite image mosaic,topographic information from existing maps and from the Antarctic Digital Database.From this data sets,a digital terrain model (DTM) was generated using Arc/Info GIS.In a second step,a satellite image map at the scale 1∶100 000 was assembled from contour lines derived from the DTM and the satellite mosaic.A lack of accurate topographic information in the eastern part of the island was identified.Additional topographic surveying or SAR interferometry should be used to improve the data quality in that area.The GIS integrated database will be indispensable for glaciological and climatological studies and administrative and scientific purposes.In future,the application of GIS techniques will be mandatory for environmental impact studies and environmental monitoring as well as for management plans on King George Island.
基金Under the auspices of Priority Academic Program Development of Jiangsu Higher Education Institutions,National Natural Science Foundation of China(No.41271438,41471316,41401440,41671389)
文摘Gully feature mapping is an indispensable prerequisite for the motioning and control of gully erosion which is a widespread natural hazard. The increasing availability of high-resolution Digital Elevation Model(DEM) and remote sensing imagery, combined with developed object-based methods enables automatic gully feature mapping. But still few studies have specifically focused on gully feature mapping on different scales. In this study, an object-based approach to two-level gully feature mapping, including gully-affected areas and bank gullies, was developed and tested on 1-m DEM and Worldview-3 imagery of a catchment in the Chinese Loess Plateau. The methodology includes a sequence of data preparation, image segmentation, metric calculation, and random forest based classification. The results of the two-level mapping were based on a random forest model after investigating the effects of feature selection and class-imbalance problem. Results show that the segmentation strategy adopted in this paper which considers the topographic information and optimal parameter combination can improve the segmentation results. The distribution of the gully-affected area is closely related to topographic information, however, the spectral features are more dominant for bank gully mapping. The highest overall accuracy of the gully-affected area mapping was 93.06% with four topographic features. The highest overall accuracy of bank gully mapping is 78.5% when all features are adopted. The proposed approach is a creditable option for hierarchical mapping of gully feature information, which is suitable for the application in hily Loess Plateau region.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11574116, 11534004, and 10704028).
文摘The ionization processes of NH3 molecule are studied by photoelectron velocity map imaging technique in a linearly polarized 400-nm femtosecond laser field. The two-dimensional photoelectron images from ammonia molecules under different laser intensities are obtained. In the slow electron region, the values of kinetic energy of photoelectrons corresponding to peaks 1, 2, 3, and 4 are 0.27, 0.86, 1.16, and 1.6 eV, respectively. With both the kinetic energy and angular distribution of photoelectrons from NH3 molecules, we can confirm that the two-photon excited intermediate Rydberg state is A^1 A2" (v2'=3) state for photoelectron peaks 2, 3, 4, and the three peaks are marked as 1223 (2 + 2), 1123 (2 + 2), and 1023 (2 + 2) multi-photon processes, respectively. Then, peak 1 is found by adding a hexapole between the source chamber and the detection chamber to realize the rotational state selection and beam focusing. Peak 1 is labeled as the 1323 (3 + 1) multi-photon process through the intermediate Rydberg state E^1A1'. The phenomena of channel switching are found in the slow electron kinetic energy distributions. Our calculations and experimental results indicate that the stretching vibrational mode of ammonia molecules varies with channels, while the umbrella vibration does not. In addition, we consider and discuss the ac-Stark effect in a strong laser field. Peaks 5 and 6 are marked as (2 + 2 + 1) and (2 + 2 + 2) above threshold ionization processes in the fast electron region.
基金supported by the National Natural Science Foundation of China(No.11704148,No.11847039,No.11534004)
文摘The ultrafast dissociation dynamics of NO2 molecules was investigated by femtosecond laser pump-probe mass spectra and ion images.The results show that the kinetic energy release of NO+ions has two components,0.05 eV and 0.25 eV,and the possible dissociation channels have been assigned.The channel resolved transient measurement of NO^+provides a method to disentangle the contribution of ultrafast dissociation pathways,and the transient curves of NO^+ions at different kinetic energy release are fitted by a biexponential function.The fast component with a decay time of 0.25 ps is generated from the evolution of Rydberg states.The slow component is generated from two competitive channels,one of the channel is absorbing one 400nm photon to the excited state A^2B2,which has a decay time of 30.0ps,and the other slow channel is absorbing three 400nm photons to valence type Rydberg states which have a decay time less than 7.2ps.The channel and time resolved experiment present the potential of sorting out the complex ultrafast dissociation dynamics of molecules.
基金supported by the National Natural Sci-ence Foundation of China(No.22003062 and No.21625301)the Chinese Academy of Sciences(No.YZ201565).
文摘Dissociative charge exchange re-actions between Ar^(+)ion and trans-/cis-dichloroethylene(trans-/cis-C_(2)H_(2)Cl_(2))are investi-gated with the ion-velocity imag-ing technique.The dechlorinated product C_(2)H_(2)Cl^(+)is the predomi-nant,and most of this product show the spatial distribution around the target,implying that the dissociation occurs in the large impact-parameter collision and via the energy resonant charge transfer.Meanwhile,a few C_(2)H_(2)Cl^(+)locate around the center-of-mass,which is at-tributed to the fragmentation of intimate association between C_(2)H_(2)Cl_(2)and Ar^(+)or in the small impact-parameter collision.The product C_(2)HCl_(+)exhibits the velocity distribution fea-tures similar to those of C_(2)H_(2)Cl_(+).The rarest product C_(2)HCl_(2)+shows the distributions around the molecular target,due to the quick dehydrogenation after the energy-resonant charge transfer in the large impact-parameter collision.
基金supported by the National Science Foundation of Anhui Province(No.1608085QA19)the National Science Foundation of China(No.11604052)+3 种基金the Natural Science Research Project of Education Department of Anhui Province(No.2014KJ020)the PhD Research Startup Foundation of Fuyang Normal University(No.FSB201501005)the Quality Engineering Project of Anhui Province(No.2017jyxm0277)the Open Foundation of State Key Laboratory(Nos.SKLMRD-K201611,SKLMRD-K201711 and SKLMRD-K201810)
文摘The NH(a^1Δ)+CO(X^1Σ+) product channel for the photodissociation of isocyanic acid(HNCO) on the first excited singlet state S1 has been investigated by means of time-sliced ionvelocity map imaging technique at photolysis wavelengths around 201 nm. The CO productwas detected through (2+1) resonance enhanced multiphoton ionization (REMPI). Imageswere obtained for CO products formed in the ground and vibrational excited state (v=0 and v=1). The energy distributions and product angular distributions were obtained from the CO velocity imaging. The correlated NH(a^1Δ) rovibrational state distributions were determined.The vibrational branching ratio of 1NH (v=1/v=0) increases as the rotational state of CO(v=0) increases initially and decreases afterwards, which indicates a special state-tostate correlation between the 1NH and CO products. About half of the available energy was partitioned into the translational degree of freedom. The negative anisotropy parameter indicates that it is a vertical direct dissociation process.
基金This work was supported by the National Key R&D Program of China(No.2017YFA0303502)the National Natural Science Foundation of China(No.21773221 and No.21827804)the Fundamental Research Funds for the Central Universities of China(No.WK2340000078).
文摘The recen tly cons true ted cryogenic cylindrical ion trap velocity map imaging spectrometer(CIT-VMI)has been upgraded for coincidence imaging of both ionic and neutral photofragments from photodissociation of ionic species.The prepared ions are cooled down in a homemade cryogenic cylindrical ion trap and then extracted for photodissociation experiments.Wi th the newly designed elec trie fields for extraction and acceleration,the ion beam can be accelerated to more than 4500 eV,which is necessary for velocity imaging of the neutral photofragments by using the position-sensitive imaging detect or.The setup has been tested by the 355 nm pho todissocia tion dynamics of the argon dimer cat ion(Ar2+).From the recorded experimen tal images of both neu tral Ar and ionic Ar+fragments,we interpret velocity resolutions of△v/vu4.6%for neutral fragments,and△v/vul.5%for ionic fragments,respectively.
基金supported by the National Natural Science Foundation of China (No.21673047,No.21327901and No.21573047)the Shanghai Key Laboratory Foundation of Molecular Catalysis and Innovative Materialsthe Program for Professor of Special Appointment(Eastern Scholar) at Shanghai Institutions of Higher Learning.
文摘The reaction dynamics of yttrium atoms with sulfur dioxide molecules at a high collision energy of 36 kcal/mol was studied using time-sliced velocity map ion imaging,crossed molecular beam and laser-ablation method.The product YO was detected via multiphoton ionization at various wavelengths in the region of 482-615 nm.The slice images of YO show a broad velocity distribution and forward-backward peaking angular distribution.The forward scattering signal is stronger than its backward distribution.This indicates that the reaction proceeds via an intermediate complex and the lifetime of the intermediate state is less than one rotational period.The formation of complex suggests that electron transfer occurs in the oxidation reaction.
基金the National Natural Science Foundation of China(No.21773221 and No.21827804),the National Key R&D Program of China(2017YFA0303502),and Fundamental Research Funds for the Central Universities of China(WK2340000078).
文摘The[1+1]two-photon dissociation dynamics of mass-selected 79 Br_(2)^(+)has been studied in a cold ion beam using a cryogenic cylindrical ion trap velocity map imaging spectrometer.The quartet 14Σ-u;3=2 state of 79Br2+is employed as an intermediate state to initiate resonance enhanced two-photon excitation to high-lying dissociative states in the 4.0-5.0 eV energy region above the ground rovibronic state.Total kinetic energy release(TKER)and the twodimensional recoiling velocity distributions of fragmented 79Br+ions are measured using the technique of DC-slice velocity map imaging.Branching ratios for individual state-resolved product channels are determined from the TKER spectra.The measured photofragment angular distributions indicate that the dissociation of 79Br2+occurs in dissociativeΩ=3/2 state viaΔΩ=0 parallel transition from the 14Σ-u;3=2 intermediate state.Due to the considerable spin-orbit coupling effects in the excited states of 79Br2+,higher-lying dissociative quartet states are likely responsible for the observed photodissociation processes.
文摘We study the H＋CH4/CD4-＋H2/HD＋CH3/CD3 reactions using the time sliced velocity map ion imaging technique. Ion images of the CH3/CD3 products were measured by the （2＋1） resonance enhanced multi-photon ionization （REMPI） detection method. Besides the CH3/CD3 products in the ground state, ion images of the vibrationally excited CH3/CD3 products were also observed at two collision energies of 0.72 and 1.06 eV. It is shown that the angular distribution of the products CH3/CD3 in vibrationally excited states gradually vary from backward scattering to sideways scattering as the collision energy increases. Compared to the CH3/CD3 products in the ground state, the CH3/CD3 products in vibrationally excited states tend to be more sideways scattered, indicating that larger impact parameters play a more important role in the vibrationally excited product channels.
基金supported by the National Natural Science Foundation of China(No.21727804,No.21625301,No.21273213)。
文摘Our experimental progresses on the reaction dynamics of dissociative electron attachment(DEA)to carbon dioxide(CO2)are summarized in this review.First,we introduce some fundamentals about the DEA dynamics and provide an epitome about the DEAs to CO2.Second,the experimental technique developments are described,in particular,on the highresolution velocity map imaging apparatus in which we put a lot of efforts during the past two years.Third,our findings about the DEA dynamics of CO2 are surveyed and briefly compared with the others’work.At last,we give a perspective about the applications of the DEA studies and highlight the inspirations in the production of molecular oxygen on Mars and the catalytic transformations of CO2.
