The evolution of a molecular system excited above its ionization threshold depends on a number of parameters that include the nature of the excited states and their couplings to the various continua. The general natur...The evolution of a molecular system excited above its ionization threshold depends on a number of parameters that include the nature of the excited states and their couplings to the various continua. The general nature of the processes governing this evolution depends also essentially on the complexity of the molecule, more precisely on its size, density of states, and strength of the couplings among the various internal degrees of freedom. In this paper we address the question of the transition between autoionization that prevails in small molecules, and delayed ionization occurring in larger molecules or clusters. This transition is illustrated by autoionization of Na2 Rydberg states on one hand, delayed ionization in fullerene C60, and delayed detachment in small cluster anions on the other hand. All processes are studied in the case of nanosecond laser excitation, corresponding to a rather slow deposition of the internal energy.展开更多
Full quantum mechanical calculations are performed to determine the broadening in the far wings of the cesium D1 and D2 line shapes arising from elastic collisions of Cs atom with inert helium atoms. The potential ene...Full quantum mechanical calculations are performed to determine the broadening in the far wings of the cesium D1 and D2 line shapes arising from elastic collisions of Cs atom with inert helium atoms. The potential energy curves of the low-lying CsHe molecular states, as well as the related transition dipole moments, are carefully computed from ab initio methods based on state-averaged complete active space self-consistent field-multireference configuration interaction(SACASSCF-MRCI) calculations, involving the spin-orbit effect, and taking into account the Davidson and BSSE corrections.The absorption and emission reduced coefficients are determined in the temperature and wavelength ranges of 323-3000 K and 800-1000 nm, respectively. Both profiles of the absorption and the emission are dominated by the free-free transitions,and exhibit a satellite peak in the blue wing near the wavelength 825 nm, attributed to B^2Σ1/2^+→ X^2Σ1/2^+/transitions. The results are in good agreement with previous experimental and theoretical works.展开更多
During the last years, many investigations were devoted to low energy highly charged ion-fullerene Cgo target collisions. The Cgo is an isolated target that can be considered as an atom-like target in collisions at la...During the last years, many investigations were devoted to low energy highly charged ion-fullerene Cgo target collisions. The Cgo is an isolated target that can be considered as an atom-like target in collisions at large distances. It behaves as a special big 'atom' with 60-7T equivalent loosely bound electrons, which makes possible the formation of hollow atoms via multiply electron capture process W. As the impact parameter is shorter than the radius of the Ceo cage, the Ceo behaves as a tiny solid target. The energy loss of projectiles in such frontal collisions is an important parameter for understanding the energy relaxation in systems wit'h a large number of degrees of freedom.展开更多
In ion-fullerene C60 frontal collisions, an amount of energy is deposited in the C60 target leading to the fragmentation of the C60. Theoretical and experimental investigations have demonstrated that the fragmentation...In ion-fullerene C60 frontal collisions, an amount of energy is deposited in the C60 target leading to the fragmentation of the C60. Theoretical and experimental investigations have demonstrated that the fragmentation scheme of the C60 depends not only on the total excitation energy but also on the nature of the primary electronic and nuclear excitation mechanism. Up to now, the commonly accepted interpretation of the observed mass spectra obtained in ion-C60 experiments is to consider the multi-fragmentation of the C60 being mainly due to the primary electronic interaction. The efficient transfer of the electronic excitation energy towards vibronic modes induces the breakup of the C60 cage in a statistical decay process.展开更多
The interaction between slow highly charged ions and fullerene C60 had been studied extensively during the past few years. In recent experiments performed by Lyon group, they have studied collision systems such as Fq+...The interaction between slow highly charged ions and fullerene C60 had been studied extensively during the past few years. In recent experiments performed by Lyon group, they have studied collision systems such as Fq++C60(q= 1- 3) leading to the production of F-. So the cooperated experiment of Institute of展开更多
Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spec...Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy （LIBS） has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermo-dynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.展开更多
Laser-induced plasma as a spectroscopic emission source was introduced only two years after the invention of the laser. By focusing a pulse delivered by a ruby laser on the surface of a solid target, Brech and Cross i...Laser-induced plasma as a spectroscopic emission source was introduced only two years after the invention of the laser. By focusing a pulse delivered by a ruby laser on the surface of a solid target, Brech and Cross in 1962 first observed optical emission following the laser impact , which later had been further identified as the emission from the plasma produced during the laser ablation process of the impacted target.展开更多
文摘The evolution of a molecular system excited above its ionization threshold depends on a number of parameters that include the nature of the excited states and their couplings to the various continua. The general nature of the processes governing this evolution depends also essentially on the complexity of the molecule, more precisely on its size, density of states, and strength of the couplings among the various internal degrees of freedom. In this paper we address the question of the transition between autoionization that prevails in small molecules, and delayed ionization occurring in larger molecules or clusters. This transition is illustrated by autoionization of Na2 Rydberg states on one hand, delayed ionization in fullerene C60, and delayed detachment in small cluster anions on the other hand. All processes are studied in the case of nanosecond laser excitation, corresponding to a rather slow deposition of the internal energy.
文摘Full quantum mechanical calculations are performed to determine the broadening in the far wings of the cesium D1 and D2 line shapes arising from elastic collisions of Cs atom with inert helium atoms. The potential energy curves of the low-lying CsHe molecular states, as well as the related transition dipole moments, are carefully computed from ab initio methods based on state-averaged complete active space self-consistent field-multireference configuration interaction(SACASSCF-MRCI) calculations, involving the spin-orbit effect, and taking into account the Davidson and BSSE corrections.The absorption and emission reduced coefficients are determined in the temperature and wavelength ranges of 323-3000 K and 800-1000 nm, respectively. Both profiles of the absorption and the emission are dominated by the free-free transitions,and exhibit a satellite peak in the blue wing near the wavelength 825 nm, attributed to B^2Σ1/2^+→ X^2Σ1/2^+/transitions. The results are in good agreement with previous experimental and theoretical works.
文摘During the last years, many investigations were devoted to low energy highly charged ion-fullerene Cgo target collisions. The Cgo is an isolated target that can be considered as an atom-like target in collisions at large distances. It behaves as a special big 'atom' with 60-7T equivalent loosely bound electrons, which makes possible the formation of hollow atoms via multiply electron capture process W. As the impact parameter is shorter than the radius of the Ceo cage, the Ceo behaves as a tiny solid target. The energy loss of projectiles in such frontal collisions is an important parameter for understanding the energy relaxation in systems wit'h a large number of degrees of freedom.
文摘In ion-fullerene C60 frontal collisions, an amount of energy is deposited in the C60 target leading to the fragmentation of the C60. Theoretical and experimental investigations have demonstrated that the fragmentation scheme of the C60 depends not only on the total excitation energy but also on the nature of the primary electronic and nuclear excitation mechanism. Up to now, the commonly accepted interpretation of the observed mass spectra obtained in ion-C60 experiments is to consider the multi-fragmentation of the C60 being mainly due to the primary electronic interaction. The efficient transfer of the electronic excitation energy towards vibronic modes induces the breakup of the C60 cage in a statistical decay process.
文摘The interaction between slow highly charged ions and fullerene C60 had been studied extensively during the past few years. In recent experiments performed by Lyon group, they have studied collision systems such as Fq++C60(q= 1- 3) leading to the production of F-. So the cooperated experiment of Institute of
文摘Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy （LIBS） has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermo-dynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.
文摘Laser-induced plasma as a spectroscopic emission source was introduced only two years after the invention of the laser. By focusing a pulse delivered by a ruby laser on the surface of a solid target, Brech and Cross in 1962 first observed optical emission following the laser impact , which later had been further identified as the emission from the plasma produced during the laser ablation process of the impacted target.
