High-intensity multiphoton ionization of H sub 2
- High Temperature Physics Division, Lawrence Livermore National Laboratory, Livermore, California 94550 (US)
A tunable, high-intensity picosecond-dye-laser system has been employed with electron energy analysis to investigate the dynamics of (3+1) resonance-enhanced multiphoton ionization via various vibrational levels of the {ital B} {sup 1}{Sigma}{sub {ital u}}{sup +} and {ital C} {sup 1}{Pi}{sub {ital u}} electronic states in H{sub 2}. At the intensities studied ((0.2--6){times}10{sup 13} W/cm{sup 2}), we find evidence for production of molecular ions in various vibrational levels; at the lower intensities the population distribution of final vibrational states varies with wavelength in a manner consistent with resonant enhancement at the three-photon level, followed by ionization into a vibrational level of H{sub 2}{sup +} roughly predictable by a Franck-Condon analysis of ionization out of the {ital C} state. At higher intensities, there is a shift to increased population of lower vibrational states of H{sub 2}{sup +}, consistent with an ac Stark shift of the correspondingly lower vibrational levels of the {ital C} state into resonance with the three-photon energy of the laser. Clear evidence of direct dissociation of H{sub 2} followed by single-photon ionization of the excited H atom is observed as well. Above-threshold ionization of these two processes occurs readily. We also find that dissociative ionization is an increasingly important ionization pathway as the wavelength is increased. Finally, we see evidence of a fourth ionization pathway, which we tentatively assign to photoionization into a transient bound state created by the avoided crossing of the first repulsive electronic state of H{sub 2}{sup +}, {vert bar}2{ital p}{sigma}{sub {ital u}},{ital n}{r angle}, with the single-photon-dressed ground state of H{sub 2}{sup +}, {vert bar}1{ital s}{sigma}{sub {ital g}},{ital n}+1{r angle}.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5656162
- Journal Information:
- Physical Review, A; (USA), Journal Name: Physical Review, A; (USA) Vol. 44:1; ISSN 1050-2947; ISSN PLRAA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
CHARGED PARTICLES
CORRELATIONS
ELECTROMAGNETIC RADIATION
ELECTRONIC STRUCTURE
ELEMENTS
ENERGY LEVELS
EXCITED STATES
FLUX DENSITY
HYDROGEN
IONIZATION
IONS
LASER RADIATION
MOLECULAR IONS
MULTI-PHOTON PROCESSES
MULTILEVEL ANALYSIS
NONMETALS
PHOTOIONIZATION
RADIATIONS
VIBRATIONAL STATES