Nonadiabatic approach for resonant molecular multiphoton absorption processes in intense infrared laser fields

Journal Article · Tue Nov 15 04:00:00 EST 1983 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.445612· OSTI ID:5598389

Ho, T; Chu, S

A nonperturbative approach for efficient and accurate treatment of the molecular multiphoton absorption (MPA) quantum dynamics in intense infrared (IR) laser fields is presented. The approach is based on the adiabatic separation of the fast vibrational motion from the slow rotational motion, incorporating the fact that the IR laser frequency is close to the frequencies of adjacent vibrational transitions. One thus first solves the quasivibrational energy (QVE) states (or, equivalently, the dressed vibrational states) with molecular orientation fixed. This reduces the computationally often formidable (vibrational-rotational) Floquet matrix analysis to a manageable scale, and, in addition, provides useful physical insights for understanding the nonlinear MPA dynamics. The QVE levels are found to be grouped into distinct energy bands, characterized by the IR frequency, with each band providing an effective potential for molecular rotation. Whereas the interband couplings are totally negligible, the intraband nonadiabatic angular couplings are the main driving mechanisms for inducing resonant vibrational--rotational multiphoton transitions. The utility of the method is illustrated by a detailed study of the sequential MPA spectra for /sup 12/C /sup 16/O molecule, including state-to-state multiquantum transitions and transitions from initially thermally distributed states as a whole. Results are presented for the case of IR laser intensity 50 GW/cm/sup 2/ and frequencies ranging from 2115 to 2165 cm/sup -1/. Excellent agreement of the MPA spectra obtained by the nonadiabatic approach and the exact Floquet matrix method was observed in all fine details.

• Research Organization: Department of Chemistry, University of Kansas, Lawrence, Kansas 66045
• OSTI ID: 5598389
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 79:10; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640300* -- Atomic
Molecular & Chemical Physics
74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
ELECTRODYNAMICS
ELECTROMAGNETIC RADIATION
ENERGY LEVELS
EXCITED STATES
FIELD THEORIES
INFRARED RADIATION
INFRARED SPECTRA
LASER RADIATION
MULTI-PHOTON PROCESSES
NONLINEAR PROBLEMS
OXIDES
OXYGEN COMPOUNDS
QUANTUM ELECTRODYNAMICS
QUANTUM FIELD THEORY
RADIATIONS
SPECTRA
VIBRATIONAL STATES