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Nonadiabatic approach for resonant molecular multiphoton absorption processes in intense infrared laser fields
Ho, Tak-San ; Chu, Shih-I
Ho, Tak-San
Chu, Shih-I
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Abstract
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 (vibrationalārotational) 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 vibrationalārotational multiphoton transitions. The utility of the method is illustrated by a detailed study of the sequential MPA spectra for 12Cā16O molecule, including stateātoāstate multiquantum transitions and transitions from initially thermally distributed states as a whole. Results are presented for the case of IR laser intensity 50 GW/cm2 and frequencies ranging from 2115 to 2165 cmā 1. Excellent agreement of the MPA spectra obtained by the nonadiabatic approach and the exact Floquet matrix method was observed in all fine details.
Description
This is the published version, also available here: http://dx.doi.org/10.1063/1.445612.
Date
1983-07-14
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Elsevier
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Keywords
Non adiabatic reactions, Molecular dynamics, Infrared lasers, Multiphoton absorption, Infrared spectra
Citation
Chu, Shih-I. & Ho, Tak-San. "Nonadiabatic approach for resonant molecular multiphoton absorption processes in
intense infrared laser fields." The Journal of Chemical Physics 79, 4708 (1983); http://dx.doi.org/10.1063/1.445612.