Effect of rotational relaxation on isotopic selectivity of IR multiphoton dissociation

Quantum stochastic modeling energy transfer and effect of rotational and V‐T relaxation on multiphoton excitation and dissociation for CF3Br molecules

“…To get a quantitative agreement between theory and experiment, we start from the kinetic equations, describing the temporal behavior of occupancy of the vibrational levels of the molecule in a laser field. Usually the vibrational spectrum is qualitatively divided into the parts of the low‐lying discrete states and high‐excited levels of the quasicontinuum 1, 6. At some definite energy threshold the vibrational energy can be randomly distributed among the vibrational modes during the interaction with the laser pulse.…”

“…The excitation process into a continuum can be described by the following system of the generalized kinetic equations 2–4, 6, 8: where z n are the populations of the laser‐excited states with energy E n ; W n,n ±1 is the rate of the radiative transitions; W n,n ±1 = σ n,n ±1 I ( t ), where σ n,n ±1 are the cross‐sections of the radiative transitions up and down, I ( t ) is the laser radiation intensity (photon · cm −2 · s −1 ); k VT n,n ±1 are the constants of rate of the V‐T relaxation; d n is the monomolecular decay rate; Θ( n‐N min ) is the Heaviside function as an additional multiplier in the diffusion coefficient D ( R ) n 3 , which “freezes” the stochastic processes in the area of the low‐lying states according to the well‐known Chirikov's criterion 10. The key difference between our model and other theoretical models is in an explicit accounting for effect of the stochastic diffusion in the quasicontinuum.…”

“…According to Refs. 2–4, 6 the collisional redistribution of populations is determined by the probability function of transition due to the collision k ( E → E ′). The physically significant variable is an energy, transmitted during collision: The similar parameter in Eq.…”

“…All these processes are characterized by the highly nonlinear interaction between the molecule and external laser field. While the dynamic aspects of ionization of molecules in a strong laser field are considered to be well understood, at least within quantitative simplified models, the multiphoton dissociation and excitation is a topic of active interest 1–9. A majority of the experiments of studying the multiphoton excitation and dissociation processes in molecules has been fulfilled under the conditions when the collisional factor may be missed.…”

“…The quantitative comparison of experiments on the multiphoton dissociation with theoretical results, including radiative and collisional processes, has been discussed in many articles 2–7. A phenomenological approach to describe the noncollisional excitement for a number of molecules ( CF 3 I, SF 6 , OsO 4 ) has been realized by Letokhov and colleagues 5, 6. At the same time, the problem of a correct account for the influence of collisions on dynamics of the multiphoton processes, absorption, and energy transfer, etc., requires further study.…”