Fine Structure and Λ Splitting – Resolved Rotational Energy Transfer of SH (X2Π, v〃=0 and A2Σ+, v′=0) by Collisions with Ar
Date Issued
2010
Date
2010
Author(s)
Tsai, Po-Yu
Abstract
Rotational energy transfer (RET) among the SH (A2Σ+, v′=0) and (X2Π, v〃=0) ro-vibrational levels by collisions with Ar has been studied in both theoretical and experimental manners. The SH (A2Σ+) state is probed using a laser-induced dispersed fluorescence technique, following photodissociation of H2S at 248 nm. The Ar pressure is adjusted appropriately to allow for significant observation of RET process in single collision condition. The spin-resolved rate constants are then evaluated with the aid of a kinetic model: Firstly, a set of rate constants is determined from experimental data by assuming single collision approximation. Then such initial guess values are substituted into rate equation and an iterative process is performed in order to obtain converged rate constants which incorporated the multi collision effect. The theoretical counterparts of both SH (A2Σ+ v′=0) and (X2Π v〃=0) can be calculated by using quantum scattering method with newly fitted potential energy functions based on ab initio potential energy surfaces. Although the Λ doublet resolved rate constants of SH (X2Π, v〃=0) are merely determined via theoretical calculation, experimental time resolved rotational populations are measured via laser induced fluorescence (LIF) technique and compared with simulation in order to examine the reliability of theoretical data. For the SH (A2Σ+ v=0) case, the experimental and theoretical kinetic results are essentially consistent in the trend of N (spinless angular momentum quantum number) and ΔN dependence. The principle of microscopic reversibility is also examined for both experimental and theoretical kinetic data, showing that translational energies of the RET collisions are close to thermal equilibrium at room temperature. Fine structure conserving propensity is found in the fine structure resolved rate constants. Such propensity can be rationalized according to angular momentum vector model. For the SH (X2Π, v〃=0) results, RET rate constants of Λ doublet levels are determined theoretically. In order to examine the reliability of theoretical data, experimental time resolved SH (X2Π, v〃=0) rotational populations are measured via LIF technique and compared with theoretical simulation. Several propensity rules are found in the Λ resolved rate constants, either favor the final level with certain reflection symmetry or tend to conserve the parity. Explanations are given for these propensity rules, basing on both the high collision energy limit and the interference effect in interaction potentials.
Subjects
rotational energy transfer
SH radical
inelastic collision
laser induced fluorescence
quantum scattering calculation
Type
thesis
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