Photodissociation dynamics through the extended seams of conical intersections for deuterated thioanisole

Abstract

Nonadiabtic transition dynamics through the conical intersection (CI) seam on multidimensional potential energy surfaces inevitably plays an important role in organisms in the aspect of dissipating the harmful excessive UV and re-stabilization of photoexcited biomolecules to prevent the toxic processes. Previously, the related studies were considered as an extension of mathematics and quantum theory because reactive flux stays in a flash at conical intersection. And even more, CIs are widely accepted as they rarely exist on potential energy surfaces. However, as a results of prolonged studies for a few decades, it has been found that conical intersections are ubiquitous and common in polyatomic molecules than previously thought, and moreover, progression of the laser system make it possible to detect the non-adiabatic events experimentally with highly time and energy resolved technique. In this doctorial thesis, nonadiabatic predissociation dynamics occurring in the vicinity of the multidimensional CI seam for partially deuterated thioanisole molecules ($C_6 H_5 S-CH_2 D$ and $C_6 H_5 S-CHD_2$) will be covered intensely. Each isotopomer has two distinct rotational conformers according to the geometrical position of D or H of the methyl moiety with respect to the molecular plane for $C_6 H_5 S-CH_2 D$ or $C_6 H_5 S-CHD_2$, respectively. Nonadiabatic transition probability, estimated by the experimentally measured branching ratio of the nonadiabatically produced ground-state channel giving $C_6 H_5S\cdot (\tilde{X}) versus the adiabatic excited-state channel leading to the $C_6 H_5 S\cdot (\tilde{A})$) radical, shows resonance-like increases at symmetric ($\upsilon$S) or asymmetric (7a) S-CH2D (or S-CHD2) stretching mode excitation in S1 for all conformational isomers of two isotopomers. However, absolute probabilistic value of the nonadiabatic transition is found to vary quite drastically depending on different conformers and isotopomers. High-level potential energy surface calculations along the normal mode coordinates and slow-electron velocity map imaging (SEVI) spectroscopy are quite helpful to understand the correlation between the $\tilde{X}/tilde{A}$ branching ratio and $S_1$ vibronic transition in terms of its conformational structure and vibrational characters. Conformer-specific nonadiabatic transition dynamics for partially deuterated thioanisoles have revealed new dynamic facets of the conical intersection seam using different sets of normal mode coordinates induced by the H/D isotopic substitution, giving another opportunity to unravel multi-dimensional geometrical aspects and spectroscopic characterization of the conical intersection seam.