Photodissociation Dynamics and Stereodynamics of Methyl Mercaptan and Dimethyl Sulfide from the Second Absorption Band at 201 and 210 nm

Abstract

The role of promoting and spectator modes vs. energy randomization in nonadiabatic dynamics is interrogated in the photodissociation of methyl mercaptan, CH 3 SH, and dimethyl sulde, CH 3 SCH 3 or DMS, in the second absorption band. The primary 1 CH 3 (ν) radicals produced in the dissociation of both systems at 210 nm have been resonantly detected in slice-imaging experiments and the corresponding translational energy and angular distributions have been obtained. The stereodynamical information provided by Dixon's bipolar moments in conjunction with the energy partitioning among the dierent degrees of freedom of the primary CH 3 (ν) products oers a panoramic picture of the photodissociation process of both systems. The remarkable similitude found between the two systems related to both vector correlations and internal energy content of the corresponding counterparts − SH for methyl mercaptan and SCH 3 for DMS − indicates that despite the diabaticity of the process, no ecient energy randomization of the available energy takes place. More specically, only the parent vibrational modes whose participation in the initial absorption step is imposed by the conical intersection − i.e. the promoting modes − are adiabatically preserved during the process, while the rest of the vibrational modes play the spectator role. The results for both molecules at 210 nm are complemented with experiments carried out for DMS at 201 nm to explore the internal mechanism of the conical intersection in dierent zones of the absorption region.

Photochemical carbon–sulfur bond cleavage in thioethers mediated via excited state Rydberg-to-valence evolution

“…Our interpretation/assignment of the higher probe intensity spectral feature in DES is also consistent with photofragment REMPI studies conducted on the related dimethylsuflide molecule following excitation at 201 nm. 66 Here a bimodal CH 3 translational energy distribution was observed, with both components exhibiting strong recoil anisotropy (indicating dissociation on a timescale faster than the period of molecular rotation). The higher kinetic energy feature was attributed to S–C bond cleavage within the parent molecule, while the lower kinetic energy feature was thought to be prompt secondary dissociation of the resulting SCH 3 co-fragment.…”