Upon light absorption, the 5-atom thioformaldehyde S-oxide sulfine (H<sub>2</sub>CSO) undergoes a rich dynamics resulting in the formation of nine photoproducts. We shed light on the complex photochemical and photodecomposition dynamics by modeling the complete experiment using state of the art techniques. The non-radiative decay to the ground state is described using the <i>ab initio</i> multiple spawning (AIMS) method carried out at the MS-CASPT2 level, while the following dynamics occurring on the ground electronic state is described with Born-Oppenheimer molecular dynamics carried out at the DFT/PBE0 level. We retrieved all the nine photoproducts measured experimentally, including a three membered ring C-S-O oxathiirane and a rare carbon sulfur triple bond acid. Such a large diversity of photoproducts is generally thought to result from different conical intersections connecting excited states to the ground electronic state. However here, only one conical intersection induces an ultrafast decay (&lt;200fs) of the sulfine excited state to its ground state or to the oxathiirane ground state. The myriad of other molecules is then formed on the hot ground state in a sub-picosecond timescale. This dynamics cannot therefore be described by statistical methods such as RRKM because of the highly non-statistical character, as a result of the excited-state dynamics. This unexpectedly rich chemistry occurring on the hot ground state challenges our view of typical photochemical or photodecomposition reactions in which it is the variety of conical intersections that leads to a variety of photoproducts.

Role of the rich athermal ground-state chemistry in the photochemistry of the thioformaldehyde S-oxide sulfine

256th National Meeting (2018)

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