Intramolecular competition in the photodissociation of C3D3 radicals at 248 and 193 nm

Abstract

Motivated by recent experimental work, a theoretical study of the photodissociation of perdeuterated propargyl (D₂CCD) and propynyl (D₃CCC) radicals has been carried out, focusing on the C–C bond cleavage and D₂ loss channels. High-level ab initio calculations were carried out, and RRKM rate constants were calculated for isomerization and dissociation pathways. The resulting reaction barriers, microcanonical rate constants and product branching ratios are consistent with the experimental findings, supporting the overall mechanism of internal conversion followed by statistical dissociation on the ground state surface. We found loose transition states and very low exit barriers for two of the C–C bond cleavage channels and an additional CD₂ + CCD channel, which had not been reported previously. Our results probe the extent of propargyl and propynyl isomerization prior to dissociation at 248 and 193 nm and deliver a comprehensive picture of all ongoing molecular dynamics.