Spin-Forbidden Channels in Reactions of Unsaturated Hydrocarbons with O(3P)

22 October 2018, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Electronic structure of four prototypical Cvetanovic diradicals, species derived by addition of O(3P) to unsaturated compounds, is investigated by high-level electronic structure calculations and kinetics modeling. The main focus of this study is on the electronic factors controlling the rate of inter-system crossing (ISC), minimal energy crossing points (MECPs) and spin-orbit couplings (SOCs). The calculations illuminate significant differences in the electronic structure of ethylene- and acetylene-derived compounds and a relatively minor effect due to methylation. The computed MECPs heights and SOCs reveal different mechanisms of ISC in ethylene- and acetylene-derived species, thus explaining variations in the observed branching ratios between singlet and triplet products and a puzzling effect of the methyl substitution. In the ethylene- and propylene-derived species, the MECP is very low and the rate is controlled by the SOC variations, whereas in the acetylene- and propyne-derived species the MECP is high and the changes in the ISC rate due to methyl substitutions are driven by the variations in MECP heights.


spin-forbidden process
spin-orbit coupling
atmospheric chemistry
density analysis
natural transition orbitals
unsaturated hydrocarbons
intersystem crossings
Cvetanovic diradicals
minimal energy crossing point
non-adiabatic transition
non-adiabatic transition state theory
El-Sayed rule

Supplementary materials



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