Density functional studies on the mechanisms of unimolecular reactions of HXCSe (X=H, F, Cl, and Br)

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Reaction pathways for the decomposition of HXCSe (X=H, F, Cl, and Br) on the singlet state potential energy surface have been studied using the B3LYP/6-311G* level of theory. Predicted molecular parameters (equilibrium geometries, dipole moments, atomic charges, and rotational constants) and vibrational IR spectra agree very well with the available experimental data. Five different reaction mechanisms are proposed: (A) 1,1-HX elimination, (B) 1,2-H shift, (C) 1,2-X shift, (D) H and XCSe radical formation, and (E) X and HCSe radical formation. From a consideration of the effect of halogen substitution, the following conclusions emerge: our theoretical findings suggest that selenocarbonyl molecules should be both kinetically and thermodynamically stable with respect to the unimolecular decomposition reactions given above. We also report theoretical predictions of molecular parameters and vibrational IR spectra of some monohalogen substituted selenoformaldehydes, which should be useful for further experimental observations.