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

Reaction pathways for the decomposition of HXCSe (X = H, F, Cl, and Pr) on the singlet state potential energy surface have been studied using the B3LY P/6-311G* level of theory. Predicted molecular parameters (equilibrium geom etries, dipole moments, atomic charges, and rotational constants) and vibra tional IR spectra agree very well with the available experimental data. Fiv e 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 subst itution, the following conclusions emerge: our theoretical findings suggest that selenocarbonyl molecules should be both kinetically and thermodynamic ally stable with respect to the unimolecular decomposition reactions given above. We also report theoretical predictions of molecular parameters and v ibrational IR spectra of some monohalogen substituted selenoformaldehydes, which should be useful for further experimental observations. (C) 2000 Else vier Science B.V. All rights reserved.