Computational study on mechanism of hydrogen abstraction and selenium insertion in the reaction of triplet and singlet selenium atom with hydrogen selenide

The reaction pathways of selenium vapor (Se) with hydrogen selenide (H2Se) have been investigated theoretically on the triplet and singlet potential energy surfaces. All species for title reaction have been optimized at the UMP2(FC)/6-311++G(d, p) computational level. The energetic data have been obtained at the UCCSD(T)//UMP2 level employing the cc-pV5Z basis set. Three initial collision complexes, 3IN1 (Se–SeH2), 3IN2 (Se–HSeH) and 1IN1 (Se–SeH2) have been considered for the Se-atom with H2Se reaction on the triplet and singlet potential energy surfaces. Four kinds products HSeSeH, HSe + HSe, H + HSe2 and Se2 + H2 are obtained through variety of transformations of initial reactants and complexes. Calculations reveal that there exist two intersystem crossings between the triplet and singlet potential energy surfaces. Also, the investigation of Se + H2Se reaction paths shows that reaction initiates on the triplet potential energy surface and continues on both triplet and singlet (through intersystem crossing) potential energy surfaces to form the main product of HSeSeH.