MRD-CI calculations for the structure and stability of the hsin-hnsi isomers

Abstract

Ab initio SCF and CI calculations are employed to determine the equilibrium geometrical parameters (bond lengths, stretching force constants and rotational constants B e) for the two isomers HSiN and HNSi. It is found that HNSi is bound relative to H( 2S) + SiN( 2Σ +) by 122 kcal mole −1, whereby the SiN( 2π) state is predicted to lie only 13 kcal mole −1 above SiN( 2Σ +). The HNSi isomer is calculated to be more stable than HSiN by 68 kcal mole −1 (CI treatment) and it is found that only a small barrier exists for angular inter-conversion between the two linear forms. A discussion of these results in the light of similar findings for other HAB systems containing first- and second-row atoms is presented Finally it is concluded on the basis of the present calculations that neither HNSi nor HSiN is a likely source for the observed interstellar molecular line U 81.5 ( J = 2 → 1).