Characterization of the HSiN_HNSi system in its electronic ground state.

The electronic ground states (X (1)Sigma(+)) of HSiN, HNSi, and the transition state connecting the two isomers were systematically studied using configuration interaction with single and double (CISD) excitations, coupled cluster with single and double (CCSD) excitations, CCSD with perturbative triple corrections [CCSD(T)], multireference complete active space self-consistent field (CASSCF), and internally contracted multireference configuration interaction (ICMRCI) methods. The correlation-consistent polarized valence (cc-pVXZ), augmented correlation-consistent polarized valence (aug-cc-pVXZ) (X=T,Q,5), correlation-consistent polarized core-valence (cc-pCVYZ), and augmented correlation-consistent polarized core-valence (aug-cc-pCVYZ) (Y=T,Q) basis sets were used. Via focal point analyses, we confirmed the HNSi isomer as the global minimum on the ground state HSiN_HNSi zero-point vibrational energy corrected surface and is predicted to lie 64.7 kcal mol(-1) (22 640 cm(-1), 2.81 eV) below the HSiN isomer. The barrier height for the forward isomerization reaction (HSiN-->HNSi) is predicted to be 9.7 kcal mol(-1), while the barrier height for the reverse process (HNSi-->HSiN) is determined to be 74.4 kcal mol(-1). The dipole moments of the HSiN and HNSi isomers are predicted to be 4.36 and 0.26 D, respectively. The theoretical vibrational isotopic shifts for the HSiN/DSiN and HNSi/DNSi isotopomers are in strong agreement with the available experimental values. The dissociation energy for HSiN [HSiN(X (1)Sigma(+))-->H((2)S)+SiN(X (2)Sigma(+))] is predicted to be D(0)=59.6 kcal mol(-1), whereas the dissociation energy for HNSi [HNSi(X (1)Sigma(+))-->H((2)S)+NSi(X (2)Sigma(+))] is predicted to be D(0)=125.0 kcal mol(-1) at the CCSD(T)/aug-cc-pCVQZ level of theory. Anharmonic vibrational frequencies computed using second order vibrational perturbation theory are in good agreement with available matrix isolation experimental data for both HSiN and HNSi isomers root mean squared derivation (RMSD=9 cm(-1)).