The bending frequency δNS of dinitrogen sulfide (N2S): A theoretical analysis demonstrating the importance of Coriolis coupling terms

Abstract

There exists a discrepancy between theory and experiment for the N2S bending vibrational frequency. Ab initio molecular electronic structure theory has been used in order to investigate the electronic ground state of the dinitrogen sulfide (N2S) molecule. Self-consistent field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD) wave functions were employed using the three basis sets, the double zeta plus polarization (DZP), triple zeta plus double polarization (TZ2P), and TZ2P with one set of higher angular momentum polarization functions (TZ2Pf). For CCSD wave functions the connected triple excitations were included through perturbation theory [CCSD(T)]. Using the CCSD(T) method with the larger basis sets, experimental physical properties including bond lengths, rotational constant, centrifugal distortion constant, l-type doubling constant, vibrational frequencies, and isotopic shifts for the N–N stretching frequency have been reproduced with quantitative accuracy. This analysis proves the essential correctness of an earlier theoretical prediction of the N2S harmonic bending vibrational frequency.