Ab initioMRD-CI study of the Renner-Teller effect and spin-orbit coupling in theX2π ground state of NCO

Abstract

A series of MRD-CI calculations on the bending potential curve of the X 2π ground state of the NCO molecule is reported, whereby the internuclear distances have been kept at their calculated equilibrium values corresponding to r(NC) = 2·36 a.u. (1·25 A) and r(CO) = 2·23 a.u. (1·18 A). The value of the spin-orbit splitting has been calculated to first order in perturbation theory and subsequently employed in a calculation of the vibronic energy levels. The theoretical treatment employs a basis set of 40 bending functions for l 1 = K - 1 and l 2 = K + 1 respectively. Reasonably good quantitative agreement with available experimental data is noted, especially for the low-energy portion of the spectrum. The sign of the spin-orbit splitting for the individual vibronic states exhibits an abrupt change at positions where the levels of the upper Renner-Teller component 1 2 A″ lie above those of the 1 2 A′ state, an effect which is also observed for the NH2 molecule.