Orbital angular momentum in triatomic molecules

Abstract

The vibrational and K-type rotational levels of the [Xtilde] 2 B 1 and à 2 A 1 states of NH2 and H2O+ have been fitted by least squares to give sets of Born-Oppenheimer potential curves for the combining electronic states. The model used allows a simultaneous fit to all the observed vibronic levels for each of the two molecules, using a large amplitude formalism and making no approximations other than to neglect Fermi (anharmonic) resonance effects. An accurate description of the effects of orbital angular momentum on the level positions in the two molecules has been obtained, and relative transition moments have been calculated for the vibronic bands of the à 2 A 1-[Xtilde] 2 B 1 transitions. For NH2 the relative transition moments permit the calculation of the emission lifetimes (with the absolute value of the electronic transition moment taken from the ab initio calculations of Peyerimhoff and Buenker); the calculated lifetimes are found to agree very well with the experimental values of Halpern et al., and Donnelly et al. Relative transition moments for the photoelectron spectrum of H2O(H2O+, à 2 A 1 and [Xtilde] 2 B 1 ← H2O, [Xtilde] 1 A 1) have also been calculated. The à 2 A 1 state of H2O+ is confirmed as being linear at equilibrium, with the potential function having an unusual wide flat minimum.