Stretch-Bender Calculations of the Rovibronic Energies in the X̃2B1 Electronic Ground State of NH2

Abstract

The extended stretch-bender Hamiltonian, incorporating spin–orbit coupling and overall rotation, has been used to calculate the spin-vibronic structure of the X̃2B1 state of NH2 up to the barrier to linearity of this state. A detailed comparison has been made with experimental measurements of these rovibronic states, the majority of which are due to Vervloet and his collaborators. We have shown that, in order to fit the variation of the vibronic spin–orbit coupling constant over the whole of this energy regime, the effective linear molecule spin–orbit coupling constant, ASO, must be increased from the earlier value of 50 cm−1 of Ch. Jungen, K.-E. J. Hallin, and A. Merer (Mol. Phys.40, 65–94 (1980)) to 61.6 cm−1. Evidence has also been provided for the large quenching of the spin–orbit coupling as the molecule bends, reflected in the large valuee of gK=6 cm−1. The pattern of calculated spinrovibronic levels, including the effects of spin uncoupling, is in good agreement with that measured experimentally.