Signs of l-doubling constants in NF3

Computed infrared band contours are presented for the two degenerate fundamentals of the NF3 molecule, using the l-resonance band contour program described by Cartwright and Mills, with values of the vibration-rotation constants determined from the microwave spectrum by Morino and co-workers. Computed contours are presented for both possible signs of the l-doubling constant, and comparison with the observed band contours leads to the conclusion that q3 = −121.4 MHz and q4 = +51.4 MHz.

Potential energy surface intersections in triatomic molecules

The different types of surface intersection which may occur in linear configurations of triatomic molecules are reviewed, particularly with regard to the way in which the degeneracy is split as the molecule bends. The Renner-Teller effect in states of symmetry Π, Δ, Φ, etc., and intersections between Σ and Π, Σ and Δ, and Π and Δ states are discussed. A general method of modelling such intersecting potential surfaces is proposed, as a development of the model previously used by Murrell and Carter and co-workers for single-valued surfaces. Some of the lower energy surfaces of H2O, NH2, O3, C3, and HNO are discussed as examples.