Torsional Splitting in the Degenerate Vibrational States of 70Ge2H6: Rotation–Torsion Analysis of the ν7 and ν9 Fundamentals

Abstract

The rotational and torsional structure of the ν7 and ν9 degenerate fundamentals of 70Ge2H6 has been analyzed under high resolution. The torsional structure of both v7 = 1 and v9 = 1 states can be fitted by a simple one-parameter formula. The x,y-Coriolis interaction with the parallel ν5 fundamental was accounted for in the analysis of ν7. A strong perturbation of the J structure of the E3s torsional component of the KΔK = −2 subbranches of ν9 can be explained by the resonance with an E3s excited level of the pure torsional manifold. The perturber is centered at 361.58 cm−1, very close to the value estimated with a barrier height of 285 cm−1. This confirms that the fundamental torsional wavenumber is close to 103 cm−1, in good agreement with the “ab initio” prediction. The torsional splittings of all the infrared active degenerate fundamentals, ν7, ν8, and ν9, follow the trend predicted by theory, and have been fitted by exploratory calculations accounting only for the torsional Coriolis-coupling mechanism of all degenerate vibrational fundamentals in several torsional states. This confirms that torsional Coriolis coupling is the dominant mechanism responsible for the decrease of the torsional splitting in the degenerate vibrational states. A higher value of the barrier had to be used for the ν9 mode.