Torsional splitting in the degenerate vibrational states of (Ge2H6)-Ge-70:Rotation-torsion analysis of the nu(7) and nu(9) fundamentals

The rotational and torsional structure of the v(7) and v(9) degenerate fund amentals of (Ge2H0)-Ge-70, has been analyzed under high resolution. The tor sional structure of both v(7) = 1 and v(9) = 1 states can be fitted by a si mple one-parameter formula. The x,y-Coriolis interaction with the parallel v(5) fundamental was accounted for in the analysis of v(7). A strong pertur bation of the J structure of the E-3s torsional component of the K Delta K = -2 subbranches of v(9) can be explained by the resonance with an E-3s exc ited level of the purl 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 torsion al splittings of all the infrared active degenerate fundamentals, v(7), v(8 ), and v(9), follow the trend predicted by theory, and have been fitted by exploratory calculations accounting only for the torsional Coriolis-couplin g mechanism of all degenerate vibrational fundamentals in several torsional states. This confirms that torsional Coriolis coupling is the dominant mec hanism responsible for the decrease of the torsional splitting in the degen erate vibrational states. A higher value of the barrier had to be used for the v(9) mode. (C) 2000 Academic Press.