Rotation-Torsion Analysis of the High-Resolution nu(6) and nu(8) Fundamentals of (70)Ge(2)H(6)

The nu(6) (A(4s)) and nu(8) (E(1d)) Coriolis coupled fundamental bands of (70)Ge(2)H(6), occurring between 730 and 950 cm(-1), have been rotationally analyzed under high resolution. The interactions of nu(8) with the nearby lying nu(2) + nu(4) (A(4s)), 2nu(3) + nu(9) (E(1d)), and nu(-/+1)(9) + nu(-/+1)(12) (E) have also been accounted for in the analysis. We determined rotational constants of the ground state, vibrational and rotational parameters of nu(6) and nu(8), interaction parameters, and a few leading parameters of the other three mentioned perturbers of nu(8). The torsional barrier height is estimated about 285 cm(-1), leading to the prediction of a tunneling splitting of about 0.049 cm(-1) in the ground torsional state. No torsional splitting was observed in the nu(6) band, showing that the splittings in the v(6) = 1 vibrational state are the same as in the ground state. The nu(8) band shows almost constant splittings of about 0.047 cm(-1). This result and the assignments of the split torsional components in all the observed subbranches of nu(8) show that the torsional splittings in the v(8) = 1 state are quite small, and the observed splittings are almost completely due to the ground state. We have proved by numerical calculation that the lowering of the torsional splitting found in the v(8) = 1 state can be explained by the vibration-torsion (gamma-Coriolis) coupling mechanism of the degenerate vibrational states. Copyright 1999 Academic Press.