Frequency analysis of the nu(9) band of ethane-d6: Experiment and ab initio calculations.

摘要

The infrared gaseous spectrum of CD3CD3 has been measured in the range of 530--670 cm-1 to investigate vibration-torsion effects in the nu9 band. Three separate spectra all taken under different experimental conditions were recorded. The lines with (DeltaK = -1) and with high values of K show torsional splittings that are substantially larger than expected from the observed barrier height. These splittings are caused primarily by Coriolis-type interactions between the torsional stack of v 9 = 1 and the corresponding stack for the ground vibrational state. Because of a near-degeneracy that exists between the states (v 9 = 0, v4 = 3) and (v 9 = 1, v4 = 0), three subbands ( K,sigma) = (15,1), (16,2), (17,3) are resonantly perturbed. For these cases, perturbation-allowed 3nu4 torsional transitions have been identified. Here sigma = 0, 1, 2, or 3 labels the torsional sublevels. Measurements from the nu9 and 3nu4 bands, frequencies from the far-infrared torsional spectra in the ground vibrational state, and lower state combination differences from nu9 + nu4 - nu 4 band were fitted to within experimental uncertainty using an effective Hamiltonian which considered three torsional stacks: one for the ground vibrational state and two for v9 = 1. In all, 22 parameters were determined using a total of 2001 lines. Of these, 3 parameters were the interstack couplings, 8 are from the ground vibrational state and 11 are from the excited vibrational state.