15min:

HOLGER S. P. MÜLLER, CHRISTIAN P. ENDRES, STEPHAN SCHLEMMER, I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany; ATSUKO MAEDA, IVAN MEDVEDEV, ERIC HERBST, MANFRED WINNEWISSER, FRANK C. DE LUCIA, Department of Physics, The Ohio State University, Columbus, OH 43210, USA.

Rotational spectra of vibrationally excited states of H₂CS below 1500~cm^-1 have been obtained by long-path absorption spectroscopy between 120 and currently 670~GHz. The highest K_a accessed range from 9 to 12 and correspond to combined rotational and vibrational energies of almost 2400~cm^-1. The v₄ = 1 (990.185~cm^-1) and v₆ = 1 (991.019~cm^-1) states are almost degenerate and undergo very strong Coriolis interaction (| ₄₆^a| = 0.5148) which causes K_a > 0 to be mixed completely. The v₃ = 1 state is at 1059.204~cm^-1 and the first order Coriolis terms are smaller (| ₃₆^c| = 0.2743 and | ₃₄^b| = 0.0574) so that perturbations are more local. Finally, the v₂ = 1 state (1455.496~cm^-1) is comparatively far away from the three lower states, but there is a large coupling term with v₄ = 1: | ₂₄^b| = 0.8555. Because of the large energy difference, only higher order effects are pronounced in this case. The initial assignments were greatly facilitated by previous infrared studies on ₄, ₆, and ₃ as well as on ₂. The results from these as well as previous and present pure rotational studies on the ground vibrational state were considered in the global fit. The very satifactory fit required a modest number of vibrational corrections for the four vibrationally excited states and a comparatively large number of Coriolis interaction terms.