TERAHERTZ SPECTROSCOPY OF THE BENDING VIBRATIONS OF ACETYLENE 12C2H2

Twenty P-branch transitions of (C2H2)-C-12 have been measured in the 0.8-1.6 THz region of its bending vibrational difference band. The accuracy of these measurements is estimated to be 100 kHz. The (C2H2)-C-12 molecules were generated under room temperature by passing 150 mTorr H2O vapor through calcium carbide (CaC2) powder. The observed transitions were modeled together with prior far-infrared data involving the bending levels with Sigma(t) V-t (t = 4, 5) <= 2. Frequency predictions of (C2H2)-C-12 in the terahertz region have been greatly improved by adding the first data of "microwave" precision. The new measurements and predictions reported here will facilitate the analyses of astronomical observations by the high spectral resolution telescopes such as Herschel, SOFIA, and ALMA.