High-resolution infrared studies of perdeutero-spiropentane, C5D8

Abstract

Perdeutero-spiropentane (C5D8) has been synthesized, and infrared and Raman spectra are reported for the first time. Wavenumber assignments are made for most of the fundamental vibrational states. Gas phase infrared spectra were recorded at a resolution (0.002cm−1) sufficient to resolve individual rovibrational lines and show evidence of strong Coriolis and/or Fermi resonance interactions for most bands. However a detailed rovibrational analysis of the fundamental ν15 (b2) parallel band proved possible, and a fit of more than 1600 lines yielded a band origin of 1053.84465(10)cm−1 and ground state constants (in units of cm−1): B0=0.1120700(9), DJ=1.51(3)×10−8, DJK=3.42(15)×10−8. We note that the B0 value is significantly less than a value of Ba=0.1140cm−1 calculated using structural parameters from an earlier electron diffraction (ED) study, whereas one expects Ba to be lower than B0 because of thermal averaging over higher vibrational levels. A similar discrepancy was noted in an earlier study of C5H8 (Price et al., 2011). The structural and spectroscopic results are in good accord with values computed at the anharmonic level using the B3LYP density functional method with a cc-pVTZ basis set.