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 (0.002 cm⁻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 v₁₅ (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) x 10⁻⁸, Dⱼₖ = 3.42(15) x 10⁻⁸. We note that the B₀ value is significantly less than a value of Bₐ = 0.1140 cm⁻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