Analysis of several high-resolution infrared bands of perdeutero-spiropentane, C5D8

Abstract

Perdeutero-spiropentane (C5D8) has been synthesized and infrared spectra were taken from 400 to 4000 cm−1 at low sample pressures in a 22 m multipass cell. The spectral resolution (0.0015 cm−1) reveals thousands of individual rovibrational transitions for several fundamental bands occurring in the spectral region of 500–1100 cm−1. C5D8 ground state constants reported in a previous study of the ν15 parallel band at 1054 cm−1[1] were improved significantly in the present work by adding combination-differences derived from ν16 parallel and ν24 perpendicular band analyses. The larger data set at higher J values also allowed determination of the ground state K″ = 2 splitting constant (Δ2″ = 0.76(2) × 10−9 cm−1). For ν16, the band origin is 847.16933(5) cm−1 and changes in upper state rotational constants are ΔA = –0.0013411(5) and ΔB = –0.0002021(1) (in units of cm−1). Overlapping, and in Fermi resonance with ν16, is a second parallel band which, from Gaussian calculations at the anharmonic level, is assigned as the b2 combination ν8 + ν12, with band origin of 840.5434(1) and ΔA = –0.0003500(7) and ΔB = –0.0003502(1) cm−1. For ν24 analogous values are 556.41453(2) and ΔA = –0.00032295(9) and ΔB = –0.00016782(4) cm−1. The analyses also yield accurate values for the changes in both quartic and sextic centrifugal distortion constants and, for ν24, values for the l-doubling constants q+ and q−. Theoretical calculations of the rovibrational parameters aided in the analysis and the numerical values are in good agreement with experimental results.