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

• Published in: Journal of molecular spectroscopy Vol. 372; p. 111350
• Main Authors: Nibler, J.W., Erickson, B.A., Brauer, C.S., Masiello, T., Blake, T.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.07.2020
• Subjects: Anharmonic frequencies; C5H8 and C5D8; High-resolution infrared spectrum; L-doubling; Molecular structure: DFT study; Rovibrational constants; Spiropentane; L-doubling; C5H8 and C5D8; Rovibrational constants; High-resolution infrared spectrum; Anharmonic frequencies; Spiropentane; Molecular structure: DFT study
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/j.jms.2020.111350

[Display omitted] •High-resolution infrared absorption spectra are reported for perdeutero-spiropentane, C5D8.•Detailed rovibrational analyses are presented for three bands of this D2d symmetric top molecule.•From level-splittings, two l-doubling constants, q+ and q−, were determined for the ν24 fundamental.•The results are compared with those obtained from density functional calculations at the anharmonic level. 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.