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A discrepancy between theoretical and experimental values of the rotational barrier in benzaldehyde has been observed, which was attributed to inaccurate experimental results in part. Here, we report results on the -CHO torsion of benzaldehyde (C6H5CHO) based on a high resolution spectroscopic investigation in the far-infrared range in an effort to remove the experimental ambiguity. The rotationally-resolved vibrational spectra were measured with an unapodized resolution of 0.00064 cm-1 using synchrotron-based Fourier transform infrared (FTIR) spectroscopy at the Canadian Light Source. The torsional fundamental νt = 109.415429(20) cm-1 was unambiguously assigned via rovibrational analysis, followed by the tentative assignment of the first (2νt-νt) and second (3νt- 2νt) hot bands at 107.58 cm-1 and 105.61 cm-1, respectively, by comparison of the observed Q branch structures at high resolution with simulation based on a previous microwave study. This assignment is different from any previous low resolution infrared studies in which the intensity patterns were misleading. The key result of the assignment of the first three transitions allowed the determination of the barrier to internal rotation of (hc)1533.6 cm-1 (4.38 kcal mol-1). When compared with calculated results from vibrational second-order perturbation theory (VPT2) and the quasiadiabatic channel reaction path Hamiltonian (RPH) approach, the experimental value is still too low and this suggests that the discrepancy between theory and experiment remains despite the best experimental efforts.

Propene infrared absorption cross-sections are important for quantitative analysis of atmospheric spectra. Propene has been observed in Titan's atmosphere and may be detected in the atmospheres of giant planets. Infrared absorption cross-sections of propene (C3H6) have been measured in the 2680–3220 cm−1 region by high-resolution Fourier transform spectroscopy. Samples of propene were held at 202, 232, 265, 295 K with helium and nitrogen broadening gas pressures of 10, 30, 100 Torr. The cross section files are available for download.

The rotational spectrum of thiazole (c-C3H3NS, Cs, μa = 1.3 D, μb = 0.97 D) from 130 to 375 GHz and high-resolution infrared spectrum from 300 to 1300 cm−1 were obtained and analyzed. Nearly 4700 new, pure-rotational transitions were measured for the ground vibrational state, as well as over 1400 transitions for each of its three lowest-energy vibrationally excited states (ν18, ν17, and ν13). A total of over 5500 rotationally resolved, infrared transitions were measured for fundamentals ν17 and ν13, which form a Coriolis-coupled dyad. Transitions for each of these vibrational states of thiazole were fit to a sextic, A-reduced Hamiltonian in the Ir representation. Computed CCSD(T) values of the spectroscopic constants of thiazole show remarkable agreement with the experimentally determined values. Deuterium enrichment of thiazole allowed for the observation of the ground state and first fundamental (ν18) for three isotopic thiazoles. The direct impact on ν18 by isotopic substitution at C2 and C5 is observed. The combined rotational and high-resolution IR data allowed for an excellent fit of the Coriolis-coupled dyad of ν17 and ν13, which includes more than 60 nominal interstate transitions. Some of the measured resonant transitions are displaced by more than 30 GHz. The least-squares fit yielded six Coriolis coupling terms ( G a , G a J , G a K , G b , G b J , and G b K ) and very accurate measurements of the ν17 and ν13 band origins, 603.8511589 (17) cm−1 and 611.2214645 (18) cm−1, respectively. Collectively, these data provide reliable spectroscopic constants that can be used to predict the rotational spectra of thiazole up to 360 GHz.

The infrared absorption cross sections of ethane (C2H6) have been measured in the 3.3 µm region by high resolution Fourier transform spectroscopy. The ethane samples had temperatures of 203, 233, 263, 295 K with broadening gas pressures of 10 Torr, 30 Torr and 100 Torr of hydrogen or helium. These cross sections are useful for the interpretation of spectra of the giant planets.

Infrared absorption spectra of neopentane, 2,2-dimethylpropane, C(CH3)4, were recorded in the 2550-3350 cm-1 region by high resolution Fourier transform spectroscopy at the Canadian Light Source (CLS). Absorption cross sections were obtained for pure samples and with nitrogen as a broadening gas for 4 temperatures (202, 232, 265, 297 K).

Near infrared absorption spectra of ethane (C2H6) were recorded in the 1800–6200 cm−1 region by high resolution Fourier transform spectroscopy (Bruker IFS 125 HR) at the Canadian Light Source (CLS). Absorption cross sections were obtained for pure samples and with nitrogen or hydrogen as broadening gases as appropriate for astronomical environments. Corrections to the cross sections were made using data from the Pacific Northwest National Laboratory (PNNL) infrared database.