New Analysis of the ν3 fundamental band of HDCO: Positions and intensities

Using high-resolution Fourier transform spectra of mono deuterated formaldehyde (HDCO) recorded in the 5.8-μm spectral range at Giessen (Germany), we carried out an extensive analysis of the strong ν3 fundamental band (carbonyl stretching mode) at 1724.2676 cm−1, starting from results of a previous analysis [J.W.C. Johns, A.R.W. McKellar, J. Mol. Spectrosc. 64 (1977) 327-339]. For this hybrid band (with both A- and B-type transitions) the analysis was pursued up to high rotational quantum numbers. In this way, it was possible to evidence a resonance which perturbs the ν3 lines for high Ka values which is due to the existence of the 2ν5 and ν5 + ν6 dark bands in the same spectral region. In addition a local resonance is perturbing the 31 levels in Ka′ = 8 which is due to a crossing with the 41 energy levels in Ka = 11. The model used to calculate the energy levels accounts for the observed A- type, B- type C-type Coriolis (and/or) Fermi resonances which couple the 31 and the 5161, 52, and 41 energy levels. However the 41 state is also involved in strong vibration-rotation interactions coupling the {51,61,41} system of resonation states of HDCO [A. Perrin, J.M. Flaud, L. Margulès, J. Demaison, H. Mäder, S. Wörmke, J. Mol. Spectrosc. 216 (2002) 214-224]. Therefore the final energy levels calculation was performed for the {51,61,41,31,52,5161} resonating states and in this way it was possible to reproduce the observed line positions, within their experimental uncertainties. The present work also led to the determination of the intensity ratio of the B- to A-type components of the ν3 band IA/IB ∼24 band from spectral fittings performed in several parts of the observed spectrum. Finally, using the 5.8 μm band intensity available in the literature we generated, for the first time, a list of line parameters (positions and intensities) for the 5.8 μm region of HDCO.