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

Abstract 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 ν 3 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 ν 3 lines for high K a values which is due to the existence of the 2 ν 5 and ν 5  +  ν 6 dark bands in the same spectral region. In addition a local resonance is perturbing the 3 1 levels in K a ′  = 8 which is due to a crossing with the 4 1 energy levels in K a  = 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 3 1 and the 5 1 6 1 , 5 2 , and 4 1 energy levels. However the 4 1 state is also involved in strong vibration–rotation interactions coupling the {5 1 ,6 1 ,4 1 } system of resonation states of HDCO [A. Perrin, J.M. Flaud, L. Margules, J. Demaison, H. Mader, S. Wormke, J. Mol. Spectrosc. 216 (2002) 214–224]. Therefore the final energy levels calculation was performed for the {5 1 ,6 1 ,4 1 ,3 1 ,5 2 ,5 1 6 1 } 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 ν 3 band I A / I B ∼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.