High resolution overtone spectroscopy of the acetylene van der Waals dimer, (12C2H2)2

• Published in: Physical chemistry chemical physics : PCCP 2011-01, Vol.13 (31), p.14010-14018
• Main Authors: Didriche, K., Lauzin, C., Földes, T., Golebiowski, D., Herman, M., Leforestier, C.
• Format: Article
• Language: English
• Subjects: Atomic and Molecular Clusters; Constants; Dimers; Excitation; Fittings; Physics; Spectroscopy; Stacks; Symmetry; Tunneling
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c1cp20561g

CW-cavity ring down spectroscopy was used to record in a free jet expansion the spectrum of the absorption band in (12C2H2)2 with origin at 6547.6 cm-1. It is a perpendicular band and corresponds to 2CH excitation in the hat unit of the T-shaped dimer. Calibration (better than +/-1 [times] 10-3 cm-1 accuracy) and ring-down time (130 [small mu ]s) were improved compared to a previous contribution (Didriche et al. Mol. Phys., 2010, 108, 2158-2164). A line-by-line analysis was achieved. Three series of lines were identified involving levels with A1+, E+ and B1+ ground state tunneling symmetries, confirming the spectral and symmetry analyses reported in the literature for the 1CH excitation band (Fraser et al. J. Chem. Phys., 1988, 89, 6028-6045). 164 vibration-rotation-tunneling lines were assigned in the sub-bands and effective rigid rotor vibration-rotation constants were obtained by simultaneously fitting 1CH and 2CH lines with the same symmetry series. Perturbations affecting the Ka stacks, in particular, are reported. The tunneling frequency in 2CH is estimated to be [small nu]2CHtunn = 270 MHz for the Ka = 0 stack. The rotational temperature is determined to be 23 K from relative line intensities and the lifetime of the dimer in the 2CH hat state is estimated to be 1 ns from individual line widths.