Observation and Rovibrational Analysis of the Intermolecular HCl Libration Band in OC−HCl. Modeling of the Intermolecular Potential Energy Surface

The high-resolution far-infrared spectrum of the intermolecular HCl libration band of the OC−H 35 Cl heterodimer is recorded in the gas phase by means of Fourier transform IR spectroscopy in a static multipass absorption cell at 137 K using a synchrotron radiation source. This is the first direct observation of an intermolecular vibration band of the OC−HCl dimer in the gas phase. The rotational structure of the band has the typical appearance of a perpendicular band of a linear polyatomic molecule. The structure is analyzed to yield the band origin ν 0 = 201.20464(27) cm -1 together with values for the upper state rotational constant, the upper state quartic and sextic centrifugal distortion constants, and the l -type doubling constant. The determined values for the rotational constant and the centrifugal distortion constants are used to obtain a Morse potential for the stretching of the intermolecular distance. The results are compared to the results from quantum-chemical calculations.