Infrared spectra of the C2H2-HCl complexes:: An experimental and ab initio study

By means of a pulsed slit jet and an infrared tunable diode laser spectrometer, the vibration-rotation absorption spectra of the complexes C2H2-(HCl)-Cl-35 and C2H2-(HCl)-Cl-37 have been observed for the first time in the 3.6 mu m region of the nu(1) band correlated with the HCl stretch. All the lines of the spectrum have been assigned for J=0 to 18 and K-a=0, 1, 2, 3. To determine the band origin and the rotational and centrifugal constants, the observed line frequencies have been fitted to those determined by the Watson Hamiltonian in the A reduction. A force constant model has been used to derive the binding energy D-e of the complex and the intermolecular stretching harmonic frequency from the experimental spectroscopic constants. The available experimental results concerning these complexes and other isotopic forms (DCl)-Cl-35 and (DCl)-Cl-37 were compared with ab initio calculations performed at the coupled-cluster single double triple [CCSD(T)] level of theory. The comparison turned out to be very good for all the properties considered (geometries, frequencies, energies). (C) 2000 American Institute of Physics. [S0021-9606(00)00436-0].