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–H35Cl and C2H2–H37Cl have been observed for the first time in the 3.6 μm region of the ν1 band correlated with the HCl stretch. All the lines of the spectrum have been assigned for J=0 to 18 and Ka=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 De 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 D35Cl and D37Cl 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 con...