Evolution of IR spectra of a weakly-bound OCO⋯HCl complex with increasing CO2 density from the gas to liquid phase

Abstract

The IR spectra of HCl/CO2 mixtures have been measured at CO2 densities increasing from the gas to liquid phase at T∼290–230K. The spectroscopic data show a weakly bound OCO⋯HCl complex formation in the mixtures. The fundamental νc(HCl) and first overtone 2νc(HCl) bands of the complex and the combination bands, originated from simultaneous excitation of the HCl and CO2 subunits were studied. The spectral characteristics (frequencies, widths and intensities) of all the bands of the complex have been determined. Ab initio calculations utilizing the 6-311++G(3df,3pd) basis set with electron correlation at the MP2 level of approximation predict a potential energy minimum of ∼6.3kJmol−1 for the H-bonded OCO⋯HCl linear structure and give reasonable values of red shift for the HCl fundamental frequency and of blue shift for the CO2 fundamental asymmetric stretch frequency relative to free HCl and CO2 molecules, respectively. The results obtained suggest anharmonic coupling between the stretching νc(HCl) and high frequency bending νB(ClH⋯OCO) modes of the complex.