AbstractThe infrared spectra of mixtures of HC1 and the following have been recorded in the gas phase and low temperature matrices: argon, ethene, ethyne, de-benzene, fluorobenzene, CO, CO 2 , SOz, CC1*, CHCls, de-acetone, ethanal, HCN and acrylonitrile. The features which have been measured are: firstly the changes in the integrated intensity of lines in the rotation-vibration spectrum of the fundamental HC1 band as a function of interactions with other components of the mixture, and secondly bands associated with specific interactions forming hydrogen-bonded complexes.
The enhancement of HC1 is generally found to vary linearly with the pressure of added gas over a limited pressure range. Assuming that line enhancement is caused by collisionally-induced rotation-translation energy exchange to or from the HC1 molecule, a combination of expressions derived from Ehrenfest's Adiabatic Principle and the "rigid rotor" approximation leads to a model which qualitatively predicts the enhancements observed. The model also rationalises the enhancement of HCN and SOa absorptions by HC1.
Examination of the experimentally determined data leads to the conclusion that the total intermolecular force between the monomer base and HC1 controls the degree of enhancement but it is concluded that there is no general connection between the degree of HC1 enhancement and hydrogen-bond strength.
Hydrogen-bonded complexes were examined in the gas and argon matrix phases and the shifts in the modified hydrogen chloride stretch compared for various bases. The spectra of pi-complexes formed between HC1 and ethene, ethyne and benzene were found to be detectable by low-resolution infrared spectroscopy at room temperature. Complexation of HCN, he-acetone and de-acetone with HC1 caused CN and C=O band shifts.
The Chem-X molecular modelling program was evaluated by using it to predict the geometry of simple complexes for which experimental data is already available. It is concluded that the program requires more development before it can be confidently used as a theoretical aid with which to study hydrogen-bonded dimers.
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