Absolute intensities of the fundamental vibrational bands of HCl and HBr have been measured in the absorption spectrum of crystalline films. The path length has been determined from the interference fringes of the transmitted light as the film is deposited on a window, following the technique of Hollenberg and Dows. The measured integrated molar absorption coefficientsBare 24 000plusmn;3000 and 17 600plusmn;1200 darks (cmmdash;1cm2/mM), respectively, for HCl and HBr. These values are larger than the gas phase intensities by factors of 6 and 13, respectively. Such large intensification of an Xmdash;H stretching vibration is consistent with the large frequency shift and is characteristic of hydrogenhyphen;bonded crystals. The results are compared with those from other hydrogenhyphen;bonded systems. Furthermore, the high intensities are consistent with those required by Hornig and Hiebert using the transition dipolemdash;transition dipole model to explain the observed intermolecular force constants. However, it is likely that other terms contribute as much to these constants. Finally, the formalism used by Hexter to express the frequencies in molecular crystals is modified slightly so that hydrogenhyphen;bonded crystals can be treated.
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