Argon hydrochloride, Ar⋅HCl, bond energy by infrared spectroscopy

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Abstract
The infrared absorption of argon (200–760 torr) and hydrogen chloride (2–6 torr) mixtures has been re‐examined in the spectral region 2860–3010 cm−1 (the missing Q branch region) over the temperature range 195–298°K. The temperature dependence of two absorption features of the Ar⋅HCl complex, at 2887 and 2879 cm−1, lead to a bond energy estimate that depends upon the assumptions made about the internal degrees of freedom of the complex. Agreement with experiment can be reached for well depths near 1.2 kcal/mole, a result that is relatively insensitive to the choices of the vibrational frequencies and anharmonicities but which does depend upon the extent to which the energy level manifolds are truncated to avoid molecular excitation in excess of the bond energy. This bond energy contrasts with the commonly accepted value of 0.4 kcal/mole; the possible origin of the disparity is considered.