Gas-Phase Complexes in Hydrogen Chloride

Abstract

The null gap region of the fundamental band of HCl has been studied in the case where argon and xenon are used as perturbing gases. The experiments were performed using an absorption cell of 150 cm length. The absorption cell could be varied in temperature from room temperature to 195°K. The complex features previously observed in the spectrum at room temperature were greatly enhanced in intensity at the lowest temperature. The absorption spectrum of pure HCl gas was found to show strong evidence for dimer formation, which feature becomes strikingly evident at the lowest temperature employed. ``Arrhenius'' plots were made of the HCl–Ar, HCl–Xe, and the dimer data. The heats of formation were found to be 1.1, 1.6, and 2.14 kcal/mole, respectively, with a probable error of ±0.2 kcal/mole. The concentration of the dimer is estimated to be 1 part in 50 000 at 195°K at a gas density of 0.36 amagat.