Isotope Effect in Molecular Rotation of Hydrogen Chloride in Condensed Phase

Abstract

Infrared spectra of HCI and DCI are observed in solid and liquid states to investigate the change in rotational motion of these molecules due to the displacement of the center of mass on isotopie substitution. The moment analysis of measured spectra indicates strongly hindered rotational motion and the mean square torque measured about the center of mass of a DCI molecule is found to be smaller by about 10% than that of a HCI molecule both in β-solid and liquid phases. The difference in mean square torques on isotopie substitution is interpreted as resulting from translation-rotation interaction based on the analysis combined with isotopie vapor pressure data. Discussion is also made on the effective root-mean-square oscillation amplitude associated with molecular rotation from the aspect of corresponding states.

KEYWORDS:

• hydrogen chloride
• deuterium chloride
• infrared spectra
• molecular rotation
• moment analysis
• intermolecular forces
• torque
• rotation-translation interaction
• phase equilibrium
• vapor pressure
• isotope effects
• rotational oscillation
• corresponding states