A rigid rod normal coordinate analysis, and van der Waals force field of acetylene–HCl

Abstract

A normal coordinate analysis appropriate for two weakly bound rigid rods is developed. Asymmetric top centrifugal distortion constants and published vibrational frequencies are employed in the normal coordinate analysis to obtain the intermolecular force field and refinements in the structural parameters. The analysis permits a more accurate interpretation of the observed Cl quadrupole coupling constant suggesting that the hydrogen bonding in this complex causes a decrease in the magnitude of the electric field gradient at Cl by 8±1% from that in the free HCl monomer. These methods also suggest that hydrogen bonding decreases the electric field gradient at deuterium in C2H2⋅ ⋅ ⋅DF by 10% and increases the corresponding H–F bond length by 1%.