Locating and confirming the C-H stretch bands of the halide-acetylene anion complexes using argon predissociation spectroscopy

Abstract

Infrared spectra of Cl - -C 2 H 2 · Ar, Br - -C 2 H 2 · Ar, and I - -C 2 H 2 · Ar are recorded in the C-H stretch region by monitoring production of X - -C 2 H 2 photofragments. Each spectrum exhibits a single band corresponding to the vibration of a hydrogen-bonded C-H unit (v HB = 2882, 2982, 3075 cm -1 for Cl - -C 2 H 2 · Ar, Br - -C 2 H 2 · Ar, I - -C 2 H 2 · Ar, respectively). Marked differences between the spectra of Cl - -C 2 H 2 Ar and Cl - C 2 H 2 are attributable to the strong Cl - -HCCH bond which prevents cold Cl - -C 2 H 2 complexes from dissociating following absorption of an infrared photon. The evidence suggests that addition of the first few Ar solvent atoms has a minor infl..