Infrared Spectrum of the BrHBr− Ion Isolated in an Argon Matrix

Infrared absorptions assigned to v3, (v3+v1), and (v3+2v1) of BrHBr− have been observed in samples of HBr in an argon matrix which have been subjected to 1216-Å photolysis or which have been co-deposited with an alkali metal atomic beam and then subjected to mercury-arc radiation. The corresponding experiments on deuterium-enriched samples support this identification. Mechanisms by which BrHBr− is produced in these experiments are considered in detail. An atomic mechanism leading to the stabilization of the uncharged species is shown to be inadequate. However, several ionic processes may contribute to the observed production of the anion. As previously postulated, dissociative electron attachment to (HBr)2 may occur. In addition, it is necessary to postulate the production of Br− by various charge-transfer processes, followed by the reaction of Br− with HBr. Analysis of the infrared spectra of BrHBr− and of BrDBr− indicates that the vibrational potential function must include significant contributions from both cubic and quartic terms.