Temperature-programmed desorption and reflectance absorption infrared spectroscopy of H2O:HBr thin films of varying stoichiometry from <1:1 to 5:1

Temperature-programmed desorption (TPD) and reflection absorbance infrared spectroscopy (RAIRS) were used to study H2O:HBr thin films of varying stoichiometry from <1:1 to 5:1. These films were deposited on a Ag(110) crystal at T = 100 K. The TPD data showed a single desorption peak near 180 K in the H2O+ (mle = 18) mass channel for all of the films investigated. In the HBr+ (mle = 82) mass channel, a single desorption peak near 180 K was observed for films with a H2O:HBr stoichiometry greater than or equal to 3:1, indicating sublimation of the H2O:HBr film. For films with a H2O:HBr stoichiometry <3:1, HBr desorption began at temperatures as low as 125 K. The HBr desorption peak was broad and continuous until the entire H2O:HBr film desorbed near 180 K. RAIR spectra of the H2O:HBr films were also recorded as a function of film temperature. The infrared data in conjunction with TPD allowed for changes in the spectra to be interpreted in terms of changes in film crystallinity and film composition.