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 stoic hiometry 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 th e H2O+ (mle = 18) mass channel for all of the films investigated. In the HB r+ (mle = 82) mass channel, a single desorption peak near 180 K was observe d for films with a H2O:HBr stoichiometry greater than or equal to 3:1, indi cating sublimation of the H2O:HBr film. For films with a H2O:HBr stoichiome try <3:1, HBr desorption began at temperatures as low as 125 K. The HBr des orption peak was broad and continuous until the entire H2O:HBr film desorbe d near 180 K. RAIR spectra of the H2O:HBr films were also recorded as a fun ction of film temperature. The infrared data in conjunction with TPD allowe d for changes in the spectra to be interpreted in terms of changes in film crystallinity and film composition.