Adsorption and photochemistry of multilayer bromoform on ice

The adsorption and photochemistry of bromoform multilayers on and in amorphous solid water (ASW) are studied using reflection absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), and time-of-flight (TOF) techniques. Regardless of the initial exposure, bromoform resides on top of the ASW layer. No migration of bromoform molecules into the ASW film is observed for adsorption on top of the water layer. UV irradiation at a wavelength of 266 nm results in significant desorption of photochemical fragments, reaction of photochemical products on the surface and light-induced molecular reorganization of the remaining CHBr₃, which is apparent from a comparison of pre- and post-irradiation TPD experiments. The ice-mediated C-C (C₂H₂Br₂) and C-O (CHBrO) photoproducts desorb from both the ASW surface and the Pt surface. The photoproduct C₂H₂Br₄ is formed exclusively from multilayers of CHBr₃ and desorbs only from the Pt surface.