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.