Fourier transform infrared studies of guest-host interactions in ice

Unrestricted Guest-host interactions in amorphous solid water (ASW) films doped with CO2 or N2O were examined experimentally. Investigations focused on exploring molecular transport and morphology in ASW. The main diagnostics were Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD).; ASW films were prepared at 90 K. Dopants exposed to these films saturate all the favorable sites within the film interior. The subsequent accumulation of dopants occurs atop the ASW films, and results in a polycrystalline film. Infrared signatures permit a distinction for these two cases; vibrational modes of the crystalline overlayer, and an easily discernible peak for dopants residing within the ASW film.; Desorption experiments show ASW traps some of the dopants residing within its bulk. As anticipated, some of these trapped species are released during the ASW-to-cubic ice transition at ~160 K. Annealing the 90 K ASW films to 120 K prior to dopant exposure lowers the film's capacity to include dopants within its bulk. No substantial differences were observed for CO2 and N2O. ASW dangling OH bonds displayed a red shift of roughly 50 cm-1 upon interaction with these dopants.; Sandwich structures were prepared at 90 K, i.e., ASW-dopant-ASW. At 105 K, some of the dopant molecules sandwiched in between the ASW escape by diffusion through the top ASW layer, and the remaining molecules appear to be distributed within the ASW film interior.; The factors mediating the ratio of dopants released during the phase transition to dopants that co-desorb with crystalline (cubic) ice were studied. The infrared signatures for these two sets of molecules suggest their local environments are similar. Future experiments using small molecules to explore molecular transport at complex interfaces are outlined.