Interaction of Acetonitrile with Alcohols at Cryogenic Temperatures

Temperature-dependent interaction of acetonitrile with methanol and ethanol, as codeposited and sequentially deposited films, was studied in the 10–130 K window, in ultra high vacuum. Films in the range of 50–100 monolayers were investigated using temperature-dependent reflection–absorption infrared spectroscopy (RAIRS), Cs+ ion scattering mass spectrometry, and temperature-programmed desorption (TPD). Acetonitrile interacts with methanol and ethanol through intermolecular hydrogen bonding. When a codeposited system was annealed, acetonitrile underwent a phase segregation at 110 K, and large changes in the infrared spectrum were observed. The OH stretching of methanol gave two peaks characteristic of the change to the α-phase of methanol, while ethanol gave three peaks at the same temperature. The surface composition of the systems probed by 40 eV Cs+ scattering showed that both the alcohols and the acetonitrile were of equal intensity below 110 K, while above 110 K the intensity of the latter went down s...