Infrared spectra of proton irradiated ices containing methanol

A set of experimental results on the spectral identification of new species synthesized in irradiated CH3OH and H2O+CH3OH ices is reported. Mass spectroscopy of volatile species released during slow warming gives supporting information on identifications. H2CO is the dominant volatile species identified in the irradiated ices; CH4, CO and CO2 are also formed. During warming the ice evolves into a residual film near 200 K whose features are similar to those of ethylene glycol along with a CO bonded molecular group. Irradiation simulates expected cosmic ray processing of ices in comets stored in the Oort cloud region for 4.6 billion years. Results support the idea that a comet originally containing an H2O+CH3OH ice component has a decreasing concentration of CH3OH towards its outer, most heavily irradiated layers (if independent of all other sources and sinks). The CH4CO and COCO2 ratios are calculated as a function of irradiation; after 22 eV per molecule, CH4CO = 1.96 and COCO2 = 1.45 in an H2O+CH3OH ice mixture. Infrared spectra of CH3OH at T < 20 K on amorphous silicate smokes show a predominantly crystalline phase ice. Irradiation of the ice/silicate composite is compared with irradiated CH3OH on aluminum substrates. Implication for cometary type ices are discussed.