Thermal Processing and Interactions of Ethyl Formate in Model Astrophysical Ices Containing Water and Ethanol

Abstract

Temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) have been used to investigate the interactions between ethyl formate and water and ethyl formate and ethanol in model astrophysical ices adsorbed on a graphitic model grain surface. Experiments show that the ethyl formate forms hydrogen bonds to both water and ethanol via the oxygen lone pairs. This leads to the observation of shifts in the vibrational wavenumber of the C═O and C—O—C modes of ethyl formate, which can potentially be used to identify the environment of this complex organic molecule in astronomical observations. TPD data show that the interaction of ethyl formate with water is stronger than that with ethanol with an additional species being observed in the TPD spectrum corresponding to the desorption of ethyl formate directly bonded to the water ice surface. The desorption energy of ethyl formate adsorbed on water ice was found to be 48.5 kJ mol–1, compared to 43.2 kJ mol–1 for pure ethyl formate monolayers. Ethyl formate also traps in water ice and undergoes volcano desorption at the water amorphous to crystalline phase transition temperature. In contrast to the water, ethanol has very little effect on the desorption of ethyl formate with the two species behaving independently even in a codeposited ice.