Hydrogen isotopic substitution studies of the 2165 wavenumber (4.62 micron) "XCN" feature produced by ion bombardment

The interstellar 4.62 mum absorption band, commonly seen toward embedded pr otostellar objects, has not yet been unambiguously identified; here we repo rt new results which further elucidate the components of the band carrier, which is often referred to in the literature as the "XCN" band due to previ ous implications of carbon and nitrogen. If the atmosphere of the early Ear th was not overly reducing, as some studies indicate, production of prebiot ic molecules containing the cyanogen bond would have been difficult. In tha t case, CN-bearing molecules, necessary for the origin of life, may have co me primarily from extraterrestrial sources, and the interstellar medium may be an important source of those molecules. Laboratory studies show that en ergetic processing of ice mixtures containing H, C, N, and O atoms readily reproduce a band similar in peak position and profile to that seen in the i nterstellar spectra. Earlier isotopic labeling experiments clearly identifi ed carbon, nitrogen, and oxygen as active participants of the XCN species. In this paper, results of ion bombardment of CH3OH:N-2 and CD3 OD:N-2 ices are presented. A shift in band position resulting from deuterium substituti on demonstrates that hydrogen is also a component of the carrier in the lab oratory-produced 4.62 mum band. Irradiation of ices through ion bombardment allows the testing of mixtures which include N-2, a possible source of the available nitrogen in dense cloud ices that cannot be probed through UV ph otolysis experiments.