Hydrogen Isotopic Substitution Studies of the 2165 Wavenumber (4.62 Micron) “XCN” Feature Produced by Ion Bombardment

The interstellar 4.62 μm absorption band, commonly seen toward embedded protostellar objects, has not yet been unambiguously identified; here we report 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 previous implications of carbon and nitrogen. If the atmosphere of the early Earth was not overly reducing, as some studies indicate, production of prebiotic molecules containing the cyanogen bond would have been difficult. In that case, CN-bearing molecules, necessary for the origin of life, may have come primarily from extraterrestrial sources, and the interstellar medium may be an important source of those molecules. Laboratory studies show that energetic 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 interstellar spectra. Earlier isotopic labeling experiments clearly identified carbon, nitrogen, and oxygen as active participants of the XCN species. In this paper, results of ion bombardment of CH 3 OH : N 2 and CD 3 OD : N 2 ices are presented. A shift in band position resulting from deuterium substitution demonstrates that hydrogen is also a component of the carrier in the laboratory-produced 4.62 μm 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 photolysis experiments.