H, C, N, and O isotopic substitution studies of the 2165 wavenumber (4.62 micron) "XCN" feature produced by ultraviolet photolysis of mixed molecularices

To better understand the chemical species that gives rise to the 2165 cm(-1 ) (4.62 mum) "XCN" absorption feature seen toward embedded protostars such as W33A, we have performed laboratory studies using deuterium (H-2) isotopi c labeling. We report the observation of a small but significant deuterium isotope shift for the "XCN" peak which demonstrates that the atomic motion( s) causing the "XCN" band in the laboratory samples must involve hydrogen. We also report the results of C-13, N-15, and O-18 labeling experiments tha t are consistent with previously reported values.