The interstellar 4.62 micron band

We present new 4.5-5.1 mu m (2210-1970 cm(-1)) spectra of embedded protosta rs, W33 A, AFGL 961 E, AFGL 2136, NGC 7538 IRS 9, and Mon R2 IRS 2, which c ontain a broad absorption feature located near 4.62 mu m (2165 cm(-1)), com monly referred to in the literature as the "X-C=N" band. The observed peak positions and widths of the interstellar band agree to within 2.5 cm(-1) an d 5 cm(-1), respectively. The strengths of the interstellar 4.62 mu m band and the ice absorption features in these spectra are not correlated, which suggests a diversity of environmental conditions for the ices we are observ ing. We explore several possible carriers of the interstellar band and revi ew possible production pathways through far-ultraviolet photolysis (FUV), i on bombardment of interstellar ice analog mixtures, and acid-base reactions . Good fits to the interstellar spectra are obtained with an organic residu e produced through ion bombardment of nitrogen-containing ices or with the OCN- ion produced either through acid-base reactions or FUV photolysis of N H3-containing ices.