FURTHER EVIDENCE FOR THE OCN- ASSIGNMENT TO THE XCN BAND IN ASTROPHYSICAL ICE ANALOGS

The well-known ''XCN'' feature near 2167 cm(-1) observed towards vario us low- and high-mass embedded protostars can be well matched with a f eature produced by photolysis of astrophysical ice analogs containing CO and NH3. An assignment of this laboratory XCN band to OCN- was earl ier proposed based on the correspondence in position and in the C-13 a nd N-15 isotopic shifts, We report here a further experimental study o f this identification. First, the isotope shift of the XCN band obtain ed by irradiating O-18 labelled ice samples equals 8.7 +/- 0.6 cm(-1), in good agreement with OCN-. Second, highly sensitive spectroscopy re veals three additional weak features which can be assigned to the OCN- ion. Together with the earlier work, these results leave little doubt to the correctness of the identification of the laboratory XCN featur e with OCN-.