LABORATORY IDENTIFICATION OF THE 4.62-MU-M SOLID-STATE ABSORPTION-BAND IN THE ISO-SWS SPECTRUM OF RAFGL-7009S

We focus on the problem of the assignment of the ''XCN'' solid stare f eature observed in the spectra of numerous protostellar objects. This feature, located at 4.62 mu m has been tentatively identified with the molecular ion OCN-. New laboratory experiments have been performed in order to confirm this identification. OCN- is produced by UV photolys is of mixtures of CO:NH3 (1 : 1) deposited on a cold substrate. Simult aneously, the counterion NH4+ is also produced to balance the charge i n the matrix. The use of electron donor and acceptor dopants incorpora ted in the mixtures allows us to reduce or enhance the production of t he OCN- and NH4+ features, thus establishing their ionic character. Th e production of HNCO when an electron acceptor is used, and the format ion of the OCN- band during thermal annealing, constitute convincing a rguments in favour of the formation of OCN- and NH4+ by acid-base reac tions where the acid HNCO transfers a proton to the base NH3. We consi der the astrophysical implications for the interpretation of the ISO-S WS spectrum of the protostellar source RAFGL 7009S. In this source, th e 4.62 mu m band is deep and large, although the derived abundance of this ion, relative to H2O ice, is on the order of 4%. Identification o f OCN- is considered in several other sources. The contribution of NH4 + to the unidentified 6.85 mu m feature is discussed.