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Astron. Astrophys. 346, 990-994 (1999)

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The infrared band strengths of CH3OH, NH3 and CH4 in laboratory simulations of astrophysical ice mixtures

O. Kerkhof, W.A. Schutte and P. Ehrenfreund

Raymond and Beverly Sackler Laboratory for Astrophysics at Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands

Received 16 March 1999 / Accepted 20 April 1999


Results from groundbased observations and the Infrared Space Observatory (ISO) indicate that CH3OH, NH3 and CH4 are important constituents of interstellar ice mantles. In order to accurately calculate the column densities of these molecules, it is important to have good measurements of their infrared band strength in astrophysical ice analogs. Band strength measurements of CH3OH and CH4 are presented showing that they depend only weakly on the composition of the ice matrix and the temperature. On the other hand, the umbrella mode of NH3 does show a significant decrease when dilluted in H2O ice. For this reason the original estimates of the abundance of NH3 in interstellar ice need to be revised upward by 30%.

Key words: methods: laboratory – ISM: abundances – ISM: dust, extinction – ISM: molecules – infrared: ISM: lines and bands

Send offprint requests to: W.A. Schutte (schutte@strw.leidenuniv.nl)

© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999