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Astron. Astrophys. 351, 1066-1074 (1999)

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Carbon dioxide-methanol intermolecular complexes in interstellar grain mantles *

E. Dartois 1,2, K. Demyk 2, L. d'Hendecourt 2 and P. Ehrenfreund 3

1 Institut de Radioastronomie Millimétrique, 300 rue de la piscine, 38406 Saint Martin d'Hères, France
2 Institut d'Astrophysique Spatiale, Bât. 121, Université Paris XI, 91405 Orsay Cedex, France
3 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands

Received 24 March 1999 / Accepted 18 August 1999

Abstract

We present new laboratory data to interpret the Infrared Space Observatory (ISO) spectra of protostellar objects, and particularly RAFGL7009S. Our experimental results show that solid methanol and carbon dioxide exhibit specific intermolecular interactions. We propose the formation of a Lewis acid-base complex between carbon dioxide and methanol molecules to explain specific substructure of the 15.2 µm CO2 bending mode observed in different objects.

The various CO2 bending mode patterns observed in many lines of sight can be interpreted as a combination of both this complex formation and the temperature evolution of the ices. The temperature induced segregation of ice mantles containing CO2 can be monitored by the 13CO2 stretching mode shift toward the pure CO2 ice position. The large width observed for this mode towards interstellar sources partly results from the different temperatures sampled along the line of sight.

Given the amount of methanol involved in RAFGL7009S, on the basis of ground based observations, we derive that about half of the so called "6.85 µm" band and a quarter of the 4.9 µm bands can be accounted for by the deformation modes and 2[FORMULA] transitions of CH3OH.

Key words: ISM: abundances – ISM: individual objects: RAFGL 7009S – infrared: ISM: lines and bands

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA

Send offprint requests to: E. Dartois (dartois@iram.fr)

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© European Southern Observatory (ESO) 1999

Online publication: November 16, 1999
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