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E.F. van Dishoeck - F.P. Helmich - Th. de Graauw - J.H. Black - A.C.A. Boogert - P. Ehrenfreund - P.A. Gerakines - J.H. Lacy - T.J. Millar - W.A. Schutte - A.G.G.M. Tielens - D.C.B. Whittet - D.R. Boxhoorn - D.J.M. Kester - K. Leech - P.R. Roelfsema - A. Salama - B. Vandenbussche
We present searches for gas-phase CO2 features in the ISO-SWS infrared spectra of four deeply embedded massive young stars, which all show strong solid CO2 absorption. The abundance of gas-phase CO2 is at most 2 . 10 -7 with respect to H2 , and is less than 5% of that in the solid phase. This is in strong contrast to CO, which is a factor of 10-100 more abundant in the gas than in solid form in these objects. The gas/solid state ratios of CO2 , CO and H2 O are discussed in terms of the physical and chemical state of the clouds.
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