J. M. Greenberg

Cosmic ray induced explosive chemical desorption in dense clouds

The desorption due to the energy release of free radicals in the ice mantles of a dust grain is investigated theoretically by calculating the ultraviolet radiation field inside the cloud, the free radical accumulation, the cosmic-ray heating of the grain and then the desorption in this situation starting from the cosmic-ray energy spectra. This model can reproduce the observations of the CO gas abundances and level of depletion in dark clouds such as L977 and IC 5146 with a combination of input parameters which are either constrained by independent observations or have been derived independently from laboratory experiments. We investigate other desorption mechanisms and conclude that they cannot explain the observations. The model also shows that the energy input by the cosmic-ray induced ultraviolet field is almost one order of magnitude larger than the direct energy input by cosmic-ray particles. This strengthens the conclusion that desorption due to the energy release by ultraviolet photon produced radicals dominates over direct cosmic-ray desorption.

Possible detection of solid formaldehyde towards the embedded source GL 2136

We present new medium resolution spectroscopy (λ/Δλ≊1000) between 3.37 and 3.66 μm towards the deeply embedded source GL 2136. Besides an absorption feature at 3.535 μm due to solid CH3OH which was ealier observed towards other embedded sources, a new feature is apparent at 3.477 μm. From comparison with laboratory data of low temperature ices, we tentatively assign this feature to solid formaldehyde. Our dats combined with earlier observations of CO and H2O indicate towards GL 2136 an ice composition of H2O : CH3OH : H2CO : CO =100 : 3.6 : 2.5 : 3.0.

Formaldehyde and Methanol Dominated Ices Toward GL 2136

Infrared spectroscopy towards the embedded massive protostellar object GL 2136 reveals 2 absorption features at 3.47 and 3.54 µm. Through comparison with spectra of laboratory ice mixtures, an identification with, respectively, the v 5 feature of solid formaldehyde and a blend of the v 1 formaldehyde and the v 3 solid methanol mode is proposed. Detailed comparison with a variety of ice mixtures indicates that the methanol and formaldehyde ice on one hand and water ice on the other reside, for the greater part, in separate phases.