Publication
- Names
-
- J. Noble
- Title
- The desorption of H2CO from interstellar grains analogues
- Abstract
- Context. Much of the formaldehyde (H2CO) is formed from the hydrogenation of CO on interstellar dust grains, and is released in the gas phase in hot core regions. Radio-astronomical observations in these regions are directly related to its desorption from grains. Aims: We study experimentally the thermal desorption of H2CO from bare silicate surfaces, from water ice surfaces and from bulk water ice in order to model its desorption from interstellar grains. Methods: Temperature-programmed desorption experiments, monitored by mass spectrometry, and Fourier transform infrared spectroscopy are performed in the laboratory to determine the thermal desorption energies in: (i.) the multilayer regime where H2CO is bound to other H2CO molecules; (ii.) the submonolayer regime where H2CO is bound on top of a water ice surface; (iii.) the mixed submonolayer regime where H2CO is bound to a silicate surface; and (iv.) the multilayer regime in water ice, where H2CO is embedded within a H2O matrix. Results: In the submonolayer regime, we find the zeroth-order desorption kinetic parameters ν0 = 1028 mol cm-2 s-1 and E = 31.0 +/-0.9 kJ mol-1 for desorption from an olivine surface. The zeroth-order desorption kinetic parameters are ν0 = 1028 mol cm-2 s-1 and E = 27.1 +/-0.5 kJ mol-1 for desorption from a water ice surface in the submonolayer regime. In a H2CO:H2O mixture, the desorption is in competition with the H2CO + H2O reaction, which produces polyoxymethylene, the polymer of H2CO. This polymerization reaction prevents the volcano desorption and co-desorption from happening. Conclusions: H2CO is only desorbed from interstellar ices via a dominant sub-monolayer desorption process (E = 27.1 +/ - 0.5 kJ mol-1). The H2CO which has not desorbed during this sub-monolayer desorption polymerises upon reaction with H2O, and does not desorb as H2CO at higher temperature.
- Keywords
- astrochemistry, molecular processes, ISM: molecules, molecular data
- Content
- thermodynamic data use
- Year
- 2012
- Journal
- Astronomy and Astrophysics
- Volume
- 543
- Number
- A5
- Pages
- 1 - 9
- Pages number
- 9
- Document type
- article
- Publication state
- published
- Doi
- 10.1051/0004-6361/201219437
- Identifiers
-
- URL:
- bibcode: