Photodesorption

28/11/2011

CO ice photodesorption yield

The CO ice photodesorption yield, defined as the number of desorbed molecules per incident photons, has been measured by three groups. The default value in ProDiMo is based on the experiment of Oberg et al. (ApJ 662, L23, 2007). The yield of 2.7e-3 is disputed. Recent experiments (Munoz-Caro et al. A&A 522, A108 2010) and Fayolle et al. (ApJ 739, L36 2011) suggest a much higher value of 3.5e-2 molecules/incident photon. In addition, Fayolle et al. experiment shows the wavelength-dependence of the desorption yield.

The default value is kept at 2.7e-3. The higher value can be used by setting the optional-switch to .true. (switch valid from revision 37f96510):

.true.     ! COphotodesorption_yield2010

28/11/2011

Photodesorption rate decrease due to gas absorption in the UV

Strong H2, C, and H2O (gas) absorption in the UV can shield the ice from absorbing photons that can lead to photodesorption. A preliminary option to take the gas-shielding into account is available (default false), valid from revision 37f96510:

.true.     ! gas_shielded_photodesorption

22/11/2012

Photodesorption yields

Individual photodesorption yields may be known better than the default values encoded in ProDiMo. There is the alternative of providing the photodesorption yield in the column A of the Reactions.in file. If the entry for A is non-zero, it is assumed that A is the desorption yield. If A is zero, the default treatment hardcoded in ProDiMo will be applied to that particular reaction.

8/11/2012

Ice photodesorption from Radiative Transfer

CO ice photodesorption spectrum and yield have been measured by a few laboratory groups. By default, ProDiMo will use a scaled Draine field to compute the CO photodesorption rate. From revision e3cb4265, the users can choose to use the actual CO ice photodesorption cross-section ,measured by Lu et al. 2005 (see also Fayolle et al. 2011):

.true. ! ice_photodesorption_from_RT

ProDiMo will compute a correction due to the fact that the attenuated UV field inside a disk does not has the shape of the Draine UV field.

Reference

  • Fayolle et al. 2001 ApJ, 739, L36
  • Lu et al. J. 2005 Phys. B.: ay. Mol. Opt. Phys., 38, 3693
  • Bertin et al. 2012 Phys. Chem. Chem.Phys, 14, 9929