H2 formation

The default model for v2.0 (i.e if the flag is not present) for H2 formation in ProDiMo is Cazaux & Tielens (2002,2004). In 2010, Cazaux and Tielens published an erratum (ApJ 715, 698). In the new implementation, H2 is formed even more efficiently at warm temperatures. The Cazaux & Tielens model contrasts with the old standard formulation of H2 formation (Jura; Hollenbach).

To use the Cazaux 2010 model, you need for put in Parameter.in

.true.    ! H2_Cazaux2010

To use the Jura-Hollenbach model, you need for put in Parameter.in

.true.   ! H2_Jura

The rate of h2 formation has profound effects on other abundances: C+/C/CO because of the H2/C mutual shielding and because CO is formed after H2 is formed OH/H2O because OH is form by O +H2 and H2O by OH+H2.

Please keep in mind the uncertainties in chemical abundances due to the various H2 formation formalisms.

2022/05/27

For very advanced users, one can use the formation of H2 directly from the (warm and cold) surface chemistry network (see Thi et al. 2020 Astronomy & Astrophysics, Volume 634, id.A42, 28 pp., DOI: 10.1051/0004-6361/201731746). The user has to carefully setup a consistent species, reaction files and use the appropriate flags. Please contact the developers if you wish to use this mode for H2 formation.