=== Chemistry files ===
This directory contains several chemistry files.

One of these chemistry files has to be selected in pdr.in
Users should pay attention to :
- modify the elementary abundances 
- select a chemistry file compatible with the ISRF selected in pdr.in (Mathis or Draine)

*** Notations
ch              : chemistry
1606            : 2016 June
iso             : contains isotops 13C and 18O
Mathis / Draine : photo-reactions cross sections provided for Mathis or Draine ISRF

*** References
These chemical networks have been build from different sources :
* OSU database    : http://www.physics.ohio-state.edu/~eric/research.html
* KIDA database   : http://kida.obs.u-bordeaux1.fr
* UMIST database  : http://www.udfa.net
* LAMDA database  : http://www.strw.leidenuniv.nl/~ewine/photo
* several articles

*** Note on some reactions ---------------------------------------------------------------

* H2 collisional dissociation rate: 
  In hot gas, H2 can be dissociated by collisions with H atoms and H2 molecules. 
  This process is an important cooling process in hot gas. Important discrepancies are 
  found in the literature about this rate. Presently, two rates are implemented in the 
  PDR code, Janev et al. (2008) and Glover and Mac Low. (ApJ Supp 2007). The rate to 
  use must be selected commenting and de-commenting the proper lines in PDR_CHEMISTRY.f90 
  (reaction type 110). 
  By default, Janev et al. (2008) is selected. 
  The temperature profile in the hot atomic layer of PDRs can be significantly modified 
  depending on the selected rate. We are investigating the impact of this rate 
  (Le Bourlot et al. in prep) and we may change the default value in the future.



