Number density ratio of ortho and para varieties of
H2 as collision partner. The default (o/p=0) is to use the
thermal value at the kinetic temperature, assuming that only the J=0
and J=1 levels are populated. The overestimate of the true
o/p ratio is at most 20% (at T=155 K).
This parameter only matters when separate rate coefficients exist for
collisions with ortho and para H2. For the
moment, this is only the case for CO, OH and H2O.
Last modified: May 12, 2004