The functional fit to the rate coefficients for collisional de-excitation takes the
form

where , and a value of was adopted in all the fits. This last parameter prevents divergence of the rate coefficients as .

Three files are included, for de-excitation of para-H_{2} and ortho-H_{2}
(merged into a single file) by H, He, ortho- and para-H_{2}; these files are
called, respectively, qh1h2.dat
, qheh2.dat , qoh2h2.dat and qph2h2.dat In each
file, the first line specifies the total number of transitions. Subsequent lines
contain, in 5 successive columns: an index identifying the initial (upper) state; an index
identifying the final (lower) state; value of a; value of b; value of c. The
ordering (and identification) of the levels is according to energy, commencing with the
lowest *J*=0, *v*=0 state of H_{2}. For transitions induced by
collisions with H, He, and para-H_{2}, the 49 lowest energy levels are all
included, i.e. up to and including *J*=6, *v*=3. In addition, levels 52 (*J*=7,
*v*=3) and 54 (*J*=8,*v*=3) are present, as they were incorporated in the
collisional basis sets. For transitions induced by collisions with ortho-H_{2},
a smaller basis of 39 energy levels was used. The energetic ordering of the
pairs of values of (*J*,*v*) is to be found in the file: labelling.energy_levels