# Analytic fits to the rate coefficients

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

,

where ; for HD-H, , for HD-He, , and for HD-H2 , .     The parameter   prevents divergence of the rate coefficients as .

Four files are included, for de-excitation of HD by H, He, ortho-H2 and para-H2; these files are called, respectively, qh1hd.dat , qhehd.dat , qoh2hd.dat and qph2hd.dat. In each file, the first line specifies the total number of transitions.  Subsequent lines contain, in successive columns: indices identifying the initial (upper) state and the final (lower) state; the values of the a, b, and c.  For HD-H, HD-He, and HD-ortho-H2, the level indices, , correspond to the rotational levels of the vibrational ground state of HD, and J  =  i  - 1.  For HD-para-H2 , the initial and final states are identified by the pair of values of

and , corresponding to the rotational levels of para-H2 and HD, respectively.  In this case, the calculations included both the ground state of para-H2, , and the first excited state, , and the complete set of results is given.