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

where ; for HD-H, , for HD-He, , and for HD-H_{2} , .
The parameter prevents divergence
of the rate coefficients as .

Four files are included, for de-excitation of HD by H, He, ortho-H_{2} and
para-H_{2}; 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-H_{2},
the level indices, , correspond to the rotational levels of the vibrational ground state of HD, and *J*
= *i* - 1. For HD-para-H_{2} , the
initial and final states are identified by the pair of values of

and , corresponding
to the rotational levels of para-H_{2} and HD, respectively. In this case,
the calculations included both the ground state of para-H_{2}, , and the first excited state, , and the complete set of results is given.