  The hydrogen deuteride (HD) molecule is an important deuterium tracer in
astrophysical studies. The atmospheres of gas giants are dominated by molecular
hydrogen, and simultaneous observation of H$_2$ and HD lines provides reliable
information on the D/H ratios on these planets. The reference spectroscopic
parameters play a crucial role in such studies. Under thermodynamic conditions
encountered in these atmospheres, the spectroscopic studies of HD require not
only the knowledge of line intensities and positions but also accurate
reference data on pressure-induced line shapes and shifts. Our aim is to
provide accurate collision-induced line-shape parameters for HD lines that
cover any thermodynamic conditions relevant to the atmospheres of giant
planets, i.e., any relevant temperature, pressure, and perturbing gas (the
H$_2$/He mixture) composition. We perform quantum-scattering calculations on a
new highly accurate ab initio potential energy surface, and we use scattering
S-matrices obtained this way to determine the collision-induced line-shape
parameters. We use the cavity ring-down spectroscopy for validation of our
theoretical methodology. We report accurate collision-induced line-shape
parameters for the pure rotational R(0), R(1), and R(2) lines, the most
relevant HD lines for the investigations of atmospheres of the giant planets.
Besides the basic Voigt-profile collisional parameters (i.e. the broadening and
shift parameters), we also report their speed dependences and the complex Dicke
parameter, which can influence the effective width and height of the HD lines
up to almost a factor of 2 for giant planet conditions. The sub-percent-level
accuracy, reached in this work, considerably improves the previously available
data. All the reported parameters are consistent with the HITRAN database
format, hence allowing for the use of HAPI for generating the beyond-Voigt
spectra of HD.
