  Many atmospheres (cool stars, brown dwarfs, giant planets, extrasolar
planets) are predominately composed of molecular hydrogen and helium.
H$_2{}^{16}$O is one of the best measured molecules in extrasolar planetary
atmospheres to date and a major compound in the atmospheres of brown-dwarfs and
oxygen-rich cool stars, yet the scope of experimental and theoretical studies
on the pressure broadening of water vapour lines by collision with hydrogen and
helium remains limited.
  Theoretical H$_2$- and He-broadening parameters of water vapour lines
(rotational quantum number $J$ up to 50) are obtained for temperatures in the
range 300 - 2000 K. Two approaches for calculation of line widths were used:
(i) the averaged energy difference method and (ii) the empirical expression for
$J$\p $J$\pp-dependence.
  Voigt profiles based on these widths and the BT2 line list are used to
generate high resolution ($\Delta \tilde{\nu}$ = 0.01 \cm) pressure broadened
cross sections for a fixed range of temperatures and pressures between 300 -
2000 K and 0.001 - 10 bar. An interpolation procedure which can be used to
determine cross sections at intermediate temperature and pressure is described.
Pressure broadening parameters and cross sections are presented in new ExoMol
format.
