Collisional excitation of singly deuterated ammonia NH$_2$D by H$_2$
  The availability of collisional rate coefficients with H$_2$ is a
pre-requisite for interpretation of observations of molecules whose energy
levels are populated under non local thermodynamical equilibrium conditions. In
the current study, we present collisional rate coefficients for the NH$_2$D /
para--H$_2$($J_2 = 0,2$) collisional system, for energy levels up to $J_\tau =
7_7$ ($E_u$$\sim$735 K) and for gas temperatures in the range $T = 5-300$K. The
cross sections are obtained using the essentially exact close--coupling (CC)
formalism at low energy and at the highest energies, we used the
coupled--states (CS) approximation. For the energy levels up to $J_\tau = 4_2$
($E_u$$\sim$215 K), the cross sections obtained through the CS formalism are
scaled according to a few CC reference points. These reference points are
subsequently used to estimate the accuracy of the rate coefficients for higher
levels, which is mainly limited by the use of the CS formalism. Considering the
current potential energy surface, the rate coefficients are thus expected to be
accurate to within 5\% for the levels below $J_\tau = 4_2$, while we estimate
an accuracy of 30\% for higher levels.
