Ab initiocalculation of the line strengths in the electric dipole vibration-rotation spectrum of the HD molecule

The perturbation theory expression for the HD molecule vibration-rotation dipole-transition probabilities is cast into the form of an instantaneous dipole-moment function $D\left(R\right)\mathrm{}$. Two large components of $D\left(R\right)\mathrm{}$ can be obtained from accurately known ground-electronic-state expectation values, whereas the rest is computed by a sum-over-states procedure similar to the one we used previously for the dynamic polarizability of ${\mathrm{H}}_2$. From this $D\left(R\right)\mathrm{}$ we compute dipole-transition matrix elements for the 0-0 through 6-0 vibrational bands, for all $P$ and $R$ branch lines with $J_i\le 3$. Our results agree well with the recent calculations of Wolniewicz [Can. J. Phys. 53, 1207 (1975); 54, 672 (1976)]. They also agree well with experiment for the 1-0 through 5-0 bands, but, like the results of Wolniewicz, are a factor of approximately $\surd 2$ larger than the 0-0 band results of M. Trefler and H. P. Gush [Phys. Rev. Lett. 20, 703 (1968)].