The $J=0\ensuremath{\rightarrow}1$ rotational transition of P${\mathrm{H}}_{3}$ has been measured at ${\ensuremath{\nu}}_{0}=266944.0\ifmmode\pm\else\textpm\fi{}1.0$ Mc/sec ($\ensuremath{\lambda}=1.12$ mm). With ${D}_{J}=3.15$ Mc/sec from infrared spectroscopy, this measurement yields ${B}_{0}=133478.3$ Mc/sec. Similarly, the 0\ensuremath{\rightarrow}1 transition of P${\mathrm{D}}_{3}$ was measured at ${\ensuremath{\nu}}_{0}=138937.98\ifmmode\pm\else\textpm\fi{}0.30$ Mc/sec ($\ensuremath{\lambda}=2.16$ mm) and ${B}_{0}=69470.41$ Mc/sec was obtained by using ${D}_{J}=0.71$ Mc/sec from infrared spectroscopy. The bond lengths in the two isotopic forms were found to be slightly different with ${d}_{\mathrm{PH}}=1.4206\ifmmode\pm\else\textpm\fi{}0.005$ A and ${d}_{\mathrm{PD}}=1.4166\ifmmode\pm\else\textpm\fi{}0.005$ A.

From measurements on the 0\ensuremath{\rightarrow}1 transition of DBr at 1.18-mm wavelength the following information has been obtained: Values of $\ensuremath{\alpha}$ obtained from infrared spectroscopy by Keller and Nielsen were employed in calculating the equilibrium values.

Pure rotational transitions of ${\mathrm{H}}_{2}$${\mathrm{S}}^{32}$, ${\mathrm{H}}_{2}$${\mathrm{S}}^{33}$, and ${\mathrm{H}}_{2}$${\mathrm{S}}^{34}$ have been measured with high precision in the region of one to two millimeters. From these measurements the SH bond length is found to be 1.3226A and the bond angle to be 92\ifmmode^\circ\else\textdegree\fi{} 6\ensuremath{'}. The ${\mathrm{S}}^{33}$ nuclear quadrupole coupling observed along the principal inertial axes are $\mathrm{eQ}{q}_{\mathrm{aa}}=\ensuremath{-}32$ Mc/sec, $\mathrm{eQ}{q}_{\mathrm{bb}}=\ensuremath{-}8$ Mc/sec, and $\mathrm{eQ}{q}_{\mathrm{cc}}=+40$ Mc/sec. Approximate analysis of the quadrupole coupling constants shows that the bonding orbitals of S are $\mathrm{spd}$ hybrids and yields a value of -0.06\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$ for the quadrupole moment of the ${\mathrm{S}}^{33}$ nucleus. From the known ratio $\frac{{Q}^{33}}{{Q}^{35}}$ this gives ${Q}^{35}=0.04\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$. Zeeman studies show that the molecular ${g}_{J}$ factor is approximately, but not exactly, equal for different rotational states. A mean value of 0.24 nuclear magneton is found for ${g}_{J}$.