Low-Frequency Rotational Spectrum of HDO

In the region between 475 and 3500 Mc/sec one P-branch and five Q-branch lines in the spectrum of HDO have been completely measured and identified. These data have contributed materially to an evaluation of the structural constants of the molecule. From the data obtained by this and other microwave spectroscopy projects we have computed the principal moments of inertia, respectively, as having the values of 1.1982, 3.0862, and 4.3887 in units of gm cm2×10—40. In addition, the shape of the 32 → 33 line at 824.64 Mc/sec has been extensively studied. At low pressure the wings of the line have been shown to be wider than is consistent with the Lorentz line shape probably due to the presence of sattelite lines arising from the hyper-fine splitting of the energy levels by the quadrupole moment of the deuteron. The observed effects are consistent with a quadrupole coupling constant of 272±90 kc/sec with respect to an axis along the O–D bond.