FORBIDDEN TRANSITIONS IN DIATOMIC MOLECULES: V. THE ROTATION–VIBRATION SPECTRUM OF THE HYDROGEN-DEUTERIDE (HD) MOLECULE

The 1–0, 2–0, and 3–0 rotation–vibration bands of HD have been observed with a PbS infrared grating spectrometer and the 3–0 and 4–0 bands have been photographed with a 21-ft concave grating spectrograph. From these spectra precise values of the vibrational and rotational constants of HD in its electronic ground state have been determined. The variation of Bv and ΔG with v is similar to that recently established for H2, that is, the values for v = 0 and 1 are markedly above the values corresponding to a linear extrapolation of the subsequent points. This leads to an uncertainty in the ωe and Be values which is much greater than that of the ΔG and Bv values. The (very low) intensity of the rotation–vibration spectrum of HD is in close agreement with that predicted. The decrease of intensity in going from 1–0 to 4–0 is strikingly slow, far slower than in a normal series of fundamental and overtone bands. This also is in qualitative agreement with theoretical expectation for a molecule like HD which does not have a dipole moment in its equilibrium position.