Coriolis intensity perturbations of the ν4 band of SF 6
Abstract
In the ν4 band of 32SF 6 the intensity of absorption by the R branch has been found to exceed that of the P branch by 38%. This is substantially larger than the 15% excess that one calculates from ordinary rotational statistics and the nonnegligible width of the band. We attribute this imbalance to Coriolis interactions between the rovibrational sublevels (a) of the ν3 and ν4 excited vibrational states, and (b) of the ground vibrational state and the l = 1 ( F1 g) level of the ν3 + ν4 combination state. The intensities of the observed P- and R-branch lines have a superposed Herman-Wallis type F factor of the form F( m) = (1 + ξ 4m) 2, where m = - J for the P branch, 0 for the Q branch, and +( J + 1) for the R branch, and J is the rotational sublevel in the ground state. We have determined ξ 4 by a new method from the relative intensities of the P, Q, and R branches. New evidence is reported that supports an earlier conclusion that the first derivatives of the dipole moment function, μ 3 = {∂μ}/{∂q 3} and μ 4 = {∂μ}/{∂q 4}, have the same sign. The corresponding Coriolis effect is calculated for UF 6. It is predicted that Coriolis interactions induce weak absorption in the ν6 bands of SF 6 and UF 6, which would otherwise be inactive according to selection rules for strong infrared absorption or Raman scattering. An order-of-magnitude estimate of the absorption intensity of the induced ν6 band of SF 6 agrees with a recent observation of that infrared spectral region.
- Publication:
-
Journal of Molecular Spectroscopy
- Pub Date:
- March 1983
- DOI:
- 10.1016/0022-2852(83)90217-5
- Bibcode:
- 1983JMoSp..98..229P