FIR LMR SPECTRA OF FO2 - SOME CLASSIC EXAMPLES OF LEVEL ANTICROSSING RESONANCES

Far infrared LMR spectra of FO2 at wavelengths near 920-mu-m have been recorded and analysed. These spectra extend earlier FIR LMR work on the radical to longer wavelengths. Many of the FO2 spectra, including those around 920-mu-m show features that can only be explained by level anticrossing mechanisms. The rotational assignment of several anticrossing spectra was achieved using zero field parameters from a previous mm wave absorption study and g-factors estimated theoretically. The anticrossings involved in the present study derive from operators in the effective Hamiltonian that mix rotational levels with DELTA-N = 0, DELTA-J = 0, +/- 1 and DELTA-K(a) = +/- 1 where N, K(a) are the usual symmetric top quantum numbers and J = N + S. A combined fit of LMR, anticrossing, and millimetre wave spectral data is used to estimate values for some of the parameters describing these effects. Residual differences between the observed and calculated spectra are discussed in terms of possible additional contributions to the effective Zeeman Hamiltonian and further experimental tests to determine the importance of these small terms are suggested.