Sub-collision hyperfine structure of nonlinear-optical resonance with field scanning

Some experimental evidences for methane are produced that the simple transition from frequency scanning of nonlinear-optical resonances to magnetic one may be accompanied with transition from sub-Doppler collisionally broadened structure to sub-collision hyperfine one. It is conditioned by nonlinearity of splitting of hyperfine sublevel for molecules in the adiabatically varied magnetic field and respectively breaking the analogy of magnetic and frequency scannings. The exact calculation of the resonance structure is considered for molecules with only one spin subsystem. The approximately spin-additive calculation of the structure is given for sufficiently fast rotating molecules with greater number of spin subsystems. Within the same approximation an example of hyperfine doubling in the magnetic and electric spectra of nonlinear-optical resonance is considered for fluoromethane.Comment: 56 pages, 10 figures, accepted for publication in J. Mol. Spectrosc

Theory of nuclear spin conversion in ethylene

First theoretical analysis of the nuclear spin conversion in ethylene molecules (13^CCH4) has been performed. The conversion rate was found equal approx. 3x10^{-4} 1/s*Torr, which is in qualitative agreement with the recently obtained experimental value. It was shown that the ortho-para mixing in 13^CCH4 is dominated by the spin-rotation coupling. Mixing of only two pairs of ortho-para levels were found to contribute significantly to the spin conversion.Comment: 20 pages, 5 eps figure