Ortho-Para Conversion in CH3F. Self-Consistent Theoretical Model
  A complete theoretical model of the nuclear spin conversion in 13CH3F induced by intramolecular ortho-para state mixing is proposed. The model contains parameters determined from the level-crossing spectra of the 13CH3F spin conversion. This set of parameters includes the ortho-para decoherence rate, the magnitude of the hyperfine spin-spin interaction between the molecular nuclei and the energy gap between the mixed ortho and para states. These parameters are found to be in a good agreement with their theoretical estimates. 
Pavel L. Chapovsky