High-J rotational spectrum of toluene in |m| ⩽ 3 torsional states

Abstract The study of the rotational spectrum of toluene (C 6 H 5 CH 3 ) is considerably extended to include transitions in | m | ⩽ 3 torsional states up to the onset of the submillimeter wave region. New data involving torsion–rotation transitions up to 336 GHz were combined with previously published measurements and fitted using the rho-axis-method torsion–rotation Hamiltonian. The final fit used 50 parameters to give an overall weighted root-mean-square deviation of 0.69 for a dataset consisting of 8924 transitions with J up to 94 and K a up to 50. The new analysis allowed us to resolve all problems encountered previously for m  = 0 transitions beyond a certain combination of quantum numbers J and K a when many lines of appreciable intensity and unambiguous assignment deviated from the distorted asymmetric rotor treatment. Those discrepancies are now identified to result from m  = 0 ↔  m  = 3 and m  = 0 ↔  m  = −3 resonances, which have been successfully encompassed by the current fit. At the same time an analogous problem was discovered and fitted for m  = 2 transitions, which were found to be affected by many m  = 1 ↔  m  = 2 resonances.