Hyperfine level dependence of pressure broadening in molecular spectra

The hyperfine dependence of collisional relaxation of molecular spectra is a not widely known effect which can be observed only under particularly fav orable circumstances. While the absence of such an effect was observed for various molecules, a variation of the collisional broadening parameter with the hyperfine quantum number F was observed only for CH3I. All these resul ts are explained in the frame of a theoretical model showing that a hyperfi ne F-dependence of the relaxation parameters is not due to the negligible i nfluence of nuclear spin interaction on the collisional dynamics, but to th e F-dependence of the matrix elements of the multipole of the absorber invo lved in the collisional relaxation of the line. A recent experimental inves tigation allows an accurate validation of the theoretical model. (C) 2 001 Elsevier Science B.V. All rights reserved.