ROTATIONAL STATE DEPENDENCE OF RADIATIONLESS TRANSITIONS IN S1 PROPYNAL

The rotational state dependence of the radiationless processes of S1 propynal, HC = CCHO, was investigated in three selected vibronic bands located at an excess energy of about 3000 cm-1 in a molecular beam using molecular quantum beat spectroscopy. The number of quantum beat frequencies counted in single rovibronic fluorescence decays shows a clear dependence on the rotational quantum number N of the excited rovibronic singlet state, reflecting an increase of the number of coupling triplet states n(T) by a factor of 4, from N = 0 to 14. This increase is accompanied by a lengthening of the decay lifetimes by a factor of 3. Given eigenstate resolution, the effect of magnetic interactions in the triplet state is discussed and it is concluded that the N dependence is predominantly due to mixing of K states resulting in a symmetry breakdown. This mixing is proposed to be mainly induced by hyperfine interaction via the dipole-dipole term.