Fluorescence and intersystem crossing as a function of rotational energy on the S1 state of benzene

The effect of rotational excitation on the electronic relaxation of the S₁ state of “isolated” benzene has been studied by examination of resonance fluorescence generated when narrow-band exciting light is swept through the rotational envelopes of four S₁ ← S₀ absorption bands. To within the ten percent uncertainty in measurement, the fluorescence yields are independent of the position of the exciting light within an absorption band. Thus neither radiative decay nor intersystem crossing to the triplet state displays large sensitivity to molecular rotation, at least when excited state relaxation proceeds from rotational distributions of moderate diversity.