Vibronically selective intersystem crossing in van der Waals complexes of 9-cyanoanthracene with xenon

Supersonically expanded 9-cyanoanthracene (9CNA) and its van der Waals complexes with xenon have been examined by laser-induced fluorescence excitation spectroscopy. Previously unassigned vibronic features in the spectrum of the bare molecule have been assigned. Measurements of the relative intensities of corresponding vibronic features in the corrected spectra of 9CNA and its 1:1 complex with Xe are used to calculate the quantum yields of fluorescence arising from single vibronic levels at energies in the range 0<Ev<800 cm−1. Variations are attributed to mode selectivity in S1–T1 intersystem crossing.