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

Supersonically expanded 9-cyanoanthracene (9CNA) and its van der Waals comp lexes with xenon have been examined by laser-induced fluorescence excitatio n spectroscopy. Previously unassigned vibronic features in the spectrum of the bare molecule have been assigned. Measurements of the relative intensit ies 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 fluore scence arising from single vibronic levels at energies in the range 0 < E-v < 800 cm(-1). Variations are attributed to mode selectivity in S-1-T-1 int ersystem crossing. (C) 2001 Elsevier Science B.V. All rights reserved.