15min:

JOCHEN KÜPPER, Heinrich-Heine-Universität, Institut für Physikalische Chemie und Elektrochemie I, 40225 Düsseldorf, Germany; TIMOTHY M. KORTER AND DAVID W. PRATT, University of Pittsburgh, Department of Chemistry, Pittsburgh, PA 15260, USA.

The electronic spectrum of indole and its sensitivity to the surrounding environment continues to attract much attention. We report here studies of the rotationally resolved electronic spectra of several vibronic bands of indole and indole( H₂O) in a molecular beam, up to an energy of 990 cm^-1 above the electronic origin of the ¹L_b~state at 35231.525~ cm^-1 (~284~nm). We find, as did Berden, et al. for the 0⁰₀ band, that the vibronic bands exhibit ``anomalous'' line intensities, evidencing axis tilting on S₁ excitation. The degree of tilt is different for different bands, showing that the S₁ \longleftarrow S₀ optical transition moment orientations are also different. We derive from careful analyses of these data information about ¹L_a--¹L_b state mixing in the isolated molecule and its dependence on displacements along different vibrational coordinates. We also show that complexation of indole with one water molecule significantly influences the degree of this mixing.