Knowledge Bank

The $S0\leftrightarrow S1$ fluorescence spectra of styrene have been studied experimentally and assigned with the aid of an ab-initio calculation. The vibronic structure of the transition was largely maintained in styrene clusters with rare gases and with ammonia, for in-plane modes. The spectral shifts and the relative intensities were unchanged by comparison with the bare molecule. The out-of-plane $(a\prime \prime )$ modes were influenced differently by the cluster formation- there relative intensity was largely reduced, and some of them were difficult to observe over the noise level. This behavior is consistent with a structural model for the cluster that predicts the smaller molecule to be positioned above the molecular plane. The styrene-ammonia in-plane vibronic transitions were all shifted $52cm-1$ to the blue from the bare styrene lines. Single vibronic level fluorescence (SVLF) recorded from these lines showed great similarity to the corresponding bare molecule SVLF spectra, up to the dissociation energy. Excitation of the styrene-ammonia cluster slightly above the dissociation energy led to an emission spectrum practically identical with that of styrene excited at the 0,0 band, showing a complete dissociation on the excited state potential surface. Excitation of higher bands led to emission from several bare styrene levels simultaneously. Excitation of low lying out-of-plane modes of the styrene-ammonia cluster S1 level showed much weaker lines, consisting of small progressions, suggesting strong coupling between the van der Waals vibrations and the molecular out-of-plane vibrations.