ROTATIONAL COHERENCE MEASUREMENTS OF PERYLENE COMPLEXES WITH BENZENE AND NAPHTHALENE - VIBRONIC EXCITATION AND STRUCTURAL RELAXATION

Experiments involving rotational coherence spectroscopy have measured moments of inertia of the jet-cooled 1:1 complex of perylene with naph thalene in the S-1 state. This complex is found to have overlapped rin gs, resembling the 1:1 complex of perylene with benzene. The high rota tional symmetry of the aggregate prevents unambiguous determination of the angle subtended by the molecular long axes. Two possible structur es are therefore suggested, corresponding to parallel and perpendicula r alignment of the molecular long axes. The effects of vibronic excita tion for both the benzene and naphthalene 1:1 complexes of perylene we re also investigated. Electronic-origin excitation of either complex r esults in prominent rotational coherence transients. The signals persi sted with the same amplitude for 353 cm(-1) vibronic excitation of nap hthalene and were still present, at reduced intensity, at 705 cm(-1) T he naphthalene complex shows little or no vibrational coupling for the se excitation energies. On the other hand, vibronic excitation of the benzene complex at greater than or equal to 353 cm(-1) or the naphthal ene complex at 540 cm(-1) showed no rotational coherence signal, both cases signifying the occurrence of vibration-rotation coupling.