Laser Excited Emission Spectroscopy of Azulene in the Gas Phase

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Abstract
In this paper we present the results of an experimental study of the radiative decay of the two lowest singlet states S1 and S2 of the azulene molecule in the gas phase excited by a Q switched ruby laser (14 400 cm−1) and by its second harmonic (28 800 cm−1). Spectroscopic information has been obtained concerning the energy resolved spectra of the S1 → S0 and of the S2 → S1 emission. The quantum yield data for the S1 → S0 decay led to an estimate of the nonradiative decay time of S1. The branching ratio between the S2 → S0 and the S2 → S1 emissions was utilized for the evaluation of the S2 → S1 radiative decay time. The study of the consecutive two photon S0 → S1 → S2 excitation leads to an estimate of the S1 → S2 absorption cross section near the electronic origins of the two excited states. The decay characteristics of the lowest excited singlet state of the ``isolated'' azulene molecule confirm the theoretical prediction concerning nonradiative electronic relaxation in the statistical limit.