Knowledge Bank

Due to intersystem crossing the $S1$ state of naphthalene is coupled to a manifold of triplet states. Therefore part of the excited singlet state molecules will end in the triplet state. We have measured simultaneously the laser induced fluorescence and phosphorescence spectra of several vibronic bands of the $S1\leftarrow S0$ transition in naphthalene in a molecular beam. The phosphorescence was detected by colliding the molecules after excitation on a cold copper surface further downstream. With this set-up, in combination with a single frequency laser rotational resolution was achieved. The resulting spectra correspond to an asymmetric rotor, for which all lines could be identified. We found the intersystem crossing rate to be independent of the rotational quantum numbers and depending on the vibrational state.