STUDIES OF RADIATIONLESS TRANSITIONS IN CORONENE USING NANOSECOND LASER PHOTOLYSIS AND SPECTROSCOPY,
TRW SYSTEMS REDONDO BEACH CALIF
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The technique of nanosecond laser photolysis and spectroscopy was used to observe absorption from both the lowest excited singlet S1 and the lowest triplet T1, of coronene. The technique employs a Q-switched ruby laser to produce both a 30 nsec pulse at 347nm for excitation plus, at the same time, a laser-induced spark which provides a background continuum for absorption spectroscopy. New transient absorption bands were observed for coronene at 520 and 380 nm and attribute these to absorption by the S1 state. The new bands locate previously unobserved higher singlet levels of g parity. These bands decay over a period of several hundred nanoseconds and are concomitantly replaced by absorption bands characteristic of the lowest triplet state, thus providing a pictoral record of the process of intersystem crossing. The T-T absorption spectrum of coronene was also obtained in epoxy plastic out to 1.14 microns using a double-beam cross-irradiation technique. New maxima in the infra-red serve to locate the energies of three low-lying excited triplet levels. Coronene intersystem crossing from higher singlet to the triplet manifold may occur.
- Radiation and Nuclear Chemistry