LASER-EXCITED FLUORESCENCE FROM S-TRIAZINE VAPOR - ANALYSIS OF VIBRONIC COUPLING PATHWAYS

Resolved fluorescence from s-triazine vapour is observed after exciting the first strong absorption band in the 320 nm (1E ←1A'1) electric dipole forbidden absorption system. The fluorescence spectrum is relatively simple, in contrast with the complex structure seen in absorption. In emission, intensity is induced principally by the e' ring distortion, v6, appearing as the vibronic origins 610 and 612. This mirrors the activity in vapour absorption, but other significant vibronic origins seen in absorption are of greatly reduced importance in 61 fluorescence. Long progressions in the symmetric ring breathing mode v12 are built on progression origins, giving information on the Franck-Condon development which in absorption is obscured by congestion. The observed vibronic activity confirms that the 320 nm absorption arises largely due to coupling between a 1E″ state, and a higher 1A″2 state, but there is evidence that other mechanisms may also be important. © 1979.