Spectrally resolved phosphorescence and slow fluorescence from selected vibronic levels of jet-cooled glyoxal

Trans-glyoxal molecules in a seeded pulsed jet were laser-excited into sele cted vibrational levels of the T-1 and S-1 states. In the latter case, thos e specific rovibrational levels were chosen which exhibit S-1/T-1 gateway c oupling. In each case, the long-lived emission into the S-o state was obser ved employing a spectrograph/CCD combination, covering 5000 cm(-1) at 60 cm (-1) FWHM resolution. A model Franck-Condon calculation of the relative nu (5) band intensities demonstrates the structural similarities of the S-1 an d T-1 states. However, there are some distinct differences, despite the alm ost identical S1 and TI vibrational frequencies. The S-1 <-- S-0 excitation distorts the molecule significantly more in the <nu>(5) dimension than doe s T-1 <--S-0.