Photoionization of DABCO via high vibrational levels of the S1 state

The photoelectron spectrum following resonant two-photon ionization of 1,4-diazabicyclo[2.2.2]octane (DABCO) was recorded with the laser tuned to the origin band of the S2←S0 transition. The spectrum is consistent with the rapid radiationless transition from the S2 state into high vibrational levels of the S1 state, as proposed by Smith et al. [J. Phys. Chem. 88 (1984) 2250]. Features in the double-resonance spectrum of Smith et al. that were previously assigned to photoionization of S(−) 3s(−)1A″2 vibrational levels populated by a radiationless transition from the S2 state are reinterpreted, with the conclusion that the S(−) state has yet to be observed.