1 Time-resolved Photoelectron Spectroscopy and the Photoprotective Properties of Adenine

Time-resolved photoelectron spectroscopy (TRPES) is used to measure electronic excited state lifetimes in the DNA base adenine. A detailed description of our femtosecond (fs) laser system, gas-jet molecular beam source, and photoelectron photoion coincidence (PEPICO) spectrometer is given. Ion mass spectra and photoelectron kinetic energy spectra are presented for adenine excitation by 251 nm and ionization by 200 nm. Koopmans’-like ionization correlations are compared to photoelectron spectra, and the states S2(*) and S1(n*) are identified as participating in the electronic relaxation. We determine that the initially excited S2(*) state quickly (1 = 71 ± 16 fs) decays to populate the S1(n*) state, followed by a slow decay to S0(2 = 950 ± 50 fs). Our experiments are in good basic agreement with previously reported experiments.