Intersystem Crossing of 2-Methlypyrazine Studied by Femtosecond Photoelectron Imaging.

2-methylpyrazine was excited to the high vibrational dynamics of the S 1 state with 260 nm femtosecond laser light, and the evolution of the excited state was probed with 400 nm light. Because it was unstable, the S 1 state decayed via intersystem crossing to the triplet state T 1 , and it may have decayed to the ground state S 0 via internal conversion. S 1 -to-T 1 intersystem crossing was observed by combining time-resolved mass spectrometry and time-resolved photoelectron spectroscopy. The crossover time scale was 23 ps. Rydberg states were identified, and the photoelectron spectral and angular distributions indicated accidental resonances of the S 1 and T 1 states with the 3s and 3p Rydberg states, respectively, during ionization.