Proximity effect in spin sublevel dynamics: Possible influence of a low-lying3 A2 (nπ*) state: On singlet → triplet intersystem crossing of Pyrimidine

Comparison of spin sublevel population rates in pyrimidine and 5-methylpyrimidine suggests that the vibronic perturbation of 3B2 and/or 3A1 ππ* states by a higher-lying 3A2nπ* state plays an important role in S1 → T1 intersystem crossing of pyrimidine. The result also implies that the n+π*—n−π* splitting in pyrimidine is significantly smaller than the corresponding gap in pyrazine. The appearance of the 0.0 band in the τx spectrum indicates that the triplets state symmetry is lower tha C2v.