Irradiation of either pyrazine-2,6-d2 ( 1-2,6-d2) or pyrazine-2,3-d2 (1-2,3-d2) in the vapor phase at 254 nm resulted in the formation of pyrimidine-2,4-d2 ( 2-2,4-d2) and pyrimidine-4,5-d2 ( 2-4,5-d2). Irradaiton of pyrazine-2,5-d2 ( 1-2,5-d2) in the vapor phase led, however, to pyrimidine-4,6-d2 (2-4,6-d2) and pyrimidine-2,5-d2 (2-2,5-d2). These results are consistent with a mechanism involving 2,6-bonding, nitrogen migration, and rearomatization.