A combination of experimental and quantum chemical results has been used to characterize dimethylfuroxan, (CH3)(2)C2N2O2, isolated in a matrix of solid Ar atoms at 12 K, and then to study its photoinduced isomerization and decomposition. The less-stable isomer 2,3-dinitrosobut-2-ene can be generated by UV photolysis (lambda(max) = 254 nm). However, this species is photolabile and decomposes upon prolonged photolysis times with light having lambda(max) = 254 nm or with IR radiation (lambda(max) = 700 nm) to give CH3CNO as the final, photostable product. The two photoproducts were characterized using a combination of experimental and quantum chemical results. The work presented herein sheds light on the physical and chemical properties of furoxans, which may gain considerable importance as a source of NO, which itself plays a significant role as a biological messenger.