VISIBLE-LIGHT-INDUCED PHOTOCHEMISTRY OF 2,3-DIMETHYL-2-BUTENE.N2O4 CHARGE-TRANSFER COMPLEXES IN SOLID INERT MATRICES AT 75-K

Continuous-wave laser-induced photochemistry of 2,3-dimethyl-2-butene (DMB).s-N2O4 complexes embedded in solid CO2 and solid Xe at 75 K was observed at wavelengths as long as 488 nm (s: symmetric form (O2N-NO2)). The chemistry was monitored by Fourier transform infrared and UV-visible spectroscopy. Products identified by N-15 and O-18 isotope substitution were 2,3-dimethyl-3-nitroso-2-butyl nitrate (major), 2,3-dimethyl-3-nitro-2-butyl nitrite, and a-N2O3 (both minor). A mechanism is proposed that is distinct from that previously suggested for thermal alkene + N2O4 chemistry in solution and liquid N2O4. UV-visible spectra of DMB.s-N2O4, 2-methyl-2-butene.s-N2O4, and trans-2-butene.s-N2O4 complexes in solid CO2 revealed intense new absorptions with maxima at 360, 338, and 296 nm, respectively. These are assigned to charge-transfer transitions. The DMB.s-N2O4 charge-transfer band extends to 550 nm and is responsible for the observed photochemistry.