Electronic Spectra of Polyatomic Molecules

Photodissociation of nitromethane has been investigated for decades both theoretically and experimentally; however, as a whole picture, the dissociation dynamics for nitromethane are still not clear, although many different mechanisms have been proposed. To make a complete interpretation of these different mechanisms, photolysis of nitromethane at 226 and 271 nm under both collisional and collisionless conditions is investigated at nanosecond and femtosecond time scales. These two laser wavelengths correspond to the π* ← π and π* ← n excitations of nitromethane, respectively. In nanosecond 226 nm (π* ← π) photolysis experiments, CH3 and NO radicals are observed as major products employing resonance enhanced multiphoton ionization techniques and time-of-flight mass spectrometry. Additionally, OH and CH3O radicals are weakly observed as dissociation products employing laser induced fluorescence spectroscopy; the CH3O product is only observed under collisional conditions. In femtosecond 226 nm experiments, C...

Photodissociation dynamics of nitromethane at 226 and 271 nm at both nanosecond and femtosecond time scales.

The photochemistry of nitromethane has been studied extensively for many years. Although it is generally agreed that the principal photodissociative process is cleavage of the C−N bond to yield the...

Multiphoton Ionization and Dissociation of Nitromethane Using Femtosecond Laser Pulses at 375 and 750 nm

A mechanism for ignition of high-temperature gaseous nitromethane—The key role of the nitro group in chemical explosives☆

The photolysis and pyrolysis of nitromethane and methyl nitrite have been studied using the techniques of flash photolysis and kinetic spectroscopy. The results show that photolysis of nitromethane yields methyl radicals and nitrogen dioxide, and that these fragments undergo recombination and disproportionation reactions to form methyl nitrite, methoxyl, and nitric oxide. In the presence of added nitric oxide, the methyl radicals react principally with nitric oxide to form nitrosomethane, which subsequently dimerizes and also reacts further with nitric oxide to yield nitrogen dioxide. The evidence also suggests that nitrosomethane is removed by a relatively efficient reaction with nitrogen dioxide at elevated temperatures to produce nitromethane and nitric oxide. In the case of methyl nitrite, light absorption results not only in photolysis, but also in the formation of an isomer of the nitrite which then reverts slowly to the stable form. The nature of this isomer is not known, but possibilities are suggested and discussed. It is concluded that the decomposition (photolytic or pyrolytic) of methyl nitrite occurs by the rupture of the O—N bond, and that the methoxyl radicals formed disproportionate to yield methanol and form aldehyde. Nitroxyl is also formed but only as a minor product, and the marked increase in intensity of its spectrum in the presence of added nitric oxide shows that it is not formed by a molecular elimination reaction, but probably by CH 3 O + NO → CH 2 O + HNO.

Ernst Hirschlaff

Papers

348. Primary photochemical processes. Part IX. A preliminary study of the decomposition of nitromethane and nitroethane