Direct observation of hydrogen atom adducts to nitromethane and methyl nitrite. A variable-time neutralization-reionization mass spectrometric and abinitio/RRKM study

Variable-time neutralization-reionization mass spectrometry was used to gen erate elusive radicals CH3NO2H. (1), CH3O(H)-NO. (2) CH3O-N(H)-O-. (3), and CH3O-N-OH. (4) that represent hydrogen atom adducts to nitromethane and me thyl nitrite, respectively. Radicals 1, 3, and 4 were stable species on the 3.7 us time scale of the experiment. Radical 2 dissociated completely to C H3OH and NO. The major unimolecular dissociations of 1 formed CH3NO + OH. a nd CH3. + NO2H, whereas loss of H-. to form CH3NO2 was insignificant. Gauss ian 2(MP2) and density functional theory calculations provided the structur es and bond dissociation energies of 1-4. The relevant parts of the potenti al-energy surface were used for RRKM and transition-state theory calculatio ns of unimolecular dissociation kinetics. The calculated branching ratios f or 1 were in accord with experiment. The unimolecular chemistry of radicals 1-4 formed by femtosecond collisional electron transfer can be accounted f or by the properties of the ground electronic states of 1-4.