Direct Observation of Hydrogen Atom Adducts to Nitromethane and Methyl Nitrite. A Variable-Time Neutralization−Reionization Mass Spectrometric and ab Initio/RRKM Study

Abstract

Variable-time neutralization−reionization mass spectrometry was used to generate 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 methyl nitrite, respectively. Radicals 1, 3, and 4 were stable species on the 3.7 μs time scale of the experiment. Radical 2 dissociated completely to CH3OH and NO. The major unimolecular dissociations of 1 formed CH3NO + OH• and CH3• + NO2H, whereas loss of H• to form CH3NO2 was insignificant. Gaussian 2(MP2) and density functional theory calculations provided the structures and bond dissociation energies of 1−4. The relevant parts of the potential-energy surface were used for RRKM and transition-state theory calculations of unimolecular dissociation kinetics. The calculated branching ratios for 1 were in accord with experiment. The unimolecular chemistry of radicals 1−4 formed by femtosecond collisional electron transfer can be accounted for by the properties of the ground electronic s...