Nitromethyl radical, cation, and anion.: A neutralization and electron photodetachment-reionization mass spectrometric and ab initio computational study of [C,H2,N,O2] isomers

Nitromethyl radical (1) was generated in the gas phase by collisional electron detachment from the stable anion CH2NO2- (1(-)) and characterized by neutralization-reionization mass spectrometry. Radical 1 was stable on the 3.7 mus time scale. Laser electron photodetachment was also used to generate 1 and probe it by collisional reionization and mass spectrometry in a new experiment denoted as -PR+MS. The heat of formation of 1 was obtained by G2(MP2) and G2 calculations of enthalpies of atomization, isodesmic, and dissociation reactions as 126 kJ mol(-1), in excellent agreement with the value from CCSD(T)/aug-cc-pVTZ calculations, DeltaH degrees (f,298)(1) = 127 kJ mol(-1). The dissociation energy of the C-H bond in nitromethane was calculated as 425 kJ mol(-1). No stable structure was found for singlet cation 1(+) in accord with complete dissociation of vertically ionized 1(+). Several anionic, radical, and cationic isomers of the general formula [C,H-2,N,O-2] were identified by ab initio calculations and investigated experimentally. CH2ONO. (2) was generated transiently from the stable cation 2(+) and found to dissociate completely to CH2O and NO on the 3.7 mus time scale. Radical 2 is bound by only 2 kJ mol(-1). Gas-phase deprotonation of methyl nitrite and N-hydroxyformamide, and fluoride anion-induced desilylation of (CH3)(3)SiCH2ONO produced anions with the O-CH=N-OH- (4(-)) and/or O=CH-NH-O- (5(-)) structures that were used to generate stable radicals 4 and/or 5. Collisional neutralization of stable O=C-NH-OH+ (6(+)) formed transiently radical 6 that dissociated exothermically to CO and HNOH.. Cations 4(+) and 6(+) were found to partially interconvert following collisional ionization of radicals 4 and 6.