The elusive formaldonitrone, CH2=N(H)-O. Preparation in the gas phase and characterization by variable-time neutralization-reionization mass spectrometry, and ab initio and density functional theory calculations

Formaldonitrone, CH2=N(H)-O (1), the hitherto elusive simplest organic nitr one, has been prepared transiently in the gas phase by femtosecond collisio nal neutralization of its cation radical, CH2=N(H)-O+. (1(+.)). Ion 1(+.) w as generated by dissociative ionization of 1,2-oxazolidine and characterize d by collisionally activated dissociation mass spectra and augmented Gaussi an 2(MP2) calculations. Nitrone 1 showed negligible dissociation upon colli sional neutralization and was distinguished from its tautomers formaldoxime (2) and nitrosomethane (3). 1 was calculated to be more stable than its is omers CH2-O-NH (5) and oxaziridine (6). The enthalpy of formation of 1 was calculated from enthalpies of atomization and two isodesmic reactions as De lta H-f,H-298(1)=58 +/- 1 kJ mol(-1). The adiabatic and vertical ionization energies of 1 were calculated as IEa=9.40 eV and IEv=9.42 eV, the vertical recombination energy of 1(+.) was REv=9.35 eV. Formation of 1 by collision al electron transfer was accompanied by negligible Franck-Condon effects. T he potential energy surfaces for the formation, isomerizations, and dissoci ations of 1 and 1(+.) were investigated by ab initio calculations.