The (Dimethylamino)methyl Radical. A Neutralization-Reionization and ab Initio Study

The (dimethylamino)methyl radical (1) is generated in the gas phase by collisional neutralization of (CH₃)₂N⁺=CH₂(1⁺) with Xe, (CH₃)₃N, and CH₃SSCH₃ and by collisionally activated dissociation of ionized 1,2- bis(dimethylamino)ethane (2) at 8 keV and characterized by neutralization-reionization mass spectrometry. Vertical neutralization of 1⁺ involves large Franck-Condon effects and produces 1 with ≥76 kJ mol⁻¹ excess internal energy. Neutral 1 dissociates by loss of methyl to give CH₃N==CH₂ which undergoes further dissociation upon reionization. In contrast to vacuum pyrolysis, a significant fraction of 1 survives for 3.6 μs to yield 0.6–2.5% 1⁺ after collisional reionization with O₂, ICl, NO₂, and TiCl₄, whereas >25% of 1 survives after collisionally activated dissociation of 2^•+. Equilibrium geometries of 1 and 1⁺ from ab initio calculations with the 6-31G* basis set substantially differ in the C-N bond lengths and pyramidization at N and CH₂. Calculations using the Møller-Plesset theory at the MP4- (SDTQ)/6-31G* and MP4(SDQ)/6-311G** levels with zero-point vibrational energy corrections are used to estimate the relative stabilities of 1, 1⁺, and their ionic and neutral dissociation products. The vertical ionization energies of 1 and C2H5N isomers are calculated and evaluated at the MP2 and MP4/6-311G** levels of theory. Large Franck- Condon effects are predicted by theory and found by experiment in the vertical neutralization of CH₃N==CH2^•+ and aziridine^•+. Stable ^•H₂CNHCH₂^• biradical is prepared by neutralization of ⁺CH₂NHCH₂^• and predicted to be the (¹A₁) singlet electronic state.