Photoelectron spectroscopy of CH2N−

We have measured the negative ion photoelectron spectra of CH2N− and CD2N− and find the electron affinities: EA(CH2N)=0.511±0.008 eV and EA(CD2N)=0.498±0.011 eV. Franck–Condon simulations of these spectra are carried out and we estimate the CH2N− and CH2N geometry differences; we fit our spectra with the following [constrained] molecular structures. We combine our EA(CH2N) with the results of previous gas phase ion studies to extract a number of thermochemical parameters (kcal/mol): Do0(CH2N–H)=85±5, Do0(H–HCN)=23±6, Do0(H2C–N)=144±6, and the isomerization enthalpy of H2CN+→HCNH+ is ΔHisom(C2v→C∞v)=−51±7. Attempts to calculate the geometry and vibrational frequencies of the H2CN radical are disappointing. Unrestricted Hartree–Fock and second-order Mo/ller–Plesset ab initio calculations in a 6-31++G** basis produce badly spin-contaminated wave functions which do not reproduce the experimental findings.