Theoretical study of the photodetachment spectrum of the methylene amidogene anion (H2CN-).

The excited states of methylene amidogen (H2CN) have recently been studied extensively both by experiment and theory. However, the assignment of absorption spectra is in disagreement with the theoretical analysis. In the present study a theoretical photoelectron detachment spectrum is predicted which shows that a corresponding experiment could be suitable to decide whether the theoretical or the experimental assignment is correct. To this end, the electron affinity of H2CN was calculated very accurately. Vertical and adiabatic electron detachment energies were calculated by complete active space and multi-configuration self-consistent field (CASSCF and MCSCF) as well as by multireference configuration interaction (MRCI) methods. The MRCI wave functions were utilized to compute electronic detachment probabilities. Beyond the radical ground state, three significant detachments are found in the region around 4-5 eV and a further weak detachment at roughly 8.4 eV. Vibrational intensities were determined for the four lowest electronic states of the radical and vibrationally resolved photodetachment spectra were constructed. The predicted spectra show that the bands of the first 2B1 and 2A1 states are clearly distiguishable while the band for the nearby second 2B1 state is weak and strongly overlapping with the 2A1 manifold.