Reinterpretation of the electronic absorption spectrum of the methylene amidogen radical (H2CN)

The peculiar electronic absorption spectrum of H2CN has been of great interest to experiment. Herein, this system is studied extensively by applying theoretical methods to the ground and low-lying excited electronic states. Employing a large breadth of high-level ab initio computations, including coupled cluster [CCSD(T) and CCSDT(Q)] and multireference configuration interaction [MRCISD+Q] methods, we comprehensively demonstrate that the most recent experimental and theoretical interpretations of the electronic spectrum of H2CN are in error. The previous assignments of the two broad features in the spectrum as the origin 000 (∼35 050 cm−1) and 402 (∼35 600 cm−1) B 2A1←X 2B2 transitions are both found to be incorrect. The presently reported transition energies suggest that the higher energy band near 35 600 cm−1 is the true origin band. Additionally, from the computed anharmonic vibrational frequencies of the X 2B2 and B 2A1 states, we show that this ∼550 cm−1 band spacing cannot be attributed to a sim...