Spectroscopic characterization of the ground and low-lying electronic states of Ga ₂N via anion photoelectron spectroscopy

Anion photoelectron spectra of Ga2 N- were measured at photodetachment wavelengths of 416 nm (2.978 eV), 355 nm (3.493 eV), and 266 nm (4.661 eV). Both field-free time-of-flight and velocity-map imaging methods were used to collect the data. The field-free time-of-flight data provided better resolution of the features, while the velocity-map-imaging data provided more accurate anisotropy parameters for the peaks. Transitions from the ground electronic state of the anion to two electronic states of the neutral were observed and analyzed with the aid of electronic structure calculations and Franck-Condon simulations. The ground-state band was assigned to a transition between linear ground states of Ga2 N- (X ¹∑ _gg ⁺) and Ga2 N (X ²∑ _u ⁺), yielding the electron affinity of Ga2 N, 2.506±0.008 eV. Vibrationally resolved features in the ground-state band were assigned to symmetric and antisymmetric stretch modes of Ga2 N, with the latter allowed by vibronic coupling to an excited electronic state. The energy of the observed excited neutral state agrees with that calculated for the A Πu2 state, but the congested nature of this band in the photoelectron spectrum is more consistent with a transition to a bent neutral state.