The molybdenum trisamidoamine (TAA) complex [Mo] {[3,5-(2,4,6-i-Pr3C6H2)(2)C6H3NCH2CH2N]Mo} carries out catalytic reduction of N-2 to ammonia (NH3) by protons and electrons at room temperature. A key intermediate in the proposed [Mo] nitrogen reduction cycle is nitridomolybdenum(VI), [Mo(VI)]N. The addition of [e(-)/ H+] to [Mo(VI)]N to generate-[Mo(V)]NH might, in principle, follow one of three possible pathways: direct proton-coupled electron transfer; H+ first and then e(-); and then H+. In this study, the paramagnetic Mo(V) intermediate {[Mo]N}- and the [Mo]NH transfer product were generated by irradiating the diamagnetic [Mo]N and {[Mo]NH}(+) Mo(V1) complexes, respectively, with gamma-rays at 77 K, and their electronic and geometric structures were characterized by electron paramagnetic resonance and electron nuclear double resonance spectroscopies, combined with quantum-chemical computations. In combination with previous X-ray studies, this creates the rare situation in which each one of the four possible states of [e(-)/H+] delivery has been characterized. Because of the degeneracy of the electronic ground states of both {[Mo(V)]N}(-) and [Mo(V)]NH, only multireference-based methods such as the complete active-space self-consistent field (CASSCF) and related methods provide a qualitatively correct description of the electronic ground state and vibronic coupling. The molecular g values of {[Mo]N}- and [Mo]NH exhibit large deviations from the free-electron value ge. Their actual values reflect the relative strengths of vibtonic and spin orbit coupling. In the course of the computational treatment, the utility and limitations of a formal two-state model that describes this competition between couplings are illustrated, and the implications of our results for the chemical reactivity of these states are discussed.