Computational experiments on the lowest two electronic states of the N ₂H₃ radical

Abstract

The most accurate computational study to date of the hydrazyl radical N2H3 has resolved previous ambiguities in the lowest energy ground state conformation, showing it to have a nonplanar arrangement of the nuclei, derivable from a planar structure by depressing the NH2 group by approximately 28°. This structure is derived after complete geometry optimization using a "double zeta plus polarization" first-order configuration interaction wave function with 1771 configuration state functions. Other structures studied with this same wave function give the following information about the lowest two potential energy surfaces for this radical. The ground state inversion barrier about nitrogen is small, with a computed value of 0.5 kcal/mole. Rotation is shown to be the lowest energy path for interconversion between equivalent ground state structures; a rotational barrier of 24.9 kcal/mole being computed. An optimized structure for the alternative transition state, with a linear N-N-H arrangement, lies 51 kcal/mole above the lowest energy ground state structure. Vertical excitation requires 4.32 eV, to a point lying 2.95 eV above the minimum on the excited state surface. The f number for the transition is 0.0066. Nuclear relaxation following excitation changes the geometry to a symmetric perpendicular structure in which the NNH plane of symmetry bisects the NH2 group. The minimum on the second potential energy surface is shown to be a point of intersection for symmetric perpendicular 2A″ and 2A′ states. © 1979 American Institute of Physics.