Electronic Splitting between the 2B1 and 2A1 States of the NH2 Radical

Abstract

Theoretical calculations are reported for the ground and first excited states of NH₂. A contracted Gaussian basis of four s, two p, and one d functions is centered on the nitrogen atom, while for hydrogen two s and one p functions are used. Both self‐consistent‐field (SCF) and multiconfiguration first‐order wave‐functions have been computed, the latter using the iterative natural‐orbital method. Two new theoretical ideas were tested and found useful: (a) Bunge's partitioning of degenerate spaces and (b) a procedure for generating uniform sets of starting orbitals for multiconfiguration calculations. For the ²B₁ state the SCF, CI, and experimental geometries are θ=105.4°, r=1.019 Å; θ=102.7°, r=1.055 Å; $\text{θ = 103.3± 0.5}$ , $\text{r=1.024± 0.005 Å}$ . The analogous results for the ²A₁ state are θ=141.9°, r=0.997 Å; θ144.7°, r=1.010 Å; $\text{θ = 144± 5}$ , $\text{r=0.97–1.00 Å}$ . For the upper ²A₁ state the barrier to linearity is 1370 cm⁻¹ in the SCF approximation, 1030 cm⁻¹ from the correlated wavefunctions, and $\text{770± 100\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ experimentally. The ²B₁—²A₁ splitting T_e is predicted to be 12 800 cm⁻¹ (SCF) and 14 500 cm⁻¹ (CI), whereas the experimental value is thought to be $\text{∼ 11\hspace{0.17em}000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ . Potential curves are shown and electronic structure considerations discussed.