Ab Initio Calculation of H2NO Geometry and Hyperfine Splittings

Abstract

The spin-unrestricted Hartree–Fock (UHF) method has been applied to the H2NO radical, using as basis functions Gaussians centered on the various atoms. The system is found to be nonplanar, with an out-of-plane angle of 26° and an HNH angle of 116°. Bond lengths of 1.34 and 0.99 Å are predicted for the NO bond and the NH bonds, respectively. The nonplanarity of the system is found to be due to the steep slope of the highest occupied orbital (of b1 symmetry and NO antibonding). This last point is in agreement with the prediction of Walsh. As for the other orbitals, little similarity is observed with the Walsh orbital energy diagram. Hyperfine coupling constants have been computed for both N and H atoms, using the UHF wavefunction as well as carrying out a single annihilation and a complete projection. The UHF method provides the most satisfactory results, namely, 11.2 G for N and − 8.8 G for H. These are to be compared with the experimental results (absolute values) of 11.9 G for both atoms. The importance of averaging over vibrational states in indicated.