Ab initio molecular orbital calculation of the HONO torsional potential

Abstract

Ab initio SCF-MO calculations were performed to obtain a torsional potential function for the HONO molecule. Calculations were made for the cis and trans conformations with the STO-3G, 4-31G, 6-31G, 4-31G*, and 6-31G** basis sets. Complete geometry optimization was carried out within each basis set. It was found that the 4-31G basis set provided values for the geometry and energies closest to the experimental results. The trans-cis isomeric energy difference was calculated to be -0.642 kcal/mol and the energy barrier to rotation from trans to cis was found to 9.68 kcal/mol; the comparable experimental energies are -0.6 and 9.7 kcal/mol, respectively. Completely optimized geometries using the 4-31G basis set were used to calculate a detailed torsional potential. These points were fit with a cosine series.