Theoretical study of the electronic structure of diazomethane

The least-energy dissociation path of the ground state of CH₂N₂ was determined fromab initio calculations using in a complementary way basis sets of minimal size (STO-3G) and double-zeta (DZ) quality. The results indicate that the least-energy point of attack of the N₂ molecule on CH₂ (¹A₁) is roughly perpendicular to the molecular plane (93 °), the C and N atoms being almost co-linear (angle C-N-N203 ° with outermost N atom pointing away from CH₂). The potential barrier of 1.2 eV found previously on theC_2v dissociation path, disappears completely along the least-energy dissociation path (point groupC_s (out-of-plane)). These findings corroborate the Woodward-Hoffman rules for this process since the outermost orbitals of the two intersecting states found in point groupC_2v (...2b₁ and ...8a₁) both correlate to the same irreducible representation (10á) in point groupC_s (out-of-plane).Larger basis set calculations (DZ + polarization functions on all centers, 3d_c and 3d_N developed here), were also carried out on CH₂N₂ (¹A₁,³A₂ and¹A₂) at the¹A₁ equilibrium geometry and on CH₂ (³B₁) and N₂ (¹_g⁺) at their respective equilibrium geometries. These calculations, together with consideration of correlation energy differences, yieldD₀⁰ (CH₂N₂,¹A₁) = 19 kcal/mole and vertical excitation energies of 67 and 73 kcal/mole for the³A₂ and¹A₂ states respectively. The latter value is in good agreement with the measured experimental value: 72.4 kcal/mole corresponding to the maximum of intensity in the¹A₂¹A₁ absorption band.