Ab initio and density functional study of azidoacetone

The structure, ionisation energies and vibrational spectrum of azidoacetone (N₃CH₂COCH₃) have been calculated using ab initio and density functional methods. We have carried out calculations for two conformers of acidoacetone (anti and gauche). Calculations for the singly ionised structure (N₃CH₂COCH⁺₃) are also reported. The predicted energy difference between the anti and gauche conformer of azidoacetone has been calculated at several different theoretical levels and our best estimation for this barrier is 1.6 kcal mol^-1. Ab initio (HF and MP2) ionisation energies based on Koopmans' theorem are in good agreement with recent photoelectron spectroscopy (PES) measurements. Density functional ionisation energies from highest occupied orbital energies are very dependent on the exchange-correlation potentials and are lower than the experimental values. However, density functional ionisation energies calculated by taking ground-state energy differences are in very good agreement with experimental results. Vibrational frequencies are in good agreement with experimental data for azidoacetone and related molecules.