DFT and theoretical kinetics studies on the reaction of nitrate radical with α-pinene and β-pinene

The potential energy surfaces for the reactions of α-pinene and β-pinene with NO3 radicals are explored by using M06-2X hybrid meta density functional theory (HMDFT) method. On the basis of the optimized geometries and energies of the intermediates and transition states, the mechanisms of the title reactions are explained and the importance of different product channels is discussed. It is found that pinonaldehyde and NO radical is the most important products of the α-pinene + NO3 reaction. The major products of the β-pinene + NO3 reaction are predicted to be 10-pinenyl radical, nitric acid, 6,6-dimethylbicyclo[3.1.1]heptan-2-one, NO radical and formaldehyde. Variable Reaction Coordinate-Transition State Theory (VRC-TST) is used to compute the overall rate coefficients as a function of temperature. The computed rate constants are compared with the available experimental data.