Photodissociation mechanism of nitramide: a CAS-SCF and MS-CASPT2 study

The complete active space self-consistent field (CAS-SCF) method combined with the multistate second-order perturbation theory (MS-CASPT2) are used to study the low-lying, singlet and triplet, potential energy surfaces of nitramide. Vertical transition calculations have allowed us to reinterpret the gas-phase UV spectrum of nitramide as the overlapping of two intense bands calculated at 6.46 and 6.52 eV, respectively. The states of relevance in its photochemistry after excitation at different wavelengths have been determined to be up to S4. From that point on, the most probable dissociation mechanism is determined by considering relative energies among the different stationary points and the major role played by conical intersections connecting S3/S2, S2/S1, and S1/S0 electronic states. The most likely dissociation products are NH2(1(2)B1), NO2(1(2)A1), NO2(1(2)A2), NO2(1(2)B2), NO2(1(2)A1)*, NH2NO(1(1)A''), NO(X(2)pi), and O(1D). With regards to the influence of triplet states in the photodecomposition of nitramide, our calculations indicate that T1/S0 crossing is probable only after radiationless deactivation.