New insight into dissociative photoionization of N2O at ∼20 eV using threshold photoelectron-photoion coincidence velocity imaging

Dissociative photoionization (DPI) of N2O at ∼20 eV has been reinvestigated with threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. In threshold photoelectron spectrum, a shoulder peak at 20.045 eV is observed close to the ground vibrational level of C2Σ+ state at 20.100 eV. Through comparing the coincident mass spectra recorded at 20.045 and 20.100 eV, the assignment of the shoulder band is corrected to a vibrational excited D2Π ionic state from the previous conclusions of the vibrationless level of b4Π or hot band of C2Σ+ state. For the dominant photofragment of NO+ at 20.045 eV, TPEPICO time-sliced velocity image is measured to obtain the corresponding total kinetic energy and angular distributions. Interestingly, both the bimodal vibrational population and angular distribution of NO+ fragment from dissociation of N2O+(D2Π) are very similar to those of N2O+(C2Σ+) ions. With the aid of potential energy curves, the DPI mechanisms of N2O via D2Π ionic state at 20.045 eV along the NO+(X1Σ+) + N(2D) and NO+(X1Σ+) + N(2P) dissociation channels are clarified, in which the internal conversion from D2Π to B2Π state is the rate-determined step.