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

Dissociative photoionization (DPI) of N2O at similar to 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 C-2 Sigma(+) 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 D-2 Pi ionic state from the previous conclusions of the vibrationless level of b(4)Pi or hot band of C-2 Sigma(+) 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+(D-2 Pi) are very similar to those of N2O+(C-2 Sigma(+)) ions. With the aid of potential energy curves, the DPI mechanisms of N2O via D-2 Pi ionic state at 20.045 eV along the NO+(X-1 Sigma(+))+N(D-2) and NO+(X1 Sigma+)+N(P-2) dissociation channels are clarified, in which the internal conversion from D-2 Pi to B-2 Pi state is the rate-determined step. (C) 2014 Elsevier B.V. All rights reserved.