Dissociation Dynamics Of State-selected Nitrous Oxide And Methyl Bromide Cations

The main work in this thesis contains two aspects:(1) Spectrum investigation and dissociation dynamics of N2O+at B2Π state;(2) Dissociation dynamics of internal energy-selected CH3Br+ion.Pure parent ions, N2O+(X2Π1/2,3/2(000)), were produced by (3+1) REMPI of jet-cooled N2O molecular using a laser whose wavelength is fixed at360.55nm, and were excited to B2Π state by another tunable laser. The photofragment excitation (PHOFEX) spectra were gained by recording signal of NO+fragment while scanning the dissociation laser in the range of278-243nm. Through the analysis of the rotational structures, some spectrum constants such as rotational constants together with spin splitting constants have been obtained and the "band-head" of the B2Π state have been corrected for the first time. Then, the PHOFEX spectra were assigned as N2O+B2Π(viv2v3)←X2Π(000) transition. What’s more, it was found that the width of the TOF spectra of NO+is broadened due to the fragment recoiling after dissociation. The total released translational energies Et at different vibration levels of B2Π state were estimated from the TOF spectra analysis. Under the assistance of potential energy curves of N2O+ion, the dissociation mechanism was proposed:the B2Π state couples to2∑-or2△state through conical intersection, and then dissociate to NO+(X1∑+)+N(2D) products, with high rotational excitation of NO+fragment.Dissociative photoionization of methyl bromide (CH3Br) in an excitation energy range of10.45-16.90eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X2E of CH3Br+is stable, and both A2A1and B2E ionic excited states are fully dissociative to produce the unique fragment ion of CH3+. From TPEPICO3D time-sliced velocity images of CH3+dissociated from specific state-selected CH3Br+ion, kinetic energy release distribution (KERD) and angular distribution of CH33+fragment ion are directly obtained. Both spin-orbit states of Br(2P) atom can be clearly observed in fast dissociation of CH3Br+(A2A1) ion along C-Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH3Br+(B2E) ion. With the aid of the re-calculated potential energy curves of CH3Br+including spin-orbit coupling, dissociation mechanisms of CH3Br+ion in A2A1and B2E states along C-Br rupture are revealed. For CH3Br+(A2A1) ion, the CH3++Br(2P1/2) channel is occurred via an adiabatic dissociation by vibration, while the Br(P3/2) formation is through vibronic coupling to the high vibrational level of X2E state followed by rapid dissociation. C-Br bond breaking of CH3Br+(B2E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.