Dissociation Dynamic Of CF₃Cl⁺ Studied With Threshold Photoelectron-photoion Coincidence Velocity Imaging

The main research work in this thesis includes:Some new image processing methods developed by Matlab programming and graphical user interface on the basis of original ion velocity image processing methods; Dissociation dynamic of CF3Cl* ions studied with threshold photoelectron-photoion coincidence velocity imaging; and the experimental results of CH3F'revealed from threshold photoelectron-photoion coincidence velocity imaging.In the velocity map imaging experiments, the fragment ions flied in the TOF tube, and the images were recorded by CCD camera. In addition, the pulsed high voltage needed to be applied to MCP in the time-sliced velocity image experments. All the electric-field distribution in the TOF tube, the installation position of CCD camera and the width of slices had some influence on the images, so it was required to take some methods to process the images. Some new image processing methods were developed to process the images, including adjusting the image distortion and correcting the branching ratio, by Matlab programming and graphical user interface on the basis of original ion velocity image processing methods.Fluorochloromethane is an important chemical molecule in the atmospheric environment. Under the ultraviolet irradiation, the Cl atom had a great effect on ozone depletion. Compared with the research on neutral molecules, the ionic dissociation mechanism and distribution of fragment ions' energy states were reported rarely so far. Aim at the needs of research on the dissociation dynamics of this sort of molecular ions, the dissociation dynamic of CF3Cl+ ions were studied with threshold photoelectron-photoion coincidence velocity imaging. Specific content as follows:Dissociation of energy selected CF3Cl+ ions in the excitation energy range of 12.10-18.30 eV was investigated by using threshold photoelectron-photoion coincidence velocity imaging. TPEPICO time-of-flight mass spectra and time-sliced velocity images of CF3+ from CFCl+ ions was recorded. The mass spectra indicated that ground state X2E of CF3Cl+ was a bound state with a shallow potential well along the C-Cl bond rupture, only producing CF3+ fragments above the dissociation limit. All the A2A1/B2A2, C2E and D2E ionic excited states were fully dissociative, and two fragment ions, CF3+ and CF2CP, were observed. The CF3+ ions were dominant in the A2A1/B2A2state. However, both CF3+ and CF2Cl+ ions were evident in the C2E, D2E state. From TPEPICO time-sliced velocity images of CF3-, toal kinetic energy release distributions (total KERD) in dissociation and angular distribution of CF3- ions were obtained. In the Franck-Condon region, total KERD obtained in dissociation of CF3Cl- (X2E) ions satisfied the Maxwell-Boltzmann distribution. For CF3Cl-(A2A1/B2A2, C2E and D2E) ions, all the total KERDs included two parts:statistical dissociation and fast/nonstatistical dissociation. With the aid of calculated potential curves of CF3Cl- along C-Cl bond, the dissociation mechanisms of CF3Cl- (X2E, A2A1/B2A2, C2E and D2E) along C-Cl bond rupture are raised. The CF3Cl- (X2E) ions in the high vibrational level statistically dissociated to CF3++Cl. The CF3Cl+ (A2A1/B2A2) ions dissociated in three parts:The CF3Cl- (B2A2) ions directly dissociated along the repulsive C-Cl coordinate; one part of CF3Cl+(A2A1) ions first coupled to the repulsive state nearby, then fast dissociated; the other part of CF3Cl+ (A2A1) ions first converted to the lower X2E state, then statistically dissociated to CF3- fragment ions. Both C2E and D2E state of CF3Cl+ first converted to the lower electronic states via internal internal conversion, then statistically dissociated or rapidly dissociated along the lower electronic states potential energy surface.In the excitation energy range of 12.30-19.80 eV, dissociation of energy selected CH3F+ ions was also investigated by using threshold photoelectron-photoion coincidence velocity imaging. Both H-loss path and F-loss path of CH3F+ were observed. The TPEPICO time-of-flight mass spectra indicated that ground state X2E of CH3F+ was a bound state, mainly producing CH2F+ fragments above the dissociation limit. Both A2A1 and B2E ionic excited states were fully dissociative, and CH3+ ions were dominant in the A2A1, B2E state. From TPEPICO velocity images of CH2F+ and CH3+, toal kinetic energy release distributions (total KERD) in dissociation and angular distribution of CH3+ ions were obtained. However, the potential energy curves for H-loss dissociation and F-loss dissociation were not calculated, and the dissociation mechanisms of H-loss path and F-loss path of CH3F+ has yet to be further discussed in subsequent research work.