Investigations On Ultrafast Dynamics And MATI Spectroscopy Of Several Aromatic Molecules

This dissertation is composed of two parts. One is the investigation on the ultrafast process of dichlorobenzene and chlorotoluene; the other is the investigation on the MATI spectroscopy of deuterium substituted p-methoxyphenol and o-fluorophenol.Photodissociation process of aryl halide is complicated and occurs by a predissociative mechanism. In the first part of this thesis, the dissociation dynamics of o, m, p-dichlorobenzene and o, p-chlorotoluene upon the excitation at 270 nm have been studied in real time directly by using femtosecond pump-probe technique, combined with time of flight (TOF) mass spectrometer. We obtained the time dependence curve of the population in the excited state by delaying the 810 nm probe pulse. The lifetime constants of them are experimentally determined. Possible dissociated mechanisms are suggested that the initially excited S1 state is predissociative via the repulsive triplet state. The substituent effects of additional chlorine atom and methyl group are discussed. Moreover, for the first time, we observe a novel quantum beat oscillation in dichlorobenzene. It indicates that the excitation of a coherent superposition state in some coupled levels occurs during the photodissociation process. We suggest that the observed time dependent behavior may result from rotationally mediated intramolecular vibrational energy redistribution. The beat frequency was determined by fitting with certain model.In the second part, we have recorded the R2PI and MATI spectra of deuterium substituted p-methoxyphenol to investigate the site-specific H/D exchange and isotope effect on transition energy and molecular vibration. The adiabatic ionization energies (IEs) of the four isomers were determined. The H/D exchange...