Studies On Ultrafast Nonadiabatic Dynamics Of Excited Carbon Disulfide And Para-difluorobenzene

Ultrafast nonadiabatic dynamics of electronically excited molecules plays an important role in photo-reaction, life science and environmental science. The nonadiabatic deactivation processes of electronically excited molecules in the gas phase are all closely related to radiationless deactivation processes of electronically excited molecules during the chemical reactions, including internal conversion, intersystem crossing, intramolecular vibrational energy redistribution, dissociation, isomerization, and so on. Femtosecond time-resolved photoelectron/photoion imaging coupled with time-resolved mass spectroscopy allows for the real-time observation and trace of nonadiabatic deactivation processes of electronically excited molecules in the gas phase. As a result, ultrafast nonadiabatic dynamics of electronically excited molecules has been one of the most active subjects of current reaction dynamics. In this dissertation, three types of small molecules are selected and these nonadiabatic deactivation processes are investigated. The dissertation is organized as follows:The first part is the investigation on the dynamic evolution of CS24d and6s Rydberg wave packet components. Following a two-photon267nm excitation, a Rydberg wave packet is created within the4d and6s Rydberg manifolds of carbon disulfide. All the spin-orbit states of the4d and6s Rydberg states are coherently excited to form the four components of the Rydberg wave packet. The lifetime of the Rydberg wave packet is determined to be about830fs. The temporal evolution of the four components of the prepared Rydberg wave packet is directly observed as time-dependent changes of the intensities of different parts in the main photoelectron peak. Furthermore, time-resolved photoelectron angular distributions clearly reflect the different component characters of4d and6s molecular orbitals, indicating that the initial component of the Rydberg wave packet is mainly in the4d orbital character and the component representing a main characteristic of the6s orbital is remarkably enhanced with the delayed time.The second part is the investigation on intramolecular vibrational energy redistribution dynamics in the S1low-energy regime of the para-difluorobenzene..Para-difluorobenzene has served as an excellent aromatic prototype system for studying IVR. The simplest prototype system for IVR is Fermi resonance. Only the Fermi resonance51…62and the61vibrational state are excited within our excitation wavelength at267nm. The vibrational energy transfer between the two Fermi resonance components of51and62is clearly demonstrated by the time dependence of the photoelectron spectra as well as the corresponding photoelectron angular distributions. And the oscillation period for the vibrational energy transfer is estimated to be less than20ps.The third part is the study of ultrafast internal conversion dynamics of furan. Furan is excited into its S2state by two photons of405nm. The ultrafast internal conversions from S2to both the S1state and the S3state are clearly observed from the time-dependence of the photoelectron spectra.The fourth part is focused on the detailed introduction of the liquid photoelectron spectroscopy of liquid microjet. As an outstanding novel method, liquid photoelectron spectroscopy has recently become possible by virtue of the development of the vacuum liquid microjet technique. The historical overview, the principle, applications and significance of this liquid photoelectron spectroscopy are demonstrated. The prospects and research directions for the liquid PES are also reviewed and discussed.