Studies On Excited State Dynamics Of Iodine Ethane And Ionic Spectroscopy Of Aromatic Compounds

Molecular excited state dynamics and ionic spectroscopy are the important components of laser chemistry. Research of excited state dynamics and ionic spectroscopy can help us to obtain more information of the excited states and ionic states of the molecules. Femtosecond time resolution is an important feature of femtosecond time-resolved photoelectron imaging. It makes the real-time investigating of the dynamics of molecules to become a reality. Mass Analyzed Threshold Ionization Spectroscopy (MATI) is a powerful technique for studies of molecular ions and can offer a very high resolution with mass resolved.Excited state dynamics of Iodine ethane has been investigated by femtosecond time-resolved photoelectron imaging. The ionic spectroscopies of3.4-difuoroanisole and m-methoxystyrene have been investigated by mass analyzed threshold spectroscopy. The dissertation is mainly composed of three parts:The first part is the study of ultrafast dynamics of electronically excited states in ethyl iodine using femtosecond timeresolved photoelectron imaging coupled with mass spectroscopy. The dissociation constant of the A band was measured to be about57fs. Upon two400nm photon excitation to the B band, the time evolution of the parent ion with consists of two components. The fast component with a time constant of50fs revealed the energy transfer from the higher Rydberg states to the B band. The slow one was determined to be1.42ps, which was due to predissociation relaxation from the B band to the repulsive A band.The second part is the vibronic and cation spectra of3,4-difluoroanisole recorded by R2PI and MATI techniques. The band origins of the S1S0electronic transition of the cis and trans rotamers appear at35505±2and35711±2cm-1and the adiabatic ionization energies are determined to be67780±5and68125±5cm-1, respectively. We find that there may have an additivity rule associated with the energy shifts in the E1and IE of3,4-difluoroanisole. This rule may be useful for spectroscopists to make an initial guess in setting proper scanning ranges of their lasers for their experiments involving multiple substituted benzenes. Analysis of the obtained vibronic and cation spectra shows that a propensity rule maintaining the same vibration in the D0←S1transition exists. This indicates that the molecular geometry, symmetry, and vibrational coordinates of the cation in the Do state are like those of the neutral species in the Si state for both cisandtransrotamers of3,4-difluoroanisole. In addition, investigations on the frequencies of the active vibrations suggest that the geometry is more rigid in the cationic Do state than that in the neutral S1state.The Third part is the vibronic and cation spectra of m-methoxystyrene recorded by R2PI and MATI techniques. The band origin of the S1←S0electronic excitation for conformer a, b, c, and d of m-methoxystyrene are found to be32767±2,32907±2,33222±2, and33281±2cm-1. And, the adiabatic IE are determined to be65391±5,64977±5,65114±5, and64525±5cm-1, respectively. Analysis on the MATI spectra of m-methoxystyrene and p-methoxystyrene shows that the frequencies of these in-plane ring vibrations depend on the relative location two substituent groups on the aromatic ring as well as the vibrational pattern.