Studies On Internal Conversion Of Benzyl Chloride And N,N-Dimethylforma Mide

Ultrafast dynamics of electronically excited molecules plays an important role in photo-reaction, life science and environmental science. The study of internal conversion (IC) is an important part of the research of ultrafast dynamics of electronically excited molecules. Femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy, which allows for the real-time observation and track of dynamic processes of electronically excited molecules is an efficiently tool for understanding the internal conversion dynamics. In this dissertation, Benzyl Chloride and N,N-Dimethylformamide molecules are selected and these internal conversion processes are investigated. The dissertation is organized as follows:For the first part, the ultrafast internal conversion of Benzyl Chloride was studied. Upon absorption of two400nm photons, benzyl chloride was excited to the S4and the S2state at the same time. Within50fs, the molecule electronically relaxes from the S4and S2states into the S1state through IC and from there, decayed to the So ground state with the relatively slow time constant of910fs. By the analysis of the changes of photoelectron angular distribution, the coupling time scale of benzyl chloride from the S4state to the S2state is determined to be within25fs.The second part is the investigation of the internal conversion of N,N-Dimethylformamide. The population of S2(ππ*) state undergoes ultrafast internal conversion to the highly vibrationally excited S1(nπ*) state within99fs by very fast C-N stretching, while nonradiative deactivation of the S1(nπ*) state occurs in2.8ps and is to a large extent due to the C-N bond cleavage from the S1potential energy surface, which would be able to efficiently compete with the internal conversion of S0←S1through S1/S0conical intersections.