| Summary: | 碩士 === 國立清華大學 === 化學系所 === 106 === We studied the ultrafast electron transfer (ET) dynamics in the cations of 2-phenylethyl-N,N-dimethylamine (PENNA) after photoionization using the femtosecond pump-probe photoionization-photofragmentation (fs-PIPF) spectroscopy compared our experimental results with these reported by the Schlag's group. We photoionized PENNA in a supersonic beam with fs pump pulses at 265.9 nm with 1+1 REMPI via its S1 origin using the phenyl group as the chromophor, producing PENNA cation predominately in its first excited state (D1). The resulting PENNA cations were then probed by a second fs pulse at ~800 nm by exciting the evolving ionic system to higher excited states, which enhance the fragmentation yield of the cation. We used a consecutive reaction kinetics model including three time steps to fit the parent ion depletion transient signals, and the results are τ_1≈ 0.15 ps, τ_2≈ 18 ps and τ_3≈ 56 ps. To identify which one corresponds to the ET reation, we also carried out similar experiments for 2-phenylethylalcohol (PEAL), 2-phenylethyl-N-methylamine (MPEA) and 2-phenylethylamine (PEA). The results show that PENNA+, MPEA+ and PEA+ transients all contain a sub-ps component that is not observed in PEAL+ transient. For this reason, we attributed the sub-ps time constant to the the ET reaction. The two time constants we used to fit the PEAL+ transient are like the τ_2 and τ_3 in PENNA+, MPEA+ and PEA+, and are assigned to the conformational relaxations from the cation FC state to the most stable conformation.
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