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Ultrafast Imaging of electronic relaxation in Ortho-xylene： New Features from Fragmentation-Ion Spectroscopy

Chinese Physics Letters 2014年第12期31卷 130-133页

作者：刘玉柱 KNOPP Gregor 肖韶荣 GERBER Thomas College of Physics and Opto-electronics Engineering Nanjing University of Information Science & Technology Nanjing 210044 Paul Scherrer Institute Villigen 5232 Switzerland

After light absorption, a molecule can undergo ra- diationless processes, and photophysics is one of the important general types. The photophysical pro- cesses involve internal conversion （IC） due to elec- tronic nonadiabaticity and intersystem crossing （ISC） induced by spin-orbit coupling. In polyatomic molecules that are excited IC and ISC to vibronic to higher electronic states, levels of lower electronic states are two dominant mechanisms. With the ad- vent of femtosecond ultrashort pulse, tracking and controlling the ultrafast photophysical processes be- come realizable. Due to the fact that ISC requires a change in the spin of an electron, it is usually a slower process than IC. However, extensive reports show that ultrafast competing ISC exists in a number of systems. Re- cently, Richter et al. reported femtosecond ISC in cytosine. Martinez-Fernandez et al. simulated the deactivation dynamics of photo-excited 6-thioguanine using a direct surface hopping dynamics approach Their simulations show that 6-thioguanine is another example of a system showing ultrafast ISC that can compete with IC in the same time scale. Both the spin-orbit and the dynamic couplings are important to describe realistically the excited state dynamics of 6-thioguanine. A similar phenomenon has also been evidenced in the S1 state of benzene. The exper- imental results show that the ultrafast decay of the S1 state is due to competing IC and ISC processes and both processes occur on a femtosecond timescale. Spin-orbit coupling is highly effective when the in- volved states are nearly isoenergetic.

关键词： Ultrafast Imaging electronic relaxation Fragmentation-Ion Spectroscopy

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The evaluation of temporal electronic structures of nonresonant Raman excited virtual state of thiourea

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Chinese Physics B 2011年第4期20卷 280-285页

作者：房超孙立风 Institute of Nuclear and New Energy Technology Tsinghua University Department of Physics Tsinghua University

An algorithm has been introduced to calculate molecular bond polarizabilities of thiourea, which supply essential electronic information about the nonresonant Raman excited virtual states. The main dynamical behaviour of the excited virtual states of thiourea is that the Raman excited electrons tend to flow to the N-H bonds and C-N bonds from the S-C bonds because of the electronic repulsion effect. The difference in Raman excited electron relaxation time of thiourea under 514.5-nm and 325-nm excitations has been observed, which quantitatively shows that the Raman scattering process is dependent on the wavelength of the pumping laser. Finally, the distribution of the electrons at the final stage of relaxation is given out through the comparison between the bond electronic densities of the ground states and the bond polarizabilities after deexcitation.

关键词： Raman intensity electronic relaxation bond polarizability virtual state thiourea

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