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Author: Fingerhut, Benjamin P. × End date: 2024 × Start date: 2020 × DDC: 500 × Type: article × Publisher: Melville, NY : AIP Publishing LLC ×

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    Molecular couplings and energy exchange between DNA and water mapped by femtosecond infrared spectroscopy of backbone vibrations
    (Melville, NY : AIP Publishing LLC, 2017) Liu, Yingliang; Guchhait, Biswajit; Siebert, Torsten; Fingerhut, Benjamin P.; Elsaesser, Thomas
    Molecular couplings between DNA and water together with the accompanying processes of energy exchange are mapped via the ultrafast response of DNA backbone vibrations after OH stretch excitation of the water shell. Native salmon testes DNA is studied in femtosecond pump-probe experiments under conditions of full hydration and at a reduced hydration level with two water layers around the double helix. Independent of their local hydration patterns, all backbone vibrations in the frequency range from 940 to 1120 cm-1 display a quasi-instantaneous reshaping of the spectral envelopes of their fundamental absorption bands upon excitation of the water shell. The subsequent reshaping kinetics encompass a one-picosecond component, reflecting the formation of a hot ground state of the water shell, and a slower contribution on a time scale of tens of picoseconds. Such results are benchmarked by measurements with resonant excitation of the backbone modes, resulting in distinctly different absorption changes. We assign the fast changes of DNA absorption after OH stretch excitation to structural changes in the water shell which couple to DNA through the local electric fields. The second slower process is attributed to a flow of excess energy from the water shell into DNA, establishing a common heated ground state in the molecular ensemble. This interpretation is supported by theoretical calculations of the electric fields exerted by the water shell at different temperatures.
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    Monitoring conical intersections in the ring opening of furan by attosecond stimulated X-ray Raman spectroscopy
    (Melville, NY : AIP Publishing LLC, 2015) Hua, Weijie; Oesterling, Sven; Biggs, Jason D.; Zhang, Yu; Ando, Hideo; de Vivie-Riedle, Regina; Fingerhut, Benjamin P.; Mukamel, Shaul
    Attosecond X-ray pulses are short enough to capture snapshots of molecules undergoing nonadiabatic electron and nuclear dynamics at conical intersections (CoIns). We show that a stimulated Raman probe induced by a combination of an attosecond and a femtosecond pulse has a unique temporal and spectral resolution for probing the nonadiabatic dynamics and detecting the ultrafast (∼4.5 fs) passage through a CoIn. This is demonstrated by a multiconfigurational self-consistent-field study of the dynamics and spectroscopy of the furan ring-opening reaction. Trajectories generated by surface hopping simulations were used to predict Attosecond Stimulated X-ray Raman Spectroscopy signals at reactant and product structures as well as representative snapshots along the conical intersection seam. The signals are highly sensitive to the changes in nonadiabatically coupled electronic structure and geometry.