Berlin 2014 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 5: Posters 1: Electronic Spectroscopy, Photochemistry, Femtosecond Spectroscopy

MO 5.25: Poster

Montag, 17. März 2014, 16:30–18:30, Spree-Palais

Excited state of guanosine in water - a time-resolved photoelectron study — •Franziska Buchner and Andrea Lübcke — Max-Born-Institute Berlin, Germany

Interaction of ultraviolet light with DNA molecules may lead to photodamage and consequently may cause development of cancer. Upon excitation, natural DNA bases reveal ultrafast relaxation mechanisms that prevent photodamage.

We studied the time-resolved photoelectron spectrum of guanosine (the nucleoside of the DNA base guanine) in liquid water. Sub-100 fs pulses of 266 nm or 238-248 nm excite an 1 mmolar buffered solution of guanosine. The relaxation of the resonantly excited state is probed by photoionization using delayed ultrashort UV pulses of different photon energies. The kinetic energy distribution of the photoelectrons resembles the time-dependent binding energy of the excited state. Due to the broad absorption band of guanosine, also the probe pulse induces dynamics (negative temporal direction). From the comparison of the results for different pump wavelength, we can derive information about the role of higher lying excited states.

Additional information is derived from the one-colour multi-photon ionization, when only the pump or the probe pulse is present. We will describe and interpret in detail the photoelectron spectra in terms of the excited state dynamics of guanosine.