Hamburg 2009 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

MO: Fachverband Molekülphysik

MO 13: Molekülphysik Poster 1

MO 13.15: Poster

Dienstag, 3. März 2009, 16:30–19:00, VMP 8 Foyer

Excited-state dynamics of cytosine tautomers — •Kyriaki Kosma, Christian Schroeter, Thomas Schultz, and Ingolf V. Hertel — Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, D-12489 Berlin-Adlershof, Germany

The relaxation dynamics of DNA bases have been extensively studied in the 200-300 nm spectral region [1].

For cytosine, the most stable tautomers in the gas phase are the enol, keto, and keto-imino forms [2], each one absorbing in different regions in the UV [3]. Existing pump-probe experiments study the excited-state lifetime of the enol tautomer with an excitation wavelength of 267 nm [4], while most theoretical studies concentrate on the keto tautomer, the second most stable form [5, 6].

We disentangled the different relaxation dynamics of the cytosine tautomers, by exciting the molecules in a cold molecular beam with five different wavelengths in the range 260-290 nm. Different lifetimes were observed and assigned to two of the tautomers, i.e. the enol and keto forms. A long lifetime of >200 ps was observed for the first time and assignment to the triplet state of keto-cytosine is proposed.

[1] Carlos E. et al., Chem. Rev. 2004, 104, 1977

[2] Tomic K. et al., J. Phys. Chem. A 2005, 109, 8410

[3] Nir E. et al., Chem. Phys. Lett. 2002, 355, 59

[4] Kang H. et al, J. Am. Chem. Soc. 2002, 124, 12958

[5] Ismail N. et al., J. Am. Chem. Soc. 2002, 124, 6818

[6] Zgierski M. Z. et al., Chem. Phys. Lett. 2008, 463, 289