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A: Fachverband Atomphysik
A 8: Atomic Clusters I
A 8.6: Talk
Tuesday, March 3, 2009, 12:15–12:30, VMP 6 HS-B
The temperature dependence of the lifetime of the first excited electronic state in C60 anions studied using two color pump-probe photoelectron spectroscopy — •Mattias Svanqvist, Raphael Kuhnen, and Bernd von Issendorff — University of Freiburg
The electronic valence structure of fullerenes is determined by the delocalized π-band which can be seen as a spherical two-dimensional electron gas. This makes fullerenes interesting model systems for the study of excitation and relaxation processes in a highly correlated many electron systems.
We have studied the temperature and pump beam intensity dependence on the lifetime of the first excited state (t1g) in C60 anions in a molecular beam. The lifetime of this state has previously been reported as 2.2 ± 0.2[1]. We show that the measured lifetime is dependent on the temperature of the fullerenes and the intensity of the pump laser.
We have used a pump beam wavelength of 800 nm and two different probe beam wavelengths: 400 nm and 266 nm. The 1.55 eV absorbed by the molecule is clearly more than the observed energy gap between the t1u and t1g, which has a value of around 1.1 eV. We assume that the energy difference goes into vibrations thus heating the molecule, which means that the observed lifetime of the t1g level also should depend on the pumping beam wavelength.
We conclude that the interpretation of lifetime measurements of excited states in non-adiabatic systems needs to take into consideration at least two parameters: initial temperature and pump beam heating.