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Vibrational Energy Dependence of the Triplet Lifetime in Isolated, Photo-Excited C60

Journal article
Authors O. Echt
S. Yao
R. Deng
Klavs Hansen
Published in J. Phys. Chem. A
Volume 108
Pages 6944-6952
ISSN 1089-5639
Publication year 2004
Published at Department of Physics (GU)
Pages 6944-6952
Language en
Links dx.doi.org/10.1021/jp048313u
Subject categories Physical Sciences, Atom and Molecular Physics and Optics

Abstract

We have measured the lifetime of the lowest triplet state T1 in free C60 by a pump-probe experiment using lasers with nanosecond pulse durations. At low pump fluence the population of T1 decays with a distinct, narrow distribution of lifetimes. depends on the pump wavelength ( = 532, 355, or 266 nm) as well as the temperature of the source from which C60 is vaporized (420 T 510 C); it ranges from 2 s to 0.3 s. At high pump fluence an additional lifetime as short as 40 ns is observed. A consistent correlation of all observed lifetimes with the experimental parameters is found if is assigned to an ensemble of C60 (T1) that has absorbed either one or two pump photons with the excess energy being randomized over all vibrational modes. Thus, = 2 s corresponds to a vibrational energy Evib = Etotal - Etriplet = 4.6 eV (one-photon absorption at = 532 nm, T = 420 C) while = 40 ns corresponds to Evib = 9.6 eV (two-photon absorption at 355 nm, 480 C). This result strongly suggests that delayed electrons that are emitted from highly excited C60 (Evib 10 eV) on the time scale of 10 ns to 1 ms are not affected by long-lived electronically excited states. The frequently questioned description of delayed electron emission from photoexcited C60 as thermionic emission is, therefore, warranted.

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