For the energy absorption of atomic clusters as a function of the laser pulseduration we find a similar behavior as it has been observed for metallicclusters [K\"oller et al., Phys. Rev. Lett. {\bf 82}, 3783 (1999)]. In bothsituations there exists an optimum radius $R_{o}$ of the cluster for energyabsorption. In the metallic case the existence of $R_{o}$ has been interpretedas a consequence of the collective oscillation of a delocalized electron cloudin resonance with the laser frequency. Here, we give evidence that in theatomic cluster the origin of $R_{o}$ is very different. Based on field assistedtunneling it can be related to the phenomenon of enhanced ionization as itoccurs in small molecules. The dependence of $R_{o}$ on the laser frequencyturns out to be the key quantity to distinguish the processes.
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