  Pronounced maximum absorption of laser light irradiating a rare-gas or metal
cluster is widely expected during the linear resonance (LR) when Mie-plasma
wavelength $\lambdaM$ of electrons equals the laser wavelength $\lambda$. On
the contrary, by performing molecular dynamics (MD) simulations of an argon
cluster irradiated by short 5-fs (fwhm) laser pulses it is revealed that, for a
given laser pulse energy and a cluster, at each peak intensity there exists a
$\lambda$ -- shifted from the expected $\lambdaM$ -- that corresponds to a {\em
unified dynamical} LR at which evolution of the cluster happens through very
effective unification of possible resonances in various stages, including (i)
the LR in the initial time of plasma creation, (ii) the LR in the Coulomb
expanding phase in the later time and (iii) anharmonic resonance in the
marginally over-dense regime for a relatively longer pulse duration, leading to
maximum laser absorption accompanied by maximum removal of electrons from
cluster and also maximum allowed average charge states for the argon cluster.
Increasing the laser intensity, the absorption maxima is found to shift to a
higher wavelength in the band of $\lambda\approx (1-1.5)\lambdaM$ than
permanently staying at the expected $\lambdaM$. A naive rigid sphere model also
corroborates the wavelength shift of the absorption peak as found in MD and
un-equivocally proves that maximum laser absorption in a cluster happens at a
shifted $\lambda$ in the marginally over-dense regime of $\lambda\approx
(1-1.5)\lambdaM$ in stead of $\lambdaM$ of LR. Present study may find
importance for guiding an optimal condition laser-cluster interaction
experiment in the short pulse regime.
