We investigated dissociation of X-(H2O)(n) (X=Cl, I, n=13-31) by the impact onto a (La0.7Ce0.3)B-6(100) surface at a collision energy E-col of 1-5 eV per water molecule in a tandem time-of-flight mass spectrometer equipped with a translation-energy analyzer. The mechanism of the dissociation was elucidated on the basis of the measurements of the mass spectrum and the translational energies of the product anions, X-(H2O)(m) (m=0-4), scattered from the surface. It was concluded that (1) the parent cluster anion impacted on the surface undergoes dissociation on the surface under quasiequilibrium with its characteristic time varying with E-col and n, and (2) the total collision energy introduced is partitioned preferentially to the translational motions of the products on the surface and to the rotational, the vibrational, and the lattice vibrational motions (surface) in this order. The quasiequilibrium model is applicable, even at the collision energy as low as 1 eV, because the translational modes are found to be statistically distributed while the other modes are not much populated by dynamical and energetics limitation. (C) 2004 American Institute of Physics.