Fragmentation of I-2(-) (CO2), (n = 1-30) by its collision on a silicon surface was investigated by measuring the fragment anions and their translational energy parallel to the surface (surface-parallel translational energy) in a tandem time-of-flight mass spectrometer equipped with a collision chamber evacuated down to similar to 10(-8) Pa. At the collision energy (per I-2(-)) of 50 eV and the incident angle of 26 degrees with respect to the surface normal, the distributions of the surface-parallel translational energies of the fragment anions from a given parent cluster anion were found to obey the one-dimensional Maxwell-Boltzmann distribution with the same translational temperature, T-s(parallel to). The results show that the cluster anion and its neighboring surface atoms reach quasiequilibrium before the fragment anions leave the surface. A general increasing trend of T-s(parallel to) (6000-12 000 K) with n is interpreted as an increasing extent of cluster-impact heating with n, while the reduction of T-s(parallel to) in the 13 less than or equal to n less than or equal to similar to 19 range is attributable to efficient transmission of the I- and I-2(-) translational energies to the CO2 solventcage. The effective volume and pressure of I-2(-) (CO2), colliding on the surface were estimated; at n = 10, the volume and the pressure were 100 nm(3) and 10 MPa, respectively.