Energy redistribution in cluster–surface collision: I2− (CO2)<i>n</i> onto silicon surface

Abstract

Fragmentation of I2−(CO2)n (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 ∼10−8 Pa. At the collision energy (per I2−) of 50 eV and the incident angle of 26° 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, Ts∥ 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 Ts∥ (6000–12 000 K) with n is interpreted as an increasing extent of cluster–impact heating with n, while the reduction of Ts∥ in the 13≤n≤∼19 range is attributable to efficient transmission of the I− and I2− translational energies to the CO2 solvent cage. The effective volume and pressure of I2−(CO2)n colliding on the surface were estimated; at n=10, the volume and the pressure were 100 nm3 and 10 MPa, respectively.