Energy Analysis and Model Calculations of Collisional Acceleration in Seeded Molecular Beams. Application to Xe/He and C60/He

Abstract

A simple theoretical model for the aerodynamic acceleration of heavy particles in seeded molecular beams in the hyperthermal energy range 1−60 eV is presented. The model gives a microscopically detailed picture of the collisional acceleration dynamics in terms of the number of collisions at a given distance downstream from the nozzle aperture. The basic model applies to an ideal isentropic free jet center line expansion with hard spheres collisions but is also modified to include capillary nozzle effects. The model predictions are compared with experimental measurements of terminal kinetic energies of Xe accelerated in He in the constant flux mode up to 11.5 eV and C60 accelerated in He in the constant flux mode up to 56 eV and in the constant temperature mode up to 41 eV. Good agreement between calculation and experiment is obtained. The applicability of the hard sphere approximation for describing the acceleration dynamics of superhot C60 in He shows that C60 can be treated here as a “quasi-atom” and th...