Back flux at polyatomic gas expansion for pulsed laser evaporation

The back flux value at polyatomic gas expansion under pulsed laser evaporation is determined on the basis of one-dimensional direct Monte Carlo simulation. Calculations are performed for a wide range of evaporated matter amount. Taking into account rotational and vibrational degrees of freedom substantially increases the back flux. Dependence of the back recondensed fraction on the relaxation collision number is shown. The data are generally in good agreement with available analytical predictions. Importance of consideration of energy transfer from the internal degrees of freedom to the translational ones is illustrated by an example of pulsed laser evaporation of polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA).