SEMIEMPIRICAL MODEL FOR ATOM-ATOM IONIZATION RATES

Numerical calculations are carried out to help interpret ionization rates for rare-gas atoms (particularly argon) obtained in shock-heating experiments. A simplified semiempirical model with three adjustable parameters is used for electronic transitions induced by atom-atom collisions. The three parameters are a measure of the absolute excitation rate from the ground state to the first excited state and of the ratios of different excitation and ionization rates. Numerical results are presented for the total ionization rate as a function of temperature and time for different values of the parameters. Present experiments determine one of the parameters, limit the other two parameters, and yield a relation between them. The possibility for determining all three parameters uniquely from future experiments is discussed.