Plasma density effects on the three-body recombination rate coefficients

The existing reaction rate coefficients for the three-body recombination of ions with plasma electrons have a strong T-4.5 dependence on the electron temperature T, which seems to break down at low temperature, for T < 1 K similar or equal to 10(-4) eV. The obvious deficiency of the formula is the neglect of the plasma density effect on the recombined Rydberg states. A simple correctional procedure is adopted in terms of a density dependent cutoff of these high Rydberg states, which seems to improve the rates at low T. The total rate coefficients are now proportional to T-1, for the density N not too low. The T dependence is closely related to the density, so that the -4.5 exponent is still valid at high T and low N region. Some numerical examples are given, and possible further improvements are suggested. The high and low T formulas interpolate smoothly through the principal quantum number cutoffs. (C) 1997 Published by Elsevier Science B.V.