Studies of the Mechanism of Electron-Ion Recombination. I

Microwave and optical techniques are used to study the loss of electrons during the afterglow following microwave discharges in noble gases, principally in neon and argon. The time and pressure dependences of the electron density decays follow a two-body volume electron-ion recombination law over a wide range of variables, yielding recombination coefficients in the range ${10}^{-7\mathrm{}}$-${10}^{-6\mathrm{}}$ cc/sec for neon and for argon. The after-glow radiation is shown to originate in the volume of the ionized gas, far from the walls, and to decrease in intensity when the electron energy is momentarily increased. Both of these observations are consistent with volume recombination loss of electrons leading to the formation of excited atoms. Further, the intensity of the afterglow radiation is observed to vary in time in the same manner as the square of the electron density, and absolute intensity determinations in neon and in argon yield recombination coefficients consistent with the values obtained from the electron-density decay curves. As a test of the hypothesis that dissociative recombination, $X_2^{}{}_{}{}^{+}+e\to X^{*}+X$, is responsible for the large recombination loss observed in microwave afterglows, measurements are made under conditions first where only ${\mathrm{Ar}}^{+}$ ions and then where only $\mathrm{Ar}_2^{}{}_{}{}^{+}$ ions are expected in the afterglow. The usual large recombination loss of electrons is observed when $\mathrm{Ar}_2^{}{}_{}{}^{+}$ ions are present, but at the same charge densities, only ambipolar diffusion loss of electrons and ${\mathrm{Ar}}^{+}$ ions is observed.