Processes Involving Ions and Metastable Atoms in Mercury Afterglows

Abstract

Atomic collision processes occurring in mercury vapor are determined from microwave measurements of the electron density during the afterglow. The electrons are brought into thermal equilibrium with the gas by adding helium to the mercury vapor to act as a "recoil gas." Measurements of the ambipolar diffusion coefficient, $D_a$, of ${\mathrm{Hg}}^{+}$ ions and electrons in helium yield the value $D_{a}n=2.6\mathrm{}\times {10}^{19}$ (${\mathrm{cm}}^2$/sec) (atoms/cc) at 290°K. The corresponding value for ${\mathrm{Hg}}^{+}$ ions in mercury is $D_{a}n=3.6\mathrm{}\times {10}^{17}$ at 350°K. Conversion of the atomic mercury ions to molecular ions according to the reaction ${\mathrm{Hg}}^{+}$+Hg+He→${\mathrm{Hg}}_2^{+}$+He occurs at the rate of 140 ($p_{\mathrm{Hg}}·p_{\mathrm{He}}$) ${\sec }^{-1\mathrm{}}$. The measured recombination coefficient of ${\mathrm{Hg}}_2^{+}$ ions with electrons is $\alpha =5.5\mathrm{}\times {10}^{-7\mathrm{}}$ cc/sec at 400°K. Studies of the ionization produced by the collisions of pairs of mercury metastable atoms yield the values $D_{m}n=1.5\mathrm{}\times {10}^{18}$ (${\mathrm{cm}}^2$/sec) (atoms/cc) for the diffusion coefficient and ${\sigma }_d=8\mathrm{}\times {10}^{-17\mathrm{}}$ ${\mathrm{cm}}^2$ for the de-excitation cross section of ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ metastables at 350°K.