Mobility of Mercury Ions in Mercury Vapor

Measurements of mercury ion drift velocities and mobilities in mercury vapor by the Hornbeck technique have been made over a range of electric-field strength divided by reduced pressure ($\frac{E}{p_0}$) from 40 to 1500 V / (cm×mm Hg). Two stable mercury ions, believed to be ${\mathrm{Hg}}^{+}$ and $\mathrm{Hg}_2^{}{}_{}{}^{+}$, have been observed. The zero-field mobility of the two ions found by a long extrapolation gives the atomic ion ${\mathrm{Hg}}^{+}$ a zero-field mobility of 0.24±0.03 ${\mathrm{cm}}^2$/V-sec while the molecular ion mobility is estimated at 0.45±0.05 ${\mathrm{cm}}^2$/V-sec. The atomic ion value is in good agreement with theory; the molecular ion value is appreciably lower than the theoretical prediction. Charge exchange cross sections for ${\mathrm{Hg}}^{+}$ in Hg computed from present data are higher by a factor of nearly 1.5 than values measured directly but are qualitatively in line with rare-gas values measured by the present method. The secondary electron emission coefficient from a surface due to positive ion bombardment ${\gamma }_i$ has been calculated for the two cathodes used: ${\gamma }_i$ for molybdenum is estimated by 5×${10}^{-5\mathrm{}}$ electron per positive ion striking the cathode surface; ${\gamma }_i$ for an oxide-coated nickel surface is estimated at 2×${10}^{-2\mathrm{}}$ electron per positive ion striking the cathode.