Collisional Quenching of Metastable Hydrogen

Measurements of the collisional quenching of the $2S$ state of atomic hydrogen by helium, neon, argon, and krypton have been made. The energy range was in the thermal region ($v\sim {10}^6$ cm/sec). The cross sections were determined by measuring the attenuation of a beam of $\mathrm{H}\mathrm{}\left(2S\right)\mathrm{}$ atoms in passing through targets of the various gases. Time-of-flight techniques were used to measure the velocity dependences of the cross sections. For an incident $\mathrm{H}\mathrm{}\left(2S\right)\mathrm{}$ velocity $\approx 1\times {10}^6$ cm/sec, the measured cross sections are $\sigma \left(\mathrm{helium}\right)=81\mathrm{}\pm 12$ ${\mathrm{\AA }}^2$/atom, $\sigma \left(\mathrm{neon}\right)=80\mathrm{}\pm 12$ ${\mathrm{\AA }}^2$/atom, $\sigma \left(\mathrm{argon}\right)=91\mathrm{}\pm 14$ ${\mathrm{\AA }}^2$/atom, and $\sigma \left(\mathrm{krypton}\right)=108\mathrm{}\pm 16$ ${\mathrm{\AA }}^2$/atom. The results for helium are 10-15% higher than theoretical results obtained by Slocomb, Miller, and Schaefer and 20-25% higher than a calculation by Byron and Gersten using a pseudopotential method.