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~10⁶ cm/sec). The cross sections were determined by measuring the attenuation of a beam of H(2S) 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 H(2S) velocity ≈1×10⁶ cm/sec, the measured cross sections are σ(helium)=81±12 ²/atom, σ(neon)=80±12 ²/atom, σ(argon)=91±14 ²/atom, and σ(krypton)=108±16 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.