Frequency Shifts Due to Hydrogen-Hydrogen Spin-Exchange Collisions

Abstract

The thermal-average cross section $\lambda$ for shifts of the ground-atomic-state hydrogen hyperfine transitions caused by electron spin-exchange collisions between radiating hydrogen atoms has been measured at 308°K by two related techniques using atomic-hydrogen masers. The result is $\lambda =+(4.1\mathrm{}\pm 1.0)\times {10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ and is consistent with calculations relating the hydrogen interaction potentials to the atomic-hydrogen-maser oscillation frequency to within this 70% confidence limit.