Temperature dependence of the hydrogen-hydrogen spin-exchange cross section

Spin-exchange relaxation rates are measured, as a function of the atomic hydrogen density, in the storage bulb of a hydrogen maser of special design. The values of the hydrogen-hydrogen spin-exchange cross section in the temperature range 77-363 K result. These experimental values are in very good agreement with the result of a theoretical calculation by Allison. For ambient temperature, the experimental value is $\sigma =23.1\mathrm{}\pm 2.8$ ${\mathrm{\AA }}^2$ (the theoretical value is 23.5 ± 2.4 ${\mathrm{\AA }}^2$) and it varies slowly with temperature.