Small-angle scattering of metastable hydrogen formed by collisions of neutral hydrogen atoms with gas targets

An experimental investigation has been made of the scattering of metastable hydrogen formed in collisions of neutral hydrogen with helium; projectile energies were in the range 1 to 20 keV and scattering angles investigated range from 0.2° to 1.5°. In addition angular distributions of scattering H${}^0$ and ${\mathrm{H}}^{+}$ were measured in an extended angular range of 0.2° - 5.0°. Total cross sections for $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ formation in helium and argon targets have also been measured. The total cross sections for $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$ formation in helium are in good agreement with coupled-state theoretical predictions at energies above 4.0 keV; the measured differential cross sections show the same angular dependence as theory at 10-keV impact energy. Also, at low energies, a low-angle peak is found in the angular distribution of $\mathrm{H}\mathrm{}\left(2s\right)\mathrm{}$; this is in accordance with theoretical predictions.