Elastic electron scattering cross sections for molecular hydrogen

Using an electron-beam–molecular-beam apparatus and employing the relative flow technique, ratios of the differential elastic scattering cross sections (DCS’s) of ${\mathrm{H}}_2$ to He were measured at incident electron energies of 15–100 eV and angular range of 10°–125°. From these ratios, the absolute elastic DCS’s for ${\mathrm{H}}_2$ were determined by normalization to accurate, available elastic DCS’s of He. Since pure rotational structure was not resolved in this work, the DCS’s reported are the sum of elastic and rotational excitations of ${\mathrm{H}}_2$ at room temperature. The reliability of the relative flow normalization to He was checked at each energy and angle by performing similar elastic DCS measurements on Ne (for which the cross sections are known). The resulting absolute Ne DCS’s were found to be in good agreement (within 10%) with the Ne elastic DCS’s measured previously [D. F. Register and S. Trajmar, Phys. Rev. A 29, 1785 (1984)]. From the DCS’s, integral and momentum-transfer cross sections were calculated. The present results are compared with other recent measurements.