Elastic scattering of intermediate energy electrons by HCN

Abstract
Utilizing a crossed electron beam–molecular beam geometry and a relative gas flow technique, ratios σ (HCN,ϑ)/σ (He,ϑ) of elastic differential cross sections of HCN to those of He have been measured at electron impact energies of 3,5,11.6, 21.6, and 50 eV and at scattering angles of 20° to 130°. Normalized absolute values of σ (HCN,ϑ) have been obtained by multiplying these ratios by the absolute values of σ (He,ϑ) reported previously. Since the rotational–vibrational structure in HCN was not resolved in the present measurements, the term elastic here includes contributions from elastic scattering, as well as from pure rotational and the 1–0, ν2 vibrational excitations. The elastic differential cross sections have been compared with the predictions of the Born approximation and classical perturbation theory. For angular regions lying between 0° and 20°, and 130° and 180°, σ (HCN,ϑ) values have been obtained by extrapolation. These values have been used to calculate the integral and momentum-transfer cross sections.

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