Excitation of the Werner Bands of H2 by Electron Impact

Abstract

Absolute cross sections for the excitation of the Werner band system ${\mathrm{H}}_2{\mathrm{(C\hspace{0.17em}}}^1{\Pi }_u{\mathrm{\to \; X\hspace{0.17em}}}^1{\Sigma }_g^{+})$ have been measured from energy threshold to 300 eV for electron impact on H₂. The bands were observed in emission in the wavelength region 1100–1250 Å. The measured cross sections were compared with published transition probabilities, leading to the conclusion that the Werner bands are suitable as the basis for a relative spectral response calibration only when the bands are observed under sufficiently high resolution ($\mathrm{FWHM}\text{∼0.4}$ Å). The effect of the perturbation between the C ¹Π_u and ${\mathrm{B\hspace{0.17em}}}^1{\Sigma }_u^{+}$ states of the hydrogen molecule was clearly observed in anomalies in the rotational intensity distribution in bands of the $\text{(3,\hspace{0.17em}v″)}$ progression.