Excitation of the E,F1Σ+g states of H2 by electron impact

Abstract

Optical excitation functions produced by low‐energy electron impact excitation are reported for several rotational lines originating from the E,F¹Σ⁺_g and the H¹Σ⁺_g electronic states of neutral H₂. The E¹Σ⁺_g→B¹Σ⁺_u, F¹Σ⁺_g→B¹Σ⁺_u, and H¹Σ⁺_g →B¹Σ⁺_u band systems are observed at an effective spectral slit width of ?2 Å, over an electron energy range 0–300 eV. The observed transitions are identified as originating from v′=2,3,4 vibrational levels of the E state, the v′=5 level of the F state, and the v′=2 level of the H state. Absolute emission cross section measurements are obtained at 200 eV electron energy and 30 mtorr H₂ gas pressure through direct comparison with the λ=4686 Å (n=4→3) line of the He II spectrum. Analysis of the E→B (2,1) R0 rotational line intensity yields (1.0±0.3) ×10⁻¹⁸ cm² as a lower‐limit estimate of the E¹Σ⁺_g direct cross section at 200 eV.