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

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.