Excitation of the E,F1Σ+/sub 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+/sub g/ and the H1Σ+/sub g/ electronic states of neutral H2. The E1Σ+/sub g/→B1Σ+/sub u/, F1Σ+/sub g/→B1Σ+/sub u/, and H1Σ+/sub g/ →B1Σ+/sub u/ band systems are observed at an effective spectral slit width of < or =2 A, 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 lambda=4686 A (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) x 10-18 cm2 as a lower-limit estimate of the E1Σ+/sub g/ direct cross section at 200 eV