Electron impact excitation of H2: resonance excitation of B1 u (Jj 2,vj 0) and effective excitation function of EF1 g

The electron impact emission function of the P(3) branch for the (0, 4) band of the H2 B 1? u+?X 1? g+ band system has been measured from threshold to 1800 eV. The emission function exhibits structure indicating strong contributions from both resonance and non-resonance excitation. The non-resonance component contains direct and cascade contributions. A combination of experimental and theoretical considerations permits separation of resonance, dipole-allowed direct, dipole-allowed indirect, and dipole-forbidden excitation components for the Jj = 2, vj = 0 level of the B 1? u+ state. An effective excitation function for the EF 1? g+?X 1? g+ band system has been obtained from a nonlinear least-squares analysis of the dipole-forbidden component of the B 1? u+ state emission function. The absolute value of EF 1? g+?X 1? g+ cross section is established on the basis of earlier experimental results of Liu et al 1995 Astrophys. J. Suppl. 101 375?99 and 2002 Astrophys J. Suppl. 138 229?45 and Abgrall et al 1997 Astrophys. J. 481 557?66 and 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3813?38. A near-threshold apparent resonance excitation cross section of (8.1 ? 3.2) ? 10?18 cm2 is obtained for the B 1? u+ (Jj = 2 and vj = 0). An EF 1? g+?X 1? g+ Born cross section has been calculated from the electronic form factor of Kolos et al 1982a J. Chem. Phys. 77 1335?44. Analysis shows that the Born asymptotic shape function of the EF 1? g+?X 1? g+ band system starts at ~400 eV, a significantly higher energy than previously expected. The excitation function is especially important for interpreting outer planet atmospheric dayglow and auroral activity and can be used to infer energy deposition and heating rates.