ELECTRON-IMPACT EXCITATION AND EMISSION CROSS-SECTIONS OF THE H-2 LYMAN AND WERNER SYSTEMS

Excitation functions of the H-2 Lyman (Ly) (B (1)Sigma(u)(+) - X (1)Si gma(g)(+)) and Werner (W) (C (1)Pi(u) - X (1)Sigma(g)(+)) band systems have been reanalyzed using a combination of measurements and theoreti cal considerations. These systems are prominent emitters in outer plan et atmospheric dayglow and auroral activity and can be used to infer e nergy deposition and heating rates. Earlier measurements of the cross sections reported by Shemansky et al. [1985a] have been found to be in accurate in the threshold energy region. A combination of high-resolut ion spectral and shape function measurements obtained at the Jet Propu lsion Laboratory (JPL) in low- and medium-energy regions have been use d to obtain relative excitation shape functions of the two systems. At energies above 250 eV, we have used the measurements obtained earlier by De Heer and Carriere [1971] in order to define the first two terms of the Born electric dipole collision strength. The complete set of c ollision strength terms is obtained by combining: the: JPL and De Heer and Carriere [1971] data. We have found that, contrary to results of, Shemansky et al. [1985a], the shape functions of the Ha Ly and W syste ms, expressed in units of threshold energy, are the same: within exper imental error. Absolute cross sections of the Ha Ly and W systems are established using the theoretical oscillator strengths of Abgrall et a l. [1987, 1993a, b, c] and Abgrall and Roueff [1989]. The atomic hydro gen H-2 Ly a emission cross section resulting fi om dissociative excit ation of Ha at 100 eV obtained from relative! intensities of H2 W emis sion lines is also derived and compared with other experimental measur ements. At a gas temperature of 300 K and electron energy of 100 eV, t he cross sections for the H Ly alpha, H-2 Ly, and W emissions are (0.7 16 +/- 0.095) x 10(-17), (2.62 +/- 0.34) x 10-17, and (2.41 +/- 0.31) x 10-17 cm(2), respectively. The accuracy of the absolute values and s hape functions is limited primarily by electron gun performance, as wa s the case for Shemansky et al. The rotational dependence of the, tran sition dipole matrix elements and perturbations between the B (1)Sigma (u)(+) and C (1)Pi(u)(+) states have a significant effect on the cross sections.