Electron-impact excitation of the D /sup 3/. sigma. /sub u//sup +/ and c/sub 4//sup prime/ /sup 1/. sigma. /sub u//sup +/ Rydberg states of N/sub 2/

Absolute optical-emission excitation functions have been measured for the $D ^{3}\ensuremath{\Sigma}_{u}^{+}\ensuremath{\rightarrow}B ^{3}\ensuremath{\Pi}_{g}$ fourth positive system bands ($0,{v}^{\ensuremath{'}\ensuremath{'}}$) with ${v}^{\ensuremath{'}\ensuremath{'}}=0,1,2,3,4,5,6$ and for the ${c}_{4}^{\ensuremath{'}} ^{1}\ensuremath{\Sigma}_{u}^{+}\ensuremath{\rightarrow}a ^{1}\ensuremath{\Pi}_{g}$ Gaydon-Herman singlet system bands ($0,{v}^{\ensuremath{'}\ensuremath{'}}$) with ${v}^{\ensuremath{'}\ensuremath{'}}=0,1,2,3,4,5$ produced by electron-impact excitation of the ${\mathrm{N}}_{2} X^{1}\ensuremath{\Sigma}_{g}^{+}(v=0)$ ground state, for incident electron energies ranging from threshold to 440 eV. We find that the $D\ensuremath{\rightarrow}B$ emission has a principal maximum at 14.1\ifmmode\pm\else\textpm\fi{}0.3 eV, a smaller maximum (83% of principal maximum) at 23 eV, and an ${E}^{\ensuremath{-}3}$ energy dependence for incident electron energies $Eg65$ eV. Measurements over the energy range 13.5-31 eV indicate the $D\ensuremath{\rightarrow}B$ emission is unpolarized. The sum over ${v}^{\ensuremath{'}\ensuremath{'}}$ of the $D\ensuremath{\rightarrow}B (0,{v}^{\ensuremath{'}\ensuremath{'}})$ optical-emission cross sections gives a maximum value 1.27 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}19}$ ${\mathrm{cm}}^{2}$ for the apparent cross section for the $v=0$ vibrational level of the $D ^{3}\ensuremath{\Sigma}_{u}^{+}$ state excited by electron collision with the ${\mathrm{N}}_{2} X ^{1}\ensuremath{\Sigma}_{g}^{+}(v=0)$ ground state. The appearance of two maxima in the $D\ensuremath{\rightarrow}B$ optical emission is qualitatively confirmed by other experimental work. This point is discussed. For the ${c}_{4}^{\ensuremath{'}}\ensuremath{\rightarrow}a$ emission we find a single very broad maximum near 80 eV and for $Eg110$ eV an energy dependence described by the form $(\frac{{C}_{1}}{E})\mathrm{ln}(\frac{E}{{C}_{2}})$. The ${c}_{4}^{\ensuremath{'}}\ensuremath{\rightarrow}a$ optical-emission cross sections were obtained by extrapolating measurements to low pressure (0.1 mTorr) in order to account for the nonlinear pressure dependence of the ${c}_{4}^{\ensuremath{'}}\ensuremath{\rightarrow}a$ emission caused by absorption of the very intense ${c}_{4}^{\ensuremath{'}}\ensuremath{\rightarrow}X (0,0)$ band radiation. The sum over ${v}^{\ensuremath{'}\ensuremath{'}}$ of our measured optical-emission cross sections for the ${c}_{4}^{\ensuremath{'}}\ensuremath{\rightarrow}a (0,{v}^{\ensuremath{'}\ensuremath{'}})$ bands has a maximum value 1.0 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}19}$ ${\mathrm{cm}}^{2}$. This result, when combined with the absolute ${c}_{4}^{\ensuremath{'}}\ensuremath{\rightarrow}X (0,0)$ band-emission cross section of Zipf and McLaughlin and the ${c}_{4}^{\ensuremath{'}}\ensuremath{\rightarrow}X (0,1)$ cross section of Aarts and DeHeer, yields an upper bound of 0.006 for the ${c}_{4}^{\ensuremath{'}}(0)\ensuremath{\rightarrow}a$ optical branching ratio, i.e., more than 99.4% of ${c}_{4}^{\ensuremath{'}} ^{1}\ensuremath{\Sigma}_{u}^{+}(v=0)$ molecules will decay to the ground state.