Figure 1

Potential energy diagram for ${\text{N}}_2$ and ${\text{N}}_2{}^{+}$ showing from top down at the right: $C$ ${}^2{\Sigma }_u^{+}$ [6]; the Rydberg series $R$($C$) $n=4$ [7]; $R$($C$) $n=3$; NRDER 2 that predissociates the $R$($C$) $n=4$ and $n=5$ states to produce ${\text{N}}^{*}$ 4$P$ states; $D$ ${}^2{\Pi }_g^{+}$ [8]; NRDER 1 which is directly excited and promptly dissociates to produce ${\text{N}}^{*}$ 4$P$ states; the Rydberg series $R$($D$) $n=4$ state [9]. The arrow at the right indicates the production threshold for ${\text{N}}^{*}$ 4$P$ states, and the two arrows at the left indicate the energies of the intensity feature maxima at $21.6$ and 23 eV (see text). The NRDER and R(x) curves are based on the analyses of Refs. [7, 9, 10] and on quantitative considerations discussed below. The dashed gray vertical lines show the center and bounds of the Franck-Condon region [11].Reuse & Permissions

Figure 2

Apparatus schematic showing (1) incident photon beam from ALS synchrotron, linearly polarized in the plane of the diagram, (2) insertable four-reflection quarter-wave retarder, (3) beam-defining aperture, (4) effusive ${\text{N}}_2$ target, (5) optical polarimeter at the magic angle, (6) photon-counting photomultiplier tube, (7) photodiode for incident photon flux normalization, and (8) linear photon polarimeter.Reuse & Permissions

Figure 3

(a) 818-nm intensity data: The solid black line is the present intensity data, and the open circles are the experimental results of Erman et al. [9]. The position of the vibrational structure is based on the assignments of Codling [7]. (b) The solid circles are the present circular polarization $P_3$ data.Reuse & Permissions

Figure 4

Configurations of various neutral ${\text{N}}_2$ molecular states including the ground state ($X$), Rydberg states converging to the ions ${\text{N}}_2{}^{+}$ $C$ [$R\left(C\right)$] and $D$ [$R\left(D\right)$], and NRDER states discussed in various references (see text). The $G$ $1{\sigma }_{g}1{\sigma }_u$ orbitals are filled for all of these states and are not shown. In the cases where two configurations have been suggested for a given state [$R\left(D\right)$ [30] and the NRDER proposed by Wendin [12, 29]] both are shown, with the primary configuration at the left.Reuse & Permissions