Photoelectron-recoil-induced rotational excitation of the $B{}^2\Sigma _u^{+}$ state in $\mathrm{N}_2{}^{+}$

In the photoelectron spectrum of ${\mathrm{N}}_2$ the apparent ionization energy to form the $B{}^2\Sigma _u^{+}$ state increases linearly with the photon energy. Rotationally resolved measurements of the fluorescent decay of this state show a linear increase of rotational heating with increasing photon energy. These results are in quantitative agreement with the prediction of the theory of recoil-induced rotational excitation, indicating that the rotational heating that has been observed previously arises primarily from such recoil-induced excitation. Together with other results that have been reported they show that recoil-induced internal excitation is significant in many situations, including near threshold.

Figure 1

Mean apparent ionization energy to produce the $v=0$ $B$ state of $\mathrm{N}_2{}^{+}$ as a function of photoelectron kinetic energy. Solid circles, left-hand axis: From photoelectron spectroscopy. Squares and triangles, right-hand axis: From fluorescence measurements. Triangles are from this work and squares are from Ref. 7. The solid line represents a least-squares fit of a straight line to the photoelectron data. The dotted line shows the predictions of a quantum-mechanical theoretical model.