in our previous publication [@li2013], and the chemical physics literature [@lewis_etal2005a; @lewis_etal2005b; @haverd_etal2005; @lewis_etal2008b; @heays2011] with specific discussion of given in @vieitez_etal2008a and @heays2011b.

Electric-dipole-allowed photoabsorption from the ground state occurs for wavelengths shorter than 1000Å and accesses two valence states and several Rydberg series of $^1\Pi_u$ and $^1\Sigma_u^+$ symmetry. Potential-energy curves depicting these states are shown in Fig. \[fig:N2potentials\] with the lowest-energy photoabsorbing state, $b\,{}^1\Pi_u$, occurring at 12.6eV. There is strong electronic coupling between valence and Rydberg states of the same symmetry which leads to a very perturbed spectrum, including constructive and destructive interference in the absorption strength and predissociation rates of vibrational bands [@dressler1969; @spelsberg_meyer2001; @lewis_etal2005a]. Additional rotational interactions between $^1\Pi_u$ and $^1\Sigma_u^+$ states lead to strong rotational dependence of line strengths and predissociation rates (or linewidths) [@stark_etal2005; @heays2011b].

![Diabatic-basis potential-energy curves of N$_2$ excited states relevant to ultraviolet photoabsorption and photodissociation. The energy scale is referenced to $v=0$, $J=0$ of the $X\,{^1\Sigma_g^+}$ ground state and is related to the wavelength scale assuming transitions from this fundamental level. Also indicated are the excitation states of atomic products arising from dissociation and the absorption limit imposed by the ionisation of atomic H. The potential-energy curves of the $c_n{}^1\Pi_u$ and 