400$. The dominant reservoir of elemental N is in the form of atoms and N$_2$, which are essentially unobservable outside of the solar system, the former because its ionic form, N$^+$, is readily removed by charge exchange with neutral hydrogen with the latter lacking a rotational emission spectrum because it is homonuclear. The observation of electronic transitions of N$_2$ is limited to technically-challenging ultraviolet (UV) wavelengths shorter than 1000Å.

There have been numerous detections of N-derived molecules such as , $\mathrm{CN}$, $\mathrm{HCN}$, and in interstellar space, protostellar envelopes and discs, and extra-galactically, [e.g., @van_zadelhoff2001; @bergin2002; @gerin2009; @oberg2010; @tobin2012], as well as for their isotopologues [e.g., @wannier1991; @gerin2009; @adande2012; @hily-blant2013; @bizzocchi2013; @daniel2013]. The balance of chemically active N and highly stable N$_2$ is an important parameter in the chemistry of these more complex amines and nitriles. The primary driver of this balance in environments exposed to an ultraviolet flux is photodissociation of N$_2$.

The value of $\mathrm{{}^{14}N}/\mathrm{^{15}N}$ in observable species constitutes an astronomical puzzle. The solar elemental ratio, 440 [@marty2010], is considered representative of the local interstellar medium, but differs from the terrestrial value, 270; in the atmospheric of Titan, 180 [@niemann_etal2005]; and in interplanetary dust, meteorites and comets, [68–330 [@floss2006; 