[$\mathrm{SiV}^{0}$]{}, allowing both present charge states to be quantified simultaneously and reliably. We note that even with the present uncertainty, our results remain incompatible with the value derived from first-principles calculations [@Kern2017].

The silicon-vacancy-nitrogen defect {#sec:sivn}
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Defect identification
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EPR measurements of samples D–F reveal a previously-unidentified multi-line ${S=1/2}$ spectrum at approximately $g=\num{2.004}$. Initial analysis indicated a defect which possessed a ${I=1/2}$ nucleus with a small hyperfine interaction. As these samples are [$^{15}\mathrm{N}$]{}-enriched, the nucleus involved could either be or . An additional sample, [Sample G]{}, which was grown under similar conditions to Samples A–F but with natural abundance nitrogen rather than [$^{15}\mathrm{N}$]{}-enriched gasses and subsequently annealed at for , was studied to identify the nucleus involved. We again observe a previously-unidentified multi-line ${S=1/2}$ spectrum at approximately $g=\num{2.004}$, with more transitions than in the -doped samples \[Fig \[fig:110\_and\_roadmap\](a)\]. In conjunction with the angular variation of the spectrum \[Fig \[fig:110\_and\_roadmap\](b)\], the spectrum was identified as belonging to a defect possessing a nuclear spin of $I=1$, and a non-zero quadrupole interaction. Due to the isotopic abundances we identify this nucleus as a single nitrogen atom, eliminating hydrogen as a possibility. The defect possesses monoclinic [$\mathrm{C}_{\mathrm{1h}}$]{} symmetry and a small hyperfine interaction 