Doppler-free high-resolution continuous-wave optical UV spectroscopy on the A2Σ+←X2Π3/

We report on Doppler-free continuous-wave optical UV spectroscopy resolving the hyperfine structure of the $A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}\ensuremath{\leftarrow}X{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{3/2}$ transition in nitric oxide for total angular momenta ${J}_{X}=1.5--19.5$ on the ${\mathrm{oP}}_{12\mathrm{ee}}$ branch. The resulting line splittings are compared to calculated splittings and fitted determining new values for the molecular constants $b$, $c$, $eQ{q}_{0}$, and ${b}_{F}$ for the $A{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state. The constants are in good agreement with values previously determined by quantum beat spectroscopy.