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 $\mathrm{A}\,^2\Sigma^+ \leftarrow \mathrm{X}\,^2\Pi_{3/2}$ transition in nitric oxide for total angular momenta $J_X=1.5-19.5$ on the $\mathrm{oP_{12ee}}$ branch. The resulting line splittings are compared to calculated splittings and fitted determining new values for the molecular constants $b, c, eQq_0$ and $b_F$ for the $\mathrm{A}\,^2\Sigma^+$ state. The constants are in good agreement with values previously determined by quantum beat spectroscopy.