Hyperfine splitting and isotope shift in the atomic $D_2$ line of $^{22,23}$Na and the quadrupole moment of $^{22}$Na

The hyperfine structure of the $D_2$ optical line in $^{22}$Na and $^{23}$Na has been investigated using high resolution laser spectroscopy of a well-collimated atomic beam. The hyperfine splitting constants $A$ and $B$ for the excited $3p$ $^2P_{3/2}$ level for both investigated sodium isotopes have been obtained. They are as follows: $A(22) = 7.31(4)$ MHz, $B(22) = 4.71(28)$ MHz, $A(23) = 18.572(24)$ MHz, $B(23) = 2.723(55)$ MHz. With this data, using the high precision MCHF calculations for the electric field gradient at the nucleus, the electric quadrupole moment of $^{22}$Na has been deduced: $Q_s(22) = + 0.185(11)$ b. The sign of $Q_s(22)$, determined for the first time, indicates a prolate nuclear deformation. A precise value of the isotope shift $^{22,23}$Na in the $D_2$ line has also been obtained