Knowledge Bank

Highly excited vibrational levels of the $Na2A1\Sigma u+$ state are observed from $v=62$ to $v=131$. The highest level of excitation corresponds to a binding energy of 0.65% of the potential well depth, a classical outer turning point $R+\sim 19.1AA$ in contrast with $R+(v=0)\sim 3.8\backslash AA$, and a vibrational frequency of $\omega \sim 4.6cm-1$ in contrast with $\omega e\sim 117cm-1$ These excited levels have poor Franck-Condon factors with thermally populated levels of the ground $X1\Sigma g+$ electronic state. Therefore, modulated gain spectroscopy (MGS) is based upon a triple resonance excitation scheme where $Na2$ is used as a gain medium in an optically-pumped-laser (OPL) to transfer thermal population, state-selectively, to high v of the ground state. Transitions from these high v levels of the X-state to high v levels of the A-state have good vibrational overlaps and are excited with a third laser. These absorption resonances are monitored by detecting increases in the saturated gain of the OPL. The three cw lasers are each independently frequency stabilized, resulting in a frequency accuracy of $\pm 0.005cm-1$. A ``long range'' analysis of the vibrational and rotational levels determines the Van der Waals coefficients $C3,C6$, and $C8$. These reflect the atomic properties of $Na(32S1/2)$ and $Na(32P3/2)$ states into which the A-state dissociates, such as the transition dipole moments, dipole polarizabilities, and quadrupole polarizabilities. From the $Cn$-values, we have determined the most accurate value to date of the oscillator strength for the $Na(\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}S\to \mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}P)$ D lines as well as the dipole polarizability of the $Na(\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}P)$ state.