Experimental Study of the 4$^{\mathrm{3}}\Sigma _{\mathrm{g}}^{\mathrm{+}}$ and 3$^{\mathrm{3}}\Pi_{\mathrm{g}}$ States of Rubidium Dimer*

We reports a high-resolution experimental study and a numerical analysis of the 4$^{\mathrm{3}}\Sigma_{\mathrm{g}}^{\mathrm{+}}$ and 3$^{\mathrm{3}}\Pi_{\mathrm{g}}$ electronic states of rubidium dimer. In the experiment the Rb$_{\mathrm{2}}$ molecules were initially excited from the ground X$^{\mathrm{1}}\Sigma_{\mathrm{g}}^{\mathrm{+}}$ state to an intermediate level of the mixed A$^{\mathrm{1}}\Sigma _{\mathrm{u}}^{\mathrm{+}}$\textasciitilde b$^{\mathrm{3}}\Pi _{\mathrm{u}}$ manifold using a narrow band tunable TiSa laser. In the next step the probe laser, a narrow band dye laser tunable in the 13000-14000cm$^{\mathrm{-1\thinspace }}$range, excited the molecules further to the target states. The resonances of the probe laser were observed by detecting the total fluorescence from the excited states to the a$^{\mathrm{3}}\Sigma_{\mathrm{u}}^{\mathrm{+}}$ state in the 500nm range. Large number of ro-vibrational term values spanning a wide range of the rotational and vibrational quantum numbers were measured using the optical-optical double resonance technique. Besides the term values, we observed the resolved fluorescence intensities with Condon structures from many of the levels. The Rydberg--Klein--Rees (RKR) potential energy curves were constructed and optimized to reproduce the experimental data reliably.