High resolution spectroscopy of B¹∏_u potential in Rb₂ molecule using a supersonic molecular beam

In this work, we present high resolution spectroscopy of Rb₂ molecules produced in a supersonic molecular beam. Molecular excitation is achieved using a CW diode laser operating near 682 nm, whose frequency is actively monitored by a calibrated wavelength meter. By scanning the laser approximately 7 cm^-1 below the bandhead, we excite rotational transitions belonging to the  X¹∑_g⁺(v_X=0)→B¹∏_u (v_B=1,2) and X¹∑_g⁺(v_X=1)→B¹∏_u (v_B=1) vibrational bands. Rovibrational lines corresponding to the isotopologues ⁸⁵Rb₂, ⁸⁵⁰Rb⁸⁷Rb, and ⁸⁷Rb₂ are clearly resolved and identified. Our measurements extend and refine earlier studies by C. Amiot and J. Vergès [Chem. Phys. Lett. 274, 91 (1997)] and by Caldwell et al. [Chem. Phys. 54, 31 (1980)], providing significantly higher spectral resolution. The experimental results are in excellent agreement with theoretical predictions and enable an improvement of the molecular constants by approximately one order of magnitude.