Observation of gerade Rydberg state of Cd2 van der Waals complex cooled in free-jet expansion beam and excited using optical-optical double resonance method

We report on the observation of a gerade Rydberg electronic energy state of Cd₂ van der Waals (vdW) complex vibrationally cooled in a free-jet expansion beam. Cd₂ in the beam were excited from the X¹0_g⁺(5¹S₀) ground via the b³0_u⁺(5³P₁) intermediate to the final gerade state using optical–optical double resonance (OODR) method. A pronounced vibrational progression with partly resolved isotopologue components was recorded and analyzed. The analysis of isotopic separation indicated the excitation to high vibrational levels (v' ≈ 50). A comparison with the result of ab initio calculations reveals, that Cd₂ was most probably excited to the ³1_g -state correlating with the 6³S₁ atomic asymptote.