Improved rotational characterization of the E3Σ1(63S1) Rydberg state of CdAr van der Waals diatom: Excitation of single-isotopologue and J-levels population distribution

An improved rotational characterization of the E³Σ₁⁺(6³S₁) Rydberg state of the CdAr diatom produced in a supersonic beam and studied using LIF excitation spectra is presented. As an example, the spectra of the E³Σ₁⁺←A³Π_0⁺(5³P₁) transition, originating from the excitation of a single ¹¹⁶Cd⁴⁰Ar isotopologue, are recorded and analyzed. In the experiment, optical-optical double resonance method is employed, utilizing the E³Σ₁⁺(v′)←A³Π_0⁺(v′′=6)←X¹Σ_0⁺(v=0) scheme. The excitation of a single isotopologue and the influence of the first- step excitation wavenumber on rotational levels population distribution is carefully investigated facilitating the simulation of the recorded rotational profiles. Spectra of several v′←v′′=6 vibrational components are measured. Their analysis resulted in the determination of B_e′, α_e′ and β_e′ rotational constants. Additionally, R_e′ bond length in the E³Σ₁⁺ in Rydberg-state inner well of the ¹¹⁶Cd⁴⁰Ar was determined. For comparison, LIF excitation spectra in multi-isotopologue excitation are discussed.