Experimental studies of the NaK 1 3Δ state

Abstract

The NaK 1 3Δ state has been studied by the perturbation-facilitated optical–optical double resonance technique. Mixed singlet–triplet levels, A(2)1Σ+(vA,J)∼b(1)3Π(vb,J), were pumped from thermally populated rovibrational levels of the ground state, X(1)1Σ+(vX,J±1), using a single-mode cw dye laser. A single-mode cw Ti:Sapphire laser was then used to further excite the NaK molecules to various 1 3Δ(vΔ,NΔ,JΔ) rovibrational levels which were detected by observing collision-induced Λ3→a(1)3Σ+ fluorescence in the green part of the spectrum. The measured energies of the 1 3Δ(vΔ,NΔ) levels were fit to a Dunham expansion, and the Dunham coefficients were used to construct the RKR potential curve. Absolute numbering of the 1 3Δ state vibrational levels was established by a comparison of experimental and calculated 1 3Δ(vΔ,NΔ,JΔ)←b(1)3Π(vb,Jb) absorption line strengths. A deperturbation program was used to determine the vibration-dependent 1 3Δ state spin–orbit interaction parameter. Hyperfine structure of the 1 3Δ state was studied, and the Fermi-contact interaction term for this state was determined to be ∼0.0111 cm−1.