Experimental studies of the NaK $1 3Δ$ state Available to Purchase

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 $∼0.0111 cm−1.$