Doppler-free optical-optical double resonance polarization spectroscopy of the Cs2 (2)3Π+u, (2)3Π1u, C 1Πu, and 1u[(2)3Σu++(2)3Πu] states

Abstract

High resolution spectra of the (2)3Πu[Ω=0+ and 1](v,J)←X 1Σg+(v″,J″) transitions of the Cs2 molecule in the 15 400−16 000 cm−1 region are measured by the technique of Doppler-free optical-optical double resonance polarization spectroscopy (OODRPS). Molecular constants of the (2)3Π0+u(v=0−18) and (2)3Π1u(v=0−13) levels are determined, and potential energy curves are constructed by the RKR method. The RKR potentials are found to be in very good agreement with the ab initio potentials computed by Spies. OODRPS spectra of the C 1Πu(v′=19−21,J′)←X 1Σg+ transitions are measured in order to expand the data on the C 1Πu state. We reconsider the perturbation of the C 1Πu(v′⩾13,J′) levels, and the perturbing state is identified as the 1u[(2)3Σu++(2)3Πu] state. The molecular constants of the perturbing state are determined to be Te=16 332.3 cm−1, ωe=21.9 cm−1, and Be=0.007 94 cm−1, and the potential is constructed by the RKR method. Energy shifts of both e and f levels of the C 1Πu state centered at the same J and the hyperfine splittings are identified as the results of spin-orbit coupling between the C 1Πu and 1u[(2)3Σu++(2)3Πu] states. Another type of energy shifts observed in only f level of the C 1Πu state is identified as the results of the L-uncoupling interaction between the (2)3Σu+[0u−(c)] state and the C 1Πu state which is mixed with the (2)3Πu[1u(a)] state by spin-orbit coupling. Line broadenings observed in the C 1Πu(v′⩾16) levels are identified as originating from the predissociation, which arises from interactions with the repulsive part of the 1u(a) state which has the potential hill with a peak of 16 420 cm−1 at about 6.6 Å.