An example of the recorded LIF spectrum from the E(4)1Σ+ state excited by laser frequency 17 620.437 cm−1. The strongest LIF progression lines originating from the excited level with v′ = 25, J′ = 82 to the ground X(1)1Σ+ state within the range are marked in the figure. Weaker transitions to the a(1)3Σ+ state originating from the same excited level are seen at lower frequencies about 13 600 cm−1. The excitation laser and part of LIF is suppressed by a longpass edge filter for frequencies above 16 500 cm−1.
The data field of experimental rovibronic term values of the KCs E(4)1Σ+ state as a function of J′(J′ + 1) values. Black dots denote the experimental term values for 39K133Cs isotopologue, red crosses for 41K133Cs isotopologue, lines represent the term values from the empirical “spline-pointwise” IPA PEC calculated for each fifth vibrational level starting from v′ = 0.
Schema of the selected KCs electronic states. The ab initio PECs were calculated in pure (a) Hund's coupling case in Ref. 5. The shaded area depicts the energy range covered in the present experiment.
The vibrational quantum (a) and rotational constants (b) obtained for the 39K133Cs E(4)1Σ+ state in the framework of CPE, IPA, and Dunham models. The insets demonstrate declining of Dunham based estimates for v′ > 50.
The centrifugal distortion constants , , and estimated for the 39K133Cs E(4)1Σ+ state in the framework of CPE, IPA, and Dunham models.
The empirical mass-invariant potential energy curve derived for the KCs E(4)1Σ+ state in the framework of CPE model (4). Horizontal solid lines denote the present experimental energy region used for the construction.
Differences between the empirical E(4)1Σ+ state PEC and ab initio relativistic U ab (r) from Ref. 39 (a), as well as its present empirical (b), and (c) counterparts. Here U ab (r) was uniformly vertically shifted to match the experimental fine atomic asymptote K(42S1/2) + Cs(52D3/2).
Comparison (in log scale) of the coefficients derived for Chebyshev c k [Eq. (4)] and ordinary d k [Eq. (9)] polynomial expansion of the resulting CPE PEC as dependent on their ordering number k.
Normalized experimental and calculated by Eq. (13) intensity distributions in LIF progressions originating from v′ = 42, 48, and 55 vibrational levels of the upper E(4)1Σ+-state.
Experimental rovibronic term values of the 41K133Cs isotopologue of the E(4)1Σ+ state. δ values are the differences between the experimental energies and those predicted by means of empirical CPE and IPA PECs, as well as by conventional Dunham model [Eq. (1)], see Table II. All energies are in cm−1.
The mass-dependent 39K133Cs Dunham molecular constants Y ij and their uncertainties ΔY ij (in cm−1) of the E(4)1Σ+ state obtained in the framework of the unconstrained Dunham analysis [Eq. (1)] of the restricted 2 ⩽ v′ ⩽ 50 vibrational set of the present experimental rovibronic term values.
The position of the PEC minimum of the KCs E(4)1Σ+ state predicted in the framework of the empirical CPE, IPA, and Dunham models. The relativistic ab initio data are borrowed from Ref. 39. The electronic energy T e (in cm−1) refers to the minimum of the ground X-state, while the equilibrium distance r e is in Å.
The resulting mass-invariant parameters of the CPE potential for the KCs E(4)1Σ+ state defined by expression (4) on the semiinterval . The dissociation energy referring to the minimum of the ground X 1Σ+ state and the expansion coefficients c k are given in cm−1 while the and parameters in Å. Symbol † denotes the fixed parameters.
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