Scheme of potential energy curves of the low-lying electronic states of the KCs molecule based on Hund's case “a” calculations in Ref. 7 (upper graph) and Hund's case “c” calculations in Ref. 8 (lower graph, where the letters at potentials are referring to the “a” case).
KCs LIF spectrum excited by laser frequency 14 090.268 cm−1 and recorded with a silicon detector. The spectrum contains only B → X transitions. The dominant progression originates from the v ′ = 3, J ′ = 129 level of the B(1)1Π state (line positions are marked below the spectrum). No spin-forbidden transitions to the a 3Σ+ state are observed.
KCs LIF spectrum excited by laser frequency 14 176.394 cm−1 and recorded with a silicon detector. The spectrum contains both spin-allowed B → X and spin-forbidden B → a transitions. The dominant KCs LIF progressions to the singlet and triplet states originate from the v ′ = 4, J ′ = 88 level of B(1)1Π state (line positions are marked with vertical lines below the spectrum). LIF lines close to exciting laser are weakened by a long-pass filter. The inset contains the B → a bands.
An example of the LIF intensity distribution over v ′′ in the B → X bands. (a) the LIF progression is excited at a laser frequency of 13 712.700 cm−1, assigned to the R-transition B(0, 119) ← X(4, 118). (b) the LIF progression is excited at a laser frequency of 14 071.926 cm−1, assigned to the Q-transition B(1, 51) ← X(0, 51).
An expanded example of rotational relaxation from the spectrum shown in Fig. 2. The portion of the spectrum presented corresponds to the B(3, 129) → X(12, 129) transition (most intense line). Q-, P-, and R-lines are marked by bars below the spectrum.
J ′-dependence of experimental term values in the reduced energy scale E red = E − 0.02J ′(J ′ + 1). Short arrows mark levels (0, 119) and (1, 51) producing the LIF intensity distributions shown in Fig. 4. Insets show term value plots of another state (most likely C(3)1Σ+) crossing the plots of B(1)1Π state at (2, 95) and (5, 144). v ′-numbering from 0 to 8 is indicated. Enlarged symbols (×) and red dotted lines represent term values of the C-state. The lowest v* term is constructed basing on perturbation centers at v ′ = 0, J ′ = 108 and v ′ = 1, J ′ = 63.
J ′-dependence of (a) the Λ-doubling constant q(v ′) and (b) the rotational constant for v ′ = 0.
J ′-dependence of the differences between measured term values and their counterparts calculated using the data from Tables I and II. Horizontal lines indicate experimental uncertainty ±0.01 cm−1. Arrow marks the level (2, 94).
(a) Example of B → X LIF spectra exhibiting weak LIF lines around 11 280 cm−1. LIF progressions from directly excited B 1Π(v ′ = 2, J ′ = 94) level is marked by vertical bars below the spectrum; the inset expands the rotational relaxation pattern for v ′′ = 9 from the directly excited B 1Π(v ′ = 2, J ′ = 94) level. (b) Enlarged fragment of the spectrum around v ′′ = 50 and 51. LIF from directly excited level is marked by red vertical bars below the spectrum, collision-induced LIF from a state with J ′ = 94 is marked by blue dots above the spectrum. LIF from a directly excited C-state level is marked by an asterisk.
(a) v ′′-dependence of the relative intensities of C 1Σ+ → X 1Σ+ LIF. Red shaded bars represent the experiment, black bars are FCFs calculated using the C 1Σ+ PEC from Ref. 7; the data are matched at v ′′ = 50. (b) ΔG v dependence on the energy of the respective levels. Dots represent the experiment, lines are calculated from ab initio PECs (Refs. 6 and 7) (solid lines – for C 1Σ+, dotted lines – for c 3Σ+).
List of the grid points of the IPA potential for the KCs B(1)1Π state. Energies are given with respect to the minimum of the ground state.
The q 0 and q 1 values (in cm−1) fitted for the four lowest vibrational levels of the B(1)1Π state.
Comparison of experimental E expt and calculated (by pointwise PEC) rovibronic term values E calc for the 41K133Cs isotopologue of the B(1)1Π state. All energies are in cm−1.
Dunham coefficients Y ij obtained by fitting the data for v ′ ∈ [0, 3], J ′ ∈ [7, 233] of the B(1)1Π state of 39K133Cs. All values are in cm−1.
Molecular constants for particular v ′-levels of the B(1)1Π state of 39K133Cs. All values are in cm−1.
Molecular constants of the B(1)1Π state of 39K133Cs fitted in the present work compared with their ab initio counterparts. T e and ω e in cm−1, R e in Å.
Tentative molecular constants for the C-state, all values in cm−1. v* (see Fig. 6) is estimated as 18 ± 2 by comparing experimental intensity distribution (see Fig. 9(a)) and term values with calculations basing on Ref. 7.
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