Energy and radiative properties of the (3)Π1 and (5)Σ

Abstract

We combined high resolution Fourier-transform spectroscopy and large scale electronic structure calculation to study energy and radiative properties of the high-lying (3) 1 Π and (5) 1 Σ + states of the RbCs molecule. The laser induced (5) 1 Σ + ,(4) 1 Σ + ,(3) 1 Π →A(2) 1 Σ + ∼ b(1) 3 Π fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer in the frequency range ν ∈ [5500, 10000] cm −1 with the instrumental resolution of 0.03 cm −1 . The rotational assignment of the observed LIF progressions, which exhibit irregular vibrational -rotational spacing due to strong spin-orbit interaction between A 1 Σ + and b 3 Π states was based on the coincidences between observed and calculated energy differences. The required rovibronic term values of the strongly perturbed A∼b complex have been calculated by coupled -channel approach for both 85 Rb 133 Cs and 87 Rb 133 Cs isotopolgues with accuracy of about 0.01 cm −1 , as demonstrated in [A. Kruzins et. al., J. Chem. Phys. 141,184309 (2014)]. The experimental energies of the upper (3) 1 Π and (5) 1 Σ + states were involved in a direct-potential-fit analysis performed in the framework of inverted perturbation approach. Quasi-relativistic ab initio calculations of the spin-allowed (3) 1 Π,(5) 1 Σ + → (1-4) 1 Σ + ,(1-3) 1 Π transition dipole moments were performed. Radiative lifetimes and vibronic branching ratios of radiative transitions from (3) 1 Π and (5) 1 Σ + states were evaluated. To elucidate the origin of the Λ-doubling effect in the (3) 1 Π state the angular coupling (3) 1 Π-(1-5) 1 Σ + electronic matrix elements were calculated and applied for the relevant q−factors estimate. The intensity distributions simulated for the particular (5) 1 Σ + ;(3) 1 Π →A∼b LIF progressions have been found to be remarkably close to their experimental counterparts.

Fourier-transform spectroscopy, direct potential fit, and electronic structure calculations on the entirely perturbed (4)1Πstate of RbCs

“…The predicted τ -values are by about 10 and 2 times smaller than the τ -values calculated in Ref. [16] for the (3) 1 Π and (5) 1 Σ + states, respectively. Furthermore, in contrast to the increasing τ -values of the (4) 1 Π state, the radiative lifetimes of both (3) 1 Π and (5) 1 Σ + states are rapidly decreasing with growing v ′ .…”

“…As expected, the dominant decay channel of the(4) 1 Π state is the infrared (IR) transition to the A ∼ b complex. However, in contrast to the case of (3) 1 Π and (5) 1 Σ + states [16], the decay rate to the ground X 1 Σ + state is only two times smaller than to the A ∼ b complex, therefore the visible (4) 1 Π → X 1 Σ + LIF could be easily observed. The contribution of the far IR (4) 1 Π → B, D 1 Π transitions is almost the same as of transitions to the ground state, the (4) 1 Π → D 1 Π channel being more efficient than the (4) 1 Π → B 1 Π channel.…”

“…was determined from calculated term values E A∼b of the A 1 Σ + ∼ b 3 Π complex, which, according to Refs. [16,18],…”

“…[15]. In our recent work [16] we studied the (3) 1 Π state of RbCs converging to the Rb(5 2 S) + Cs(5 2 D) asymptotic limit of separated atoms at about 18 400 cm −1 , as well as the (5) 1 Σ + state converging to the Rb(5 2 S) + Cs(7 2 S) at about 22 400 cm −1 .…”

Fourier transform spectroscopy, relativistic electronic structure calculation, and coupled-channel deperturbation analysis of the fully mixed $A^1Σ^+_u$ and $b^3Π_u$ states of Cs$_2$

“…In particular, the accuracy and abundance of information on A ∼ b system of RbCs allowed us to assign laser induced fluorescence (LIF) transitions from higher-excited electronic states to the A ∼ b complex in case when the respective LIF to the ground X-state was too weak to be observed, see Ref. [17]. The generated comprehensive set of RbCs A ∼ b term values was helpful to predict the A ∼ b ← X transition frequencies to be used for two-step laser excitation of the (4) 1 Π state [18].…”