Fourier-transform spectroscopy and description of low-lying energy levels in the B(1)(1)Π state of RbCs

Production of ultracold 85Rb133Cs molecules in the lowest ground state via the B1Π1 short-range state

We investigate the production of cold ⁸⁵Rb¹³³Cs molecules in the lowest vibronic level of the ground electronic state via the B¹Π₁ short-range state. The photoassociation (PA) spectra of the B¹Π₁ state, including newly observed transition to 2 vibronic levels, are obtained by high sensitivity time-of-flight mass spectrometry. Based on these PA spectra, the harmonic and anharmonic constants of vibronic states are obtained, resulting in predicted vibronic energies with an uncertainty of 1-2 cm^-1. The B¹Π₁ (v = 3) state is found to have the maximum production rate for ground-state molecules with a value of 3(1) × 10⁴ s^-1, which is 3 times larger than the value via the previously studied 2³Π_0⁺ (v = 10, J = 0) state with two-photon cascade decay. The populations of J = 0, 1, and 2 rotational levels of X¹Σ⁺ (v = 0) state molecules formed via the B¹Π₁ (v = 3, J = 1) state are measured to be around 20%, 40%, and 20%. To quantify the coupling strength between the B¹Π₁ (v = 3) state and X¹Σ⁺ (v = 0) state, the transition dipole moment between them is measured to be 7.2(2) × 10^-3ea₀, which is also 3 times larger than the value between the 2³Π_0⁺ (v=10) state and X¹Σ⁺ (v = 0) state, meaning the B¹Π₁ (v = 3) state has a stronger coupling with the X¹Σ⁺ (v = 0) state. Our detailed measurements provide relevant parameters for investigation on direct stimulated Raman adiabatic passage transfer between the atomic scattering state and molecular bound state for ⁸⁵Rb¹³³Cs molecules.

Extended Fourier-transform spectroscopy studies and deperturbation analysis of the spin-orbit coupled A1Σ+ and b3Π states in RbCs

The article presents a study of the strongly spin-orbit coupled singlet A(1)Σ(+) and triplet b(3)Π states of the RbCs molecule, which provide an efficient optical path to transfer ultracold molecules to their rovibrational ground state. Fourier-transform A(1)Σ(+) - b(3)Π → X(1)Σ(+) and (4)(1)Σ(+) → A(1)Σ(+) - b(3)Π laser-induced fluorescence (LIF) spectra were recorded for the natural mixture of the (85)Rb(133)Cs and (87)Rb(133)Cs isotopologues produced in a heat pipe oven. Overall 8730 rovibronic term values of A(1)Σ(+) and b(3)Π states were determined with an uncertainty of 0.01 cm(-1) in the energy range [9012, 14087] cm(-1), covering rotational quantum numbers J ∈ [6, 324]. An energy-based deperturbation analysis performed in the framework of the four A(1)Σ(+) - b(3)Π(Ω = 0, 1, 2) coupled-channels approach reproduces 97% of the experimental term values of both isotopologues with a standard deviation of 0.0036 cm(-1). The reliability of the deperturbed mass-invariant potentials and spin-orbit coupling functions of the interacting A(1)Σ(+) and b(3)Π states is additionally proved by a good reproduction of the A - b → X and (4)(1)Σ(+) → A - b relative intensity distributions. The achieved accuracy of the A - b complex description allowed us to use the latter to assign the observed (5)(1)Σ(+) → A - b and (3)(1)Π → A - b transitions. As is demonstrated, LIF to the A - b complex becomes as informative as to the ground X(1)Σ(+) state, which is confirmed by comparing the results of (4)(1)Σ(+) state analysis based on (4)(1)Σ(+) → A - b LIF with the data from V. Zuters et al. [Phys. Rev. A 87, 022504 (2013)] based on (4)(1)Σ(+) → X LIF.