Fourier-transform spectroscopy and deperturbation analysis of the spin-orbit coupled A1Σ+ and b3Π states of KRb

Abstract

Fourier-transform A(1)Σ(+) - b(3)Π → X(1)Σ(+) laser-induced fluorescence spectra were recorded for the natural mixture of (39,41)K(85,87)Rb isotopologues produced in a heatpipe oven. Overall 4200 rovibronic term values of the spin-orbit coupled A(1)Σ(+) and b(3)Π states were determined with an uncertainty of about 0.01 cm(-1) in the energy range [10 850, 14 200] cm(-1) covering rotational quantum numbers J' ∈ [3, 280]. Direct deperturbation analysis of the A ∼ b complex performed within the framework of the A(1)Σ(+) ∼ b(3)ΠΩ=0,1,2 coupled-channel approach reproduced experimental data with a standard deviation of 0.004 cm(-1). Initial parameters of the internuclear potentials and spin-orbit coupling functions along with the relevant transition dipole moments were obtained by performing the quasi-relativistic electronic structure calculations. The mass-invariant molecular parameters obtained from the fit were used to predict energy and radiative properties of the A ∼ b complex for low J levels of (39)K(85)Rb as well as for (41)K(87)Rb isotopologues, allowing us to identify the most reasonable candidates for the stimulated Raman transitions between the initial uppermost vibrational levels of the a(3)Σ(+) and X(1)Σ(+) states, the intermediate levels of the A ∼ b complex, and the lowest absolute ground X(1)Σ(+)(v = 0, J = 0) state.

Twofold diabatization of the KRb(1–2)Π1complex in the framework ofab initioand deperturbation approaches

“…The comprehensive set of non-relativistic PECs, permanent and transition dipole moments for the ground and excited states of KRb are available 11,[21][22][23][24][25] as well. The SOC effect has been included into ab initio calculations in Refs.…”

“…where the highly accurate empirical PEC U The details of the computational procedure used can be found elsewhere 24 . Briefly, the inner core shell of both potassium and rubidium atoms was replaced by energy-consistent non-empirical effective core potentials 32 (ECP), leaving 9 outer shell (8 sub-valence plus 1 valence) electrons for explicit treatment.…”

“…In the framework of the rigorous coupled-channel (CC) deperturbation model 24,36,37 , the non-adiabatic rovibronic energy E CC of the (1, 2) 1 Π complex is determined by the solution of the two coupled radial equations…”

“…The SOC effect has been included into ab initio calculations in Refs. 6,11,24,and 26. Among other alkali diatomics, the KRb molecule stands out because of the high density of the electronic states belonging to both singlet and triplet manifolds. This is attributed to the accidental close values of the ionization potential, electronic affinity and the polarizability of K and Rb atoms in their ground states as well as the almost degenerate energies of the first excited K(4 2 P) and Rb(5 2 P) states 27-29 .…”

“…The corresponding CPP cut-off radii of both atoms were adjusted to reproduce the experimental fine-structure splitting of the lowest excited K(4 2 P) and Rb(5 2 P) states 29 . The resulting MRCI wave functions were used to evaluate the permanent dipole functions d 1,2 (R) of adiabatic 1 1 Π and 2 1 Π states as well as the correspondingThe adiabatic matrix elements were transformed to the relevant diabatic moments µ 1,2 (R), µ 12 (R) asFinally, we have calculated spin-orbitIn the framework of the rigorous coupled-channel (CC) deperturbation model 24,36,37 , the non-adiabatic rovibronic energy E CC of the (1, 2) 1 Π complex is determined by the solution of the two coupled radial equationswhere µ is the reduced molecular mass, I is the identity matrix and V(R) is the symmetric matrix of the potential energy given bywhere the diabatic potentials V 1,2 (R) and electronic coupling matrix element V 12 (R) are the mass-invariant functions of internuclear distance R. The two-component 4 vibrational eigenfunction Φ in Eq. (9) is normalized for the bound states as i P i = 1, where…”