Deperturbation treatment of the Α1Σ+-b 3Π complex of NaRb and prospects for ultracold molecule formation in X1Σ+(v=0;J=0)

High resolution Fourier transform spectra (FTS) of laser induced fluorescence (LIF) of C (1)Sigma(+);D (1)Pi -> A (1)Sigma(+)-b (3)Pi and A (1)Sigma(+)-b (3)Pi -> X (1)Sigma(+) transitions in (NaRb)-Rb-85 and (NaRb)-Rb-87 were obtained. An analysis of the direct LIF spectra together with the rotational relaxation satellites provided highly accurate rovibronic term values for (4 <= J <= 163) of the A (1)Sigma(+)-b (3)Pi complex, covering about 1950 mostly singlet levels 0 <= v(A)<= 49 and a considerable number (>360) of the predominantly triplet b (3)Pi(0,1) sublevels. The direct deperturbation analysis of the singlet-triplet A-b complex was performed by means of the inverted channel-coupling approach with Hund's coupling case a basis functions. The electronic matrix elements of the model 4x4 Hamiltonian were defined as piecewise analytical functions of the internuclear distance. Besides the Born-Oppenheimer potential energy curves of the mutually perturbed states and the off-diagonal spin-orbit (SO) A-b coupling function, the SO splitting of the b (3)Pi state was determined due to the pronounced electronic-rotation interaction between the b (3)Pi(0) and b (3)Pi(1) components observed for high J levels. Overall, 24 mass-invariant fitting parameters have been required to reproduce about 2300 experimental term values of both isotopomers with a standard deviation of 0.012 cm(-1), which is consistent with the uncertainty of the FTS experiment. An analytical mapping procedure based on a reduced variable representation of the radial coordinate was used to diminish the computational effort for the uniform finite-difference grid solution of the coupled-channel equations. The derived nonadiabatic A-b wave functions were used to evaluate the A (1)Sigma(+)-b (3)Pi-D (1)Pi, a (3)Sigma(+), X (1)Sigma(+) rovibronic transition probabilities. The relative intensity distributions predicted for the D -> A-b and A-b -> X LIF progressions agree with their experimental counterparts within the accuracy of the measurements. The calculated A-b-a, X transition probabilities were applied for simulation of the stimulated Raman a -> A-b -> X processes, which can lead to efficient formation of ultracold NaRb molecules in the ground level v(X)=0; J(X)=0.