Аннотация:In heavy heteronuclear alkali diatomic molecules containing Rb and Cs atoms the lowest excited
A1Σ+ and b3Π states (A − b complex for short) are strongly coupled by spin-orbit (SO) interaction. An accurate description of such systems is a challenging task, which imposes a detailed experimental study and elaboration of a powerful deperturbation procedure. Recently this problem was successfully solved for NaRb [1], NaCs [2], KCs [3], RbCs [4] and Rb2 [5] molecules. In these studies the term values of the A−b complex were determined from laser induced fluorescence (LIF) spectra recorded by high resolution Fourier Transform (FT) spectrometer. The coupled-channel deperturbation analysis allowed reproducing the obtained data with experimental accuracy 0.01 cm−1.
The goal of the present work is to apply this approach for the KRb A−b complex. In the experiment KRb molecules were produced in a linear stainless steel heat pipe. The laser beam was sent into the heat pipe through a pierced mirror. The backwards LIF was collected by the same mirror and focused on the input aperture of the FT spectrometer Bruker IFS-125HR and recorded with a resolution of 0.03-0.05 cm−1. We used a direct (A1Σ+ −b3_) X1_+ excitation by diode lasers (980 - 1020 nm) and by Ti:Sph laser (Coherent MBR-110) followed by observation of the (A1Σ+ − b3Π) - X1Σ+ LIF. Overall more than 300 LIF spectra were recorded and 900 KRb progressions for 39K85Rb and 39K87Rb isotopologues were analyzed yielding more than 4000 term values of the A − b complex, including the data from collisional rotational energy transfer. The data field contains rovibronic levels with rotational quantum numbers J = [3, 279] in the energy range E = [10927, 14250] cm−1. A direct deperturbation treatment of the experimental rovibronic term values of both isotopologues of the mutually perturbed A1Σ+ and b3_ states was accomplished in the framework of inverted coupled-channel approach by means of the 4x4 Hamiltonian constructed in Hund’s (a) coupling case basis functions. The Expanded Morse Oscillator model was used to describe potential energy curves while for the SO coupling functions we adopted the "morphed" form of the relevant ab initio spin-orbit matrix elements. As a result, 44 mass-invariant fitting parameters of the corresponding functions have been required to reproduce 96% of experimental term values of the A − b complex with a standard deviation of 0.004 cm−1. The energy-based deperturbation analysis was additionally confirmed by a calculation of relative intensity distributions in the A − b - X LIF progressions.
The support from the Latvian Science Council Grant No. 119/2012 as well as from Latvian Ministry of Education and Science Grant No. 11-13/IZM14-12 is gratefully acknowledged. Moscow team thanks for the support by the RFBR grant No. 13-03-00446-a.
References
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[4]A. Kruzins et al. J. Chem. Phys. 141, 184309 (2014)
[5] A. N. Drozdova et al. Phys. Rev. A. 88, 022504 (2013)