O. Nikolayeva

Lifetimes and transition dipole moment functions of NaK low lying singlet states: Empirical and ab initio approach

The paper presents experimental D 1∏ state lifetime τv′J′ data and develops empirical and ab initio approaches concerning D 1∏ and B 1∏ lifetimes, as well as D 1∏–X 1∑+, B 1∏–X 1∑+ and D 1∏–A 1∑+ transition dipole moment functions μ(R) of the NaK molecule. Experimental D 1∏(v′,J′) state τv′J′ values for v′ varying from 1 to 22 have been obtained from experimentally measured electric radio frequency-optical double resonance (rf-ODR) signal contours. The rf-ODR signals have been produced by D 1∏←X 1∑+ laser induced optical transition and rf field (1–900 MHz) induced e–f transition within the D 1∏(v′,J′) level. The possibility to determine empirical absolute μ(R) function in a wide R range from experimental τv′J′ dependence on v′ and J′ has been demonstrated; such an approach has been applied to obtain μ(R) for the B 1∏–X 1∑+ transition on which relative intensity data are absent. The empirical D 1∏–X 1∑+μ(R) function has been considerably improved by simultaneous fitting of relative intensity and lifetime d...

Fourier-transform spectroscopy and coupled-channels deperturbation treatment of the A 1 Σ + – b 3 Π complex of KCs

The laser induced fluorescence (LIF) spectra A1Sigma ~ b3Pi --> X1Sigma+ of KCs dimer were recorded in near infrared region by Fourier Transform Spectrometer with a resolution of 0.03 cm-1. Overall more than 200 LIF spectra were rotationally assigned to 39K133Cs and 41K133Cs isotopomers yielding with the uncertainty of 0.003-0.01 cm-1 more than 3400 rovibronic term values of the strongly mixed singlet A1Sigma+ and triplet b3Pi states. Experimental data massive starts from the lowest vibrational level v_A=0 of the singlet and nonuniformly cover the energy range from 10040 to 13250 cm-1 with rotational quantum numbers J from 7 to 225. Besides of the dominating regular A1Sigma+ ~ b3P Omega=0 interactions the weak and local heterogenous A1S+ ~ b3P Omega=1 perturbations have been discovered and analyzed. Coupled-channel deperturbation analysis of the experimental 39K133Cs e-parity termvalues of the A1S+ ~ b3P complex was accomplished in the framework of the phenomenological 4 x 4 Hamiltonian accounting implicitly for regular interactions with the remote states manifold. The resulting diabatic potential energy curves of the interacting states and relevant spin-orbit coupling matrix elements defined analytically by Expanded Morse Oscillators model reproduce 95% of experimental data field of the 39K133Cs isotopomer with a standard deviation of 0.004 cm-1 which is consistent with the uncertainty of the experiment. Reliability of the derived parameters was additionally confirmed by a good agreement between the predicted and experimental termvalues of 41K133Cs isotopomer. Calculated intensity distributions in the A ~ b --> X LIF progressions are also consistent with their experimental counterparts.

Permanent electric dipoles in B 1Π and D 1Π states of NaRb: Experiment and theory

The paper presents experimentally obtained permanent electric dipole moment values (μ) in electronically excited B 1Π and D 1Π states of 23Na85Rb and 23Na87Rb isotopomer molecules for a number of vibrational and rotational levels (v′,J′). The method is based on measuring relative intensities of “forbidden” fluorescence lines appearing due to dc Stark effect induced e/f parity mixing for a particular (v′,J′)-level, combined with electric radio frequency–optical double resonance measurement of Λ-splitting energy Δe,f. The measured D 1Π state μ values are close to 6 D, representing minor changes with the vibrational level v′ varying from 0 to 12 and J′ in the region between 7 and 50, while the measured B 1Π state μ values are about 3 D for v′=4, 5 and 6. The X 1Σ+, B 1Π, and D 1Π dipole moment functions μ(R) are calculated ab initio using the many body multipartitioning perturbation theory for explicit treatment of core-valence correlations. The theoretical and experimental dipole moment estimates are in a p...

NaK D1Π electric dipole moment measurement by Stark level crossing and e–f mixing spectroscopy

The paper presents the first permanent electric dipole moment dp measurements for NaK D1Π state rovibronic levels. Two different methods were applied to obtain dp values. Stark effect induced level crossing registered as the changes of fluorescence linear polarization P(E) with external electric field E yielded from one fit both the electric dipole moment value and the Λ-doubling splitting between e,f substates of an individual rotational state. Another method consisted of obtaining the ratio ΔefJ/dp from E-dependence of the forbidden line appearing in fluorescence as a result of e–f Stark mixing, along with direct ΔefJ measurement by RF – optical double resonance. The respective dipole moment values obtained are 5.9 – 6.4 D for the state v=7, J=23, as well as 4.5 – 4.8 D for v=12, J=7, the typical errors being ca. 12%–20%. The dp value for the latter state reflects dp diminution expected due to the admixture of the d3Π state caused by intramolecular interaction. Signal simulation and data fitting have be...

Fourier-transform spectroscopy of (4)1Σ+ → A 1Σ+ − b 3Π, A 1Σ+ − b 3Π → X1Σ+, and (1)3Δ1→bΠ0±3 transitions in KCs and deperturbation treatment of A 1Σ+ and b 3Π states

High resolution Fourier-transform spectroscopy data of term values in the spin-orbit (SO) coupled first excited A(1)Σ(+) and b(3)Π states in KCs were obtained from (4)(1)Σ(+) → A(1)Σ(+) - b(3)Π, A(1)Σ(+) - b(3)Π → X(1)Σ(+), and (1)(3)Δ1→b(3)Π(0(±)) spectra of laser-induced fluorescence (LIF). About 3000 new rovibronic term values of the A(1)Σ(+) and b(3)Π(Ω) states were obtained with an uncertainty about 0.01 cm(-1) and added to the previously obtained 3439 term values in Kruzins et al. [Phys. Rev. A 81, 042509 (2010)] and 30 term values of the b(3)Π(0(+)) state levels below the A(1)Σ(+) state in Tamanis et al. [Phys. Rev. A 82, 032506 (2010)]. The data field was extended considerably, going down to vibrational level v(b) = 0 and up in energy to 13,814 cm(-1), as compared to previously achieved v(b) = 14 and E = 13,250 cm(-1). Overall 6431 e-symmetry term values of (39)K(133)Cs were included in 4 × 4 coupled-channel deperturbation analysis. The analytical Morse-Long-Range (MLR) function yielded empirical diabatic potentials for the A(1)Σ(+) and b(3)Π(0(+)) states while the morphing of the SO ab initio points [J. T. Kim et al., J. Mol. Spectrosc. 256, 57 (2009)] provided the empirical diagonal and off-diagonal SO functions. Overall 98.5% of the fitted term values were reproduced with a rms (root mean square) uncertainty of 0.004 cm(-1). The reliability of the model is proved by a good agreement of predicted and measured term values of the (41)K(133)Cs isotopologue, as well as of measured and calculated intensities of (4)(1)Σ(+) → A(1)Σ(+) - b(3)Π LIF progressions. Direct-potential-fit of low-lying v(b) levels of the b(3)Π(0(-)) component yielded the MLR potential which represents the 204 f-symmetry experimental term values with a rms uncertainty of 0.002 cm(-1). The Ω-doubling of the b(3)Π0 sub-state demonstrates a pronounced vb-dependent increase.

Experimental and theoretical studies of Λ doublings and permanent electric dipoles in the low-lying Π1 states of NaCs

We present experimental data on the electric permanent dipole moments d(υ′,J′) and Λ splittings (q factors) in the quasidegenerate (3)Πe∕f1 state of the NaCs molecule over a wide range of the vibrational (υ′) and rotational (J′) quantum numbers by using the combination of dc Stark mixing and electric radio frequency-optical double resonance methods. Within the experimental (3)Π1 state υ′ ranged from υ′=0 to 34, q values exhibited a pronounced decrease from 7.91×10−6to0.47×10−6cm−1, while ∣d∣ values varied between 8.0 and 5.0D. Experimental evaluation yielded small d values about 1D for D(2)Π1 state υ′<3 levels. The experiment is supported by ab initio electronic structure calculations performed for the (1–3)Π1 states of NaCs by means of the many-body multipartitioning perturbation theory of potential energy curves, permanent dipole, and angular coupling matrix elements for the lowest singlet states. The predicted d values reproduce their experimental counterparts within the measurement errors while theore...

Energy and radiative properties of the (3)Π1 and (5)Σ+1 states of RbCs: Experiment and theory

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{\Pi} and (5)1{\Sigma}+ states of the RbCs molecule. The laser-induced (5)1{\Sigma}+(4)1{\Sigma}+(3)1{\Pi}-A(2)1{\Sigma}+ b(1)3{\Pi} fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer in the frequency range {\nu} 5500 to 10000cm-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 A1{\Sigma}+ and b3(\Pi) 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 a coupled-channels approach for both 85Rb133Cs and 87Rb133Cs isotopologs 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(\Pi) and (5)1{\Sigma}+ states were involved in a direct-potential-fit analysis performed in the framework of inverted perturbation approach. Quasirelativistic ab initio calculations of the spin-allowed (3)1{\Pi},(5)1{\Sigma}+- (1-4)1{\Sigma}+(1-3)1{\Pi} transition dipole moments were performed. Radiative lifetimes and vibronic branching ratios of radiative transitions from the (3)1{\Pi} and (5)1{\Sigma}+ states were evaluated. To elucidate the origin of the {\Lambda}-doubling effect in the (3)1{\Pi} state, the angular coupling (3)1{\Pi}-(1-5)1{\Sigma}+ electronic matrix elements were calculated and applied for the relevant q-factors estimate. The intensity distributions simulated for the particular (5)1{\Sigma}+(3)1{\Pi}-A-b LIF progressions have been found to be remarkably close to their experimental counterparts.

X {sup 1}SIGMA{sup +} and a {sup 3}SIGMA{sup +} states of the atom pair K+Cs studied by Fourier-transform spectroscopy

A comprehensive study of the X {sup 1}SIGMA{sup +} and a {sup 3}SIGMA{sup +} electronic states of the K and Cs atom pair is presented. Abundant spectroscopic data include 1937 transitions to the a {sup 3}SIGMA{sup +} state and 13 724 transitions to the X {sup 1}SIGMA{sup +} state for {sup 39}K {sup 133}Cs which were obtained by Fourier-transform spectroscopy. From these data potential energy curves were constructed simultaneously for both states X {sup 1}SIGMA{sup +} and a {sup 3}SIGMA{sup +} which are coupled by the hyperfine interaction. This allows us to accurately model the potential close to K(4s)+Cs(6s) atom-pair asymptote which is required to simulate cold collision processes. Dissociation energies of the X {sup 1}SIGMA{sup +} state as D{sub e}{sup X}=4069.208(40) cm{sup -1} and of the a {sup 3}SIGMA{sup +} state as D{sub e}{sup a}=267.141(20) cm{sup -1} were determined. Scattering lengths are predicted for different KCs isotopologs and Feshbach resonances were calculated for magnetic fields up to 1000 G.

Electric field induced alignment-orientation conversion in diatomic molecules: analysis and observation for NaK

This article reports the observation of the molecular fluorescence circularity under irradiation with linearly polarised light. This alignment-orientation conversion phenomenon arises as a result of partial transformation from alignment of the ensemble of 1 P state molecular angular momenta into their orientation under the effect of non-linear dc Stark effect. Circularity rate up to 0.12 was observed in D 1 P! X 1 S fluorescence of 23 Na 39 K molecules in agreement with the theoretically predicted value.

Studies of rotational level Λ-doubling by rf-optical double resonance spectroscopy: application to NaK D1Π

Abstract We report here the application of optical-radio frequency double resonance spectroscopy for individual rotational levels of the NaK D 1 Π state. Lambda doubling constant q values for five ν′, J ′ levels are obtained. These data are combined with measurements of dc e - f Stark-mixing-induced changes in optical spectra, and the electric dipole moment d p in the D 1 Π state is determined.