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Register a new userFourier transform spectroscopy, relativistic electronic structure calculation, and coupled-channel deperturbation analysis of the fully mixed $A^1Sigma^+_u$ and $b^3Pi_u$ states of Cs$_2$
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Artis Kr\\=uzi\\c{n}\\v{s}
Publication date
2019
fields
Physics
and research's language is
English
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The 4503 rovibronic term values belonging to the mutually perturbed $A^1Sigma^+_u$ and $b^3Pi_u$ states of Cs$_2$ were extracted from laser induced fluorescence (LIF) $Asim brightarrow X^1Sigma^+_g$ Fourier transform spectra with the 0.01 cm$^{-1}$ uncertainty. The experimental term values of the $A^1Sigma^+_usim b^3Pi_u$ complex covering the rotational levels $Jin [4,395]$ in the excitation energy range $[9655,13630]$ cm$^{-1}$ were involved into coupled-channel (CC) deperturbation analysis. The deperturbation model takes explicitly into account spin-orbit coupling of the $A^1Sigma^+_u(A0^+_u)$ and $b^3Pi^+_{0_u}(b0^+_u)$ states as well as spin-rotational interaction between the $Omega=0$, $1$ and $2$ components of the $b^3Pi^+_{Omega_u}$ state. The emph{ab initio} relativistic calculations on the low-lying electronic states of Cs$_2$ were accomplished in the framework of Fock space relativistic coupled cluster (FSRCC) approach to provide the interatomic potentials of the interacting $A0^+_u$ and $b0^+_u$ states as well as the relevant $Asim b$ spin-orbit coupling function. To validate the present CC deperturbation analysis solely obtained by energy-based data, the $Asim b to X(v^{primeprime}_X)$ LIF intensity distributions were measured and compared with their theoretical counterparts obtained by means of the non-adiabatic vibrational wave functions of the $Asim b$ complex and the FSRCC $Asim b to X$ transition dipole moments calculated by the finite-field method.
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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.
The Ti:Saphire laser operated within 13800 - 11800 cm$^{-1}$ range was used to excite the $c^3Sigma^+$ state of KCs molecule directly from the ground $X^1Sigma^+$ state. The laser-induced fluorescence (LIF) spectra of the $c^3Sigma^+ rightarrow a^3Sigma^+$ transition were recorded with Fourier-transform spectrometer within 8000 to 10000 cm$^{-1}$ range. Overall 673 rovibronic term values belonging to both $e/f$-components of the $c^3Sigma^+(Omega=1^{pm})$ state of $^{39}$KCs, covering vibrational levels from $v$ = 0 to about 45, and rotational levels $Jin [11,149]$ were determined with the accuracy of about 0.01 cm$^{-1}$; among them 7 values for $^{41}$KCs. The experimental term values with $vin [0,22]$ were involved in a direct point-wise potential reconstruction for the $c^3Sigma^+(Omega=1^{pm})$ state, which takes into account the $Omega$-doubling effect caused by the spin-rotational interaction with the nearby $c^3Sigma^+(Omega=0^-)$ state. The analysis and interpretation were facilitated by the fully-relativistic coupled cluster calculation of the potential energy curves for the $B^1Pi$, $c^3Sigma^+$, and $b^3Pi$ states, as well as of spin-forbidden $c-X$ and spin-allowed $c-a$ transition dipole moments; radiative lifetimes and vibronic branching ratios were calculated. A comparison of relative intensity distributions measured in vibrational $c-a$ LIF progressions with their theoretical counterparts unambiguously confirms the vibrational assignment suggested in [emph{J. Szczepkovski, et. al.}, JQSRT, textbf{204}, 133-137 (2018)].
Accurate Fourier-transform spectroscopic absorption measurements of vacuum ultraviolet transitions in atomic nitrogen and carbon were performed at the Soleil synchrotron. For $^{14}$N transitions from the $2s^22p^3,^4$S$_{3/2}$ ground state and from the $2s^22p^3,^2$P and $^2$D metastable states were determined in the $95 - 124$ nm range at an accuracy of $0.025,mathrm{cm}^{-1}$. Combination of these results with data from previous precision laser experiments in the vacuum ultraviolet range reveal an overall and consistent offset of -0.04 wn from values reported in the NIST database. %The splitting of the $2s^22p^3,^4$S$_{3/2}$ -- %$2s2p^4,^4$P$_{5/2,3/2,1/2}$ The splittings of the $2s^22p^3,^4$S$_{3/2}$ -- $2s2p^4,^4$P$_{J}$ transitions are well-resolved for $^{14}$N and $^{15}$N and isotope shifts determined. While excitation of a $2p$ valence electron yields very small isotope shifts, excitation of a $2s$ core electron results in large isotope shifts, in agreement with theoretical predictions. For carbon six transitions from the ground $2s^22p^2,^3$P$_{J}$ and $2s^22p3s, ^3$P$_{J}$ excited states at $165$ nm are measured for both $^{12}$C and $^{13}$C isotopes.
We describe a modification of the inverted perturbation approach method allowing to construct physically sensible potential energy curves for electronic states of diatomic molecules even when some parts of the potential are not adequately characterized by the experimental data. The method is based on a simple regularization procedure, imposing an additional constraint on the constructed potential curve. In the present work it is applied to the double minimum 4$^1Sigma^{+}_{mathrm u}$ state of Na$_2$, observed experimentally by polarization labeling spectroscopy technique.
We observed the $A^1Sigma^+sim b^3Pito a^3Sigma^+/X^1Sigma^+$ laser-induced fluorescence (LIF) spectra of the RbCs molecule excited from the ground $X^1Sigma^+$ state by the Ti:Sapphire laser. The LIF radiation from the common perturbed levels of the singlet-triplet $Asim b$ complex was recorded by the Fourier-transform (FT) spectrometer with the instrumental resolution of 0.03~cm$^{-1}$. The relative intensity distribution in the rotationally resolved $Asim bto a^3Sigma^+(v_a)/X^1Sigma^+(v_X)$ progressions was measured, and their branching ratio was found to be about of 1$div$5$ times$10$^{-4}$ in the bound region of the $a^3Sigma^+$ and $X^1Sigma^+$ states. The experiment was complemented with the scalar and full relativistic calculations of the $A/b - X/a$ transition dipole moments (TDMs) as functions of internuclear distance. The relative systematic error in the resulting emph{ab initio} TDM functions evaluated for the strong $A - X$ transition was estimated as few percent in the energy region, where the experimental LIF intensities are relevant. The relative spectral sensitivity of the FT registration system, operated with the InGaAs diode detector and CaF beam-splitter, was calibrated in the range $[6~500,12~000]$~cm$^{-1}$ by a comparison of experimental intensities in the long $Asim bto X(v_X)$ LIF progressions of the K$_2$ and KCs molecules with their theoretical counterparts evaluated using the emph{ab initio} $A - X$ TDMs. Both experimental and theoretical transition probabilities can be employed to improve the stimulated Raman adiabatic passage process, $ato Asim b to X$, which is exploited for a laser assembling of ultracold RbCs molecules.
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