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Register a new userFourier-transform spectroscopy and relativistic electronic structure calculation on the $c^3Sigma^+$ state of KCs
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Added by
Alexander Oleynichenko
Publication date
2021
fields
Physics
and research's language is
English
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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)].
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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 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.
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.
Roles of electron correlation effects in the determination of attachment energies, magnetic dipole hyperfine structure constants and electric dipole (E1) matrix elements of the low-lying states in the singly charged cadmium ion (Cd$^+$) have been analyzed. We employ the singles and doubles approximated relativistic coupled-cluster (RCC) method to calculate these properties. Intermediate results from the Dirac-Hartree-Fock approximation, second-order many-body perturbation theory and considering only the linear terms of the RCC method are given to demonstrate propagation of electron correlation effects in this ion. Contributions from important RCC terms are also given to highlight importance of various correlation effects in the evaluation of these properties. At the end, we also determine E1 polarizabilities ($alpha^{E1}$) of the ground and $5p ^2P_{1/2;3/2}$ states of Cd$^+$ in the {it ab initio} approach. We estimate them again by replacing some of the E1 matrix elements and energies from the measurements to reduce their uncertainties so that they can be used in the high precision experiments of this ion.
Precise potentials for the ground state X1Sigma+g and the minimum region of the excited state 2_1Sigma+u of Sr2 are derived by high resolution Fourier-transform spectroscopy of fluorescence progressions from single frequency laser excitation of Sr2 produced in a heat pipe at 950 Celsius. A change of the rotational assignment by four units compared to an earlier work (G. Gerber, R. Moller, and H. Schneider, J. Chem. Phys. 81, 1538 (1984)) is needed for a consistent description leading to a significant shift of the potentials towards longer inter atomic distances. The huge amount of ground state data derived for the three different isotopomers 88Sr2, 86Sr88Sr and 87Sr88Sr (almost 60% of all excisting bound rovibrational ground state levels for the isotopomer 88Sr2) fixes this assignment undoubtedly. The presented ground state potential is derived from the observed transitions for the radial region from 4 to 11 A (9 cm-1 below the asymptote) and is extended to the longe range region by the use of theoretical dispersion coefficients together with already available photoassociation data. New estimations of the scattering lengths for the complete set of isotopic combinations are derived by mass scaling with the derived potential. The data set for the excited state 2_1Sigma+u was sufficient to derive a potential energy curve around the minimum.
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