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Register a new userThe branching ratio of intercombination $A^1Sigma^+sim b^3Pito a^3Sigma^+/X^1Sigma^+$ transitions in the RbCs molecule: measurements and calculations
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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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The intercombination $a^3Pi - X^1Sigma^+$ Cameron system of carbon monoxide has been computationally studied in the framework of multi-reference Fock space coupled cluster method with the use of generalized relativistic pseudopotential model for the effective introducing the relativity in all-electron correlation treatment. The extremely weak $a^3Pi_{Omega=0^+,1} - X^1Sigma^+$ transition probabilities and radiative lifetimes of the metastable $a^3Pi$ state were calculated and compared with their previous theoretical and experimental counterparts. The impact of a presumable variation of the fine structure constant $alpha=e^2/hbar c$ on transition strength of the Cameron system has been numerically evaluated as well.
Aluminum monochloride (AlCl) has been proposed as an excellent candidate for laser cooling. Here we present absorption spectroscopy measurements on the $A^1Pi leftarrow X^1Sigma^+$ transition in AlCl inside a cryogenic helium buffer-gas beam cell. The high resolution absorption data enables a rigorous, quantitative comparison with our high-level ab initio calculations of the electronic and rovibronic energies, providing a comprehensive picture of the AlCl quantum structure. The combination of high resolution spectral data and theory permits the evaluation of spectroscopic constants and associated properties, like equilibrium bond length, with an order of magnitude higher precision. Based on the measured molecular equilibrium constants of the $A^1Pi$ state, we estimate a Franck-Condon factor of the $A^1Pi leftarrow X^1Sigma^+$ of 99.88%, which confirms that AlCl is amenable to laser cooling.
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.
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.
Understanding ultracold collisions involving molecules is of fundamental importance for current experiments, where inelastic collisions typically limit the lifetime of molecular ensembles in optical traps. Here we present a broad study of optically trapped ultracold RbCs molecules in collisions with one another, in reactive collisions with Rb atoms, and in nonreactive collisions with Cs atoms. For experiments with RbCs alone, we show that by modulating the intensity of the optical trap, such that the molecules spend 75% of each modulation cycle in the dark, we partially suppress collisional loss of the molecules. This is evidence for optical excitation of molecule pairs mediated via sticky collisions. We find that the suppression is less effective for molecules not prepared in the spin-stretched hyperfine ground state. This may be due either to longer lifetimes for complexes or to laser-free decay pathways. For atom-molecule mixtures, RbCs+Rb and RbCs+Cs, we demonstrate that the rate of collisional loss of molecules scales linearly with the density of atoms. This indicates that, in both cases, the loss of molecules is rate-limited by two-body atom-molecule processes. For both mixtures, we measure loss rates that are below the thermally averaged universal limit.
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