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International Symposium on Molecular Spectroscopy (ISMS)

EXTENSIVE HIGH-RESOLUTION PHOTOASSOCIATION SPECTRA AND PERTURBATION ANALYSIS OF 2(0_) LONG-RANGE STATE OF ULTRACOLD RbCs MOLECULES

Jinjun Liu, Chuanliang Li, Yanting Zhao, Zhonghua Ji, Dianqiang Su

Published Jun 18, 2019• 0 citations
Publisher

Abstract

We report high-resolution photoassociation (PA) spectra of RbCs in the 2(0 -) long-range state.Transitions to more than fifty vibrational levels were recorded with the largest binding energy being 507.5 cm -1 .By fitting the experimental transition frequencies to the improved LeRoy-Bernstein formula, the C 6 coefficient for the potential energy curve of the 2(0 -) state was determined to be -1509±97 a.u.. Perturbation-induced energy level shift and state mixing of the longrange 2(0 -) and 3(1) states have been analyzed using an effective Hamiltonian that may be applied to mixing between other excited states of RbCs, as well as other heteronuclear diatomic molecules.Experimentally observed PA transitions to the v = 190 vibrational level of the 2(0 -) state and a vibrational perturbing level in the 3(1) state have been fit using the effective Hamiltonian, which provides the accurate value of the perturbation coefficient β 0 .The experimentally determined rovibronic structure and the deperturbation analysis provide critical information for the search of new schemes for efficient production of ultracold RbCs molecules in the ground state.

DOI
10.15278/isms.2019.te01

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We report high-resolution photoassociation (PA) spectra of RbCs in the 2(0 -) long-range state.Transitions to more than fifty vibrational levels were recorded with the largest binding energy being 507.5 cm -1 .By fitting the experimental transition frequencies to the improved LeRoy-Bernstein formula, the C 6 coefficient for the potential energy curve of the 2(0 -) state was determined to be -1509±97 a.u.. Perturbation-induced energy level shift and state mixing of the longrange 2(0 -) and 3(1) states have been analyzed using an effective Hamiltonian that may be applied to mixing between other excited states of RbCs, as well as other heteronuclear diatomic molecules.Experimentally observed PA transitions to the v = 190 vibrational level of the 2(0 -) state and a vibrational perturbing level in the 3(1) state have been fit using the effective Hamiltonian, which provides the accurate value of the perturbation coefficient β 0 .The experimentally determined rovibronic structure and the deperturbation analysis provide critical information for the search of new schemes for efficient production of ultracold RbCs molecules in the ground state.
We report high-resolution photoassociation (PA) spectra of RbCs in the $2({0}^{\ensuremath{-}})$ long-range state. Transitions to more than 50 vibrational levels were recorded with the largest binding energy being 507.5 ${\mathrm{cm}}^{\ensuremath{-}1}$. By fitting the experimental transition frequencies to the improved LeRoy-Bernstein formula, the C6{C}_{6}C6​ coefficient for the potential energy curve of the $2({0}^{\ensuremath{-}})$ state was determined to be $\ensuremath{-}1509\ifmmode\pm\else\textpm\fi{}97$ a.u.. Perturbation-induced energy level shift and state mixing of the long-range $2({0}^{\ensuremath{-}})$ and 3(1) states have been analyzed using an effective Hamiltonian that may be applied to mixing between other excited states of RbCs, as well as other heteronuclear diatomic molecules. Experimentally observed PA transitions to the $\ensuremath{\nu}=190$ vibrational level of the $2({0}^{\ensuremath{-}})$ state and a vibrational perturbing level in the 3(1) state have been fit using the effective Hamiltonian, which provides the accurate value of the perturbation coefficient ${\ensuremath{\beta}}_{0}$. The experimentally determined rovibronic structure and the deperturbation analysis provide critical information for the search of new schemes for efficient production of ultracold RbCs molecules in the ground state.
We present high resolution photoassociation spectroscopy of RbCs molecules in (2)0(+) long-range state below the Rb(5S1/2) + Cs(6P1/2) asymptote and derive the corresponding C6 coefficient, which is used to revise the potential energy curves. The excited state molecules are produced in a dual-species dark spontaneous force optical trap and detected by ionizing ground state molecules after spontaneous decay, using a high sensitive time-of-flight mass spectrum. With the help of resonance-enhanced two-photon ionization technique, we obtain considerable high resolution photoassociation spectrum with rovibrational states, some of which have never been observed before. By applying the LeRoy-Bernstein method, we assign the vibrational quantum numbers and deduce C6 coefficient, which agrees with the theoretical value of A(1)Σ(+) state correlated to Rb(5S1/2) + Cs(6P1/2) asymptote. The obtained C6 coefficient is used to revise the long-range potential energy curve for (2)0(+) state, which possesses unique A - b mixing characteristic and can be a good candidate for the production of absolutely ground state molecule.
We investigate the possibility of forming deeply bound ultracold RbCs molecules by a two-color photoassociation experiment. We compare the results with those for Rb 2 in order to understand the characteristic differences between heteronuclear and homonuclear molecules. The major differences arise from the different long-range potential for excited states. Ultracold 85 Rb and 133 Cs atoms colliding on the X 1 Σ + potential curve are initially photoassociated to form excited RbCs molecules in the region below the Rb(5S)+Cs(6P 1/2 ) asymptote. We explore the nature of the Ω=0 + levels in this region, which have mixed A 1 Σ + and b 3 Π character. We then study the quantum dynamics of RbCs by a time-dependent wavepacket (TDWP) approach. A wavepacket is formed by exciting a few vibronic levels and is allowed to propagate on the coupled electronic potential energy curves. We calculate the time dependence of the overlap between the wavepacket and ground-state vibrational levels. For a detuning of 7.5 cm −1 from the atomic line, the wavepacket for RbCs reaches the short-range region in about 13 ps, which is significantly faster than for the homonuclear Rb 2 system; this is mostly because of the absence of an R −3 long-range tail in the excited-state potential curves for heteronuclear systems. We give a simple semiclassical formula that relates the time taken to the long-range potential parameters. For RbCs, in contrast to Rb 2 , the excited-state wavepacket shows a substantial peak in singlet density near the inner turning point, and this produces a significant probability of de-excitation to form ground-state molecules bound by up to 1500 cm −1 . The short-range peak depends strongly on non-adiabatic coupling and is reduced if the strength of the spin–orbit coupling is increased. Our analysis of the role of spin–orbit coupling concerns the character of the mixed states in general and is important for both photoassociation and stimulated Raman de-excitation.
We have performed high precision photoassociation spectroscopy of ultracold cesium gas. Using trap-loss fluorescence detection and controlling the background cesium pressure we were able to photoassociate atoms into excited states of ultracold molecules with large detunings up to 56 cm(-1) below the Cs(6S(1/2)) + Cs(6P(1/2)) atomic asymptote. Vibrational progressions are assigned to 0(g)(-), 0(u)(+), and 1(g) long-range states. By fitting the spectral data to the LeRoy-Bernstein expression, the effective coefficients of the leading long-range interactions and the vibrational quantum number at dissociation are obtained. In addition we have observed spectral perturbations between states of the same symmetry belonging to different asymptotes (6P(1/2) and 6P(3/2)). The perturbations are manifested through irregular vibrational level spacings and are especially pronounced in the 0(u)(+) symmetry. Many observed rotational levels indicate d- and higher partial wave contributions to the photoassociation cross section in the presence of trapping laser light, while spectral regions with only weak features suggest nodes in the lower state wave functions corresponding to the two ground state atoms asymptote.
Ultracold polar RbCs molecules are produced via photoassociation in a dual dark-SPOT magneto-optical trap, in which ultracold rubidium and cesium atoms with high densities are formed by laser cooling and trapping. The a3∑+ triplet metastable state ultracold RbCs molecules with 104/s production rate are detected using resonance-enhanced two-photon ionization. The ultra-high resolution rovibrational spectra of (2)0+, (3)0- and (2)0- rovibrational states are observed by scanning the photoassociation laser frequency. The rotational constants of (2)0+, (3)0- and (2)0- vibrational states are 0.00349 cm-1, 0.00649 cm-1 and 0.00372 cm-1 by fitting respectively.
Photoassociation spectroscopy with high resolution for 0u+(6P3/2) long-range state of ultracold cesium molecules has been measured experimentally using the modulated trap loss fluorescence spectroscopy technology. The spectral range has been extended over 60 cm-1 below the 6S1/2 + 6P3/2 dissociation limit as compared with other groups. twenty-five new observations of the Cs2 0u+ in long-range state are reported. The vibrational binding energies of these states are analyzed by using the LeRoy-Bernstein formula. The long-range parameter C3 in molecular 0u+(6P3/2) state is derived for 16.1030.010, and the corresponding molecular potential curve is depicted.