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1. Photoassociation of ultracold NaLi

   https://doi.org/10.1039/C7CP08480C  

   Rvachov, Timur M.; Son, Hyungmok; Park, Juliana J.; Notz, Pascal M.; Wang, Tout T.; Zwierlein, Martin W.; Ketterle, Wolfgang; Jamison, Alan O. (January 2018, Physical Chemistry Chemical Physics)

   We perform photoassociation spectroscopy in an ultracold 23 Na– 6 Li mixture to study the c 3 Σ + excited triplet molecular potential. We observe 50 vibrational states and their substructure to an accuracy of 20 MHz, and provide line strength data from photoassociation loss measurements. An analysis of the vibrational line positions using near-dissociation expansions and a full potential fit is presented. This is the first observation of the c 3 Σ + potential, as well as photoassociation in the NaLi system. 

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2. Rotational magic conditions for ultracold molecules in the presence of Raman and Rayleigh scattering

   https://doi.org/10.1088/1367-2630/ad56bf  

   Kotochigova, Svetlana; Guan, Qingze; Tiesinga, Eite; Scarola, Vito; DeMarco, Brian; Gadway, Bryce (June 2024, New Journal of Physics)

   Abstract Molecules have vibrational, rotational, spin-orbit and hyperfine degrees of freedom or quantum states, each of which responds in a unique fashion to external electromagnetic radiation. The control over superpositions of these quantum states is key to coherent manipulation of molecules. For example, the better the coherence time the longer quantum simulations can last. The important quantity for controlling an ultracold molecule with laser light is its complex-valued molecular dynamic polarizability. Its real part determines the tweezer or trapping potential as felt by the molecule, while its imaginary part limits the coherence time. Here, our study shows that efficient trapping of a molecule in its vibrational ground state can be achieved by selecting a laser frequency with a detuning on the order of tens of GHz relative to an electric-dipole-forbidden molecular transition. Close proximity to this nearly forbidden transition allows to create a sufficiently deep trapping potential for multiple rotational states without sacrificing coherence times among these states from Raman and Rayleigh scattering. In fact, we demonstrate that magic trapping conditions for multiple rotational states of the ultracold²³Na⁸⁷Rb polar molecule can be created. 

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3. Quantum computation solves a half-century-old enigma: Elusive vibrational states of magnesium dimer found

   https://doi.org/10.1126/sciadv.aay4058  

   Yuwono, Stephen H.; Magoulas, Ilias; Piecuch, Piotr (April 2020, Science Advances)

   The high-lying vibrational states of the magnesium dimer (Mg 2 ), which has been recognized as an important system in studies of ultracold and collisional phenomena, have eluded experimental characterization for half a century. Until now, only the first 14 vibrational states of Mg 2 have been experimentally resolved, although it has been suggested that the ground-state potential may support five additional levels. Here, we present highly accurate ab initio potential energy curves based on state-of-the-art coupled-cluster and full configuration interaction computations for the ground and excited electronic states involved in the experimental investigations of Mg 2 . Our ground-state potential unambiguously confirms the existence of 19 vibrational levels, with ~1 cm −1 root mean square deviation between the calculated rovibrational term values and the available experimental and experimentally derived data. Our computations reproduce the latest laser-induced fluorescence spectrum and provide guidance for the experimental detection of the previously unresolved vibrational levels. 

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4. The nature of supermolecular bonds: Investigating hydrocarbon linked beryllium solvated electron precursors

   https://doi.org/10.1063/5.0089815  

   Jackson, Benjamin A.; Miliordos, Evangelos (May 2022, The Journal of Chemical Physics)

   Beryllium ammonia complexes Be(NH 3 ) 4 are known to bear two diffuse electrons in the periphery of a Be(NH 3 ) 4 2+ skeleton. The replacement of one ammonia with a methyl group forms CH 3 Be(NH 3 ) 3 with one peripheral electron, which is shown to maintain the hydrogenic-type shell model observed for Li(NH 3 ) 4 . Two CH 3 Be(NH 3 ) 3 monomers are together linked by aliphatic chains to form strongly bound beryllium ammonia complexes, (NH 3 ) 3 Be(CH 2 ) n Be(NH 3 ) 3 , n = 1–6, with one electron around each beryllium ammonia center. In the case of a linear carbon chain, this system can be seen as the analog of two hydrogen atoms approaching each other at specific distances (determined by n). We show that the two electrons occupy diffuse s-type orbitals and can couple exactly as in H 2 in either a triplet or singlet state. For long hydrocarbon chains, the singlet is an open-shell singlet nearly degenerate with the triplet spin state, which transforms to a closed-shell singlet for n = 1 imitating the σ-covalent bond of H 2 . The biradical character of the system is analyzed, and the singlet–triplet splitting is estimated as a function of n based on multi-reference calculations. Finally, we consider the case of bent hydrocarbon chains, which allows the closer proximity of the two diffuse electrons for larger chains and the formation of a direct covalent bond between the two diffuse electrons, which happens for two Li(NH 3 ) 4 complexes converting the open-shell to closed-shell singlets. The energy cost for bending the hydrocarbon chain is nearly compensated by the formation of the weak covalent bond rendering bent and linear structures nearly isoenergetic. 

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5. Quantum electronic control on chemical activation of methane by collision with spin–orbit state selected vanadium cation

   https://doi.org/10.1039/D0CP04333H  

   Ng, Cheuk-Yiu; Xu, Yuntao; Chang, Yih-Chung; Wannenmacher, Anna; Parziale, Matthew; Armentrout, P. B. (January 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   By coupling a newly developed quantum-electronic-state-selected supersonically cooled vanadium cation (V + ) beam source with a double quadrupole-double octopole (DQDO) ion–molecule reaction apparatus, we have investigated detailed absolute integral cross sections ( σ 's) for the reactions, V + [a 5 D J ( J = 0, 2), a 5 F J ( J = 1, 2), and a 3 F J ( J = 2, 3)] + CH 4 , covering the center-of-mass collision energy range of E cm = 0.1–10.0 eV. Three product channels, VH + + CH 3 , VCH 2 + + H 2 , and VCH 3 + + H, are unambiguously identified based on E cm -threshold measurements. No J -dependences for the σ curves ( σ versus E cm plots) of individual electronic states are discernible, which may indicate that the spin–orbit coupling is weak and has little effect on chemical reactivity. For all three product channels, the maximum σ values for the triplet a 3 F J state [ σ (a 3 F J )] are found to be more than ten times larger than those for the quintet σ (a 5 D J ) and σ (a 5 F J ) states, showing that a reaction mechanism favoring the conservation of total electron spin. Without performing a detailed theoretical study, we have tentatively interpreted that a weak quintet-to-triplet spin crossing is operative for the activation reaction. The σ (a 5 D 0 , a 5 F 1 , and a 3 F 2) measurements for the VH + , VCH 2 + , and VCH 3 + product ion channels along with accounting of the kinetic energy distribution due to the thermal broadening effect for CH 4 have allowed the determination of the 0 K bond dissociation energies: D 0 (V + –H) = 2.02 (0.05) eV, D 0 (V + –CH 2 ) = 3.40 (0.07) eV, and D 0 (V + –CH 3 ) = 2.07 (0.09) eV. Detailed branching ratios of product ion channels for the titled reaction have also been reported. Excellent simulations of the σ curves obtained previously for V + generated by surface ionization at 1800–2200 K can be achieved by the linear combination of the σ (a 5 D J , a 5 F J , and a 3 F J ) curves weighted by the corresponding Boltzmann populations of the electronic states. In addition to serving as a strong validation of the thermal equilibrium assumption for the populations of the V + electronic states in the hot filament ionization source, the agreement between these results also confirmed that the V + (a 5 D J , a 5 F J , and a 3 F J ) states prepared in this experiment are in single spin–orbit states with 100% purity. 

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