Heterodimers consisting of an alkaline and alkaline-earth metal, such as LiBe are plausible candidates for laser cooling experiments. Once cooled, the unpaired electron on the lithium allows LiBe to be manipulated by both magnetic and electric fields. The electronic structure calculations of You et. al¹ predicted that the 2²Σ⁺ transition is very diagonal, with a 0-0 band Franck-Condon factor of 0.998. Prior to the present study, only the 2²Π - X²Σ⁺ bands (labeled as the C-X system in earlier literature)² had been observed between 19,200 – 20,600 cm⁻¹. We have subsequently extended the spectroscopic characterization of LiBe and recorded the first experimental data for LiBe⁺. Included in this work are the first observations of the 1²Π, 2²Σ⁺, 3²Σ⁺, and 4²Π states of LiBe, and the X¹Σ⁺ ground state of LiBe⁺. Data for the 2²Σ⁺ - X²Σ⁺ transition confirmed the theoretical prediction that LiBe is a promising candidate for laser cooling.

1. You, Y.; Yang, C.L.; Wang, M.S.; Ma, X.G.; Lui, W.W. Theoretical investigations of the laser cooling of a LiBe molecule. Phys. Rev. A. At., Mol., Opt. Phys. 92 (3-A), 032502 (2015).
2. Schlachta, R.; Fischer, L.; Rosmus, P.; Bondybey, V.E. The simplest heteronuclear metal cluster lithium-berllium (LiBe). Chem. Phys. Lett. 170 (5-6), 485-91 (1990).

A measurement of the electron electric dipole moment (eEDM) might be achieved using ytterbium fluoride (YbF) under ultra-cold conditions. One-dimensional laser cooling using the A²Π_1/2 - X²Σ⁺ transition of YbF has been demonstrated, but it appears that laser cooling by means of this transition may be limited by radiative loss of population from the cooling cycle. YbF has low-energy states that arise from the Yb⁺(4f¹³6s)F⁻ configuration (labeled in previous papers as 4f⁻¹ states). Recent theoretical calculations¹ predict that radiative decay from A²Π_1/2 to the 4f⁻¹ states occurs with a branching fraction of approximately 5x10⁻⁴, which may explain why attempts to achieve 3-dimensional cooling have not been successful to date. In the present study we have used dispersed laser induced fluorescence spectroscopy to the observe the lowest energy 4f⁻¹ states. These measurements were carried out using excitation of previously unobserved YbF transitions in the near UV spectral range. The 4f⁻¹ Ω = 1/2 and 3/2 states were found at energies of 8470 and 9070 cm⁻¹ above the ground state. The results are in excellent agreement with the calculations, bolstering confidence in the predicted electric transition dipole moments of Ref. 1.

1. Zhang, C.; Zhang C.; Cheng, L.; Steimle T. C.; Tarbutt M. R., Inner-shell excitation in the YbF molecule and its impact on laser cooling. Accepted for publication, J. Mol. Spec. (2022) and arXiv.org, e-Print Archive, Physics (2022), 1-11

Aluminum monofluoride (AlF) possesses highly favorable properties for laser cooling, both via the A¹Π and a³Π states. Determining efficient pathways between the singlet and the triplet manifold of electronic states will be advantageous for future experiments at ultralow temperatures. The lowest rotational levels of the A¹Π, v=6 and b³Σ⁺, v=5 states of AlF are nearly iso-energetic and interact via spin-orbit coupling. These levels thus have a strongly mixed spin-character and provide a singlet-triplet doorway. We present a hyperfine resolved spectroscopic study of the A¹Π, v=6 // b³Σ⁺, v=5 perturbed system in a jet-cooled, pulsed molecular beam. From a fit to the observed energies of the hyperfine levels, the fine and hyperfine structure parameters of the coupled states, their relative energies as well as the spin-orbit interaction parameter are determined. The radiative lifetimes of selected hyperfine levels are experimentally determined using time-delayed ionization, Lamb dip spectroscopy and accurate measurements of the transition lineshapes. The measured lifetimes range between 2 ns and 200 ns, determined by the degree of singlet-triplet mixing for each level.

Rapid and repeated scattering of laser photons ("optical cycling") underlies many uses of atoms and small molecules for quantum science and measurement. Larger polyatomic molecules are also appealing targets, partly because these species may be decorated with functional groups offering unique scientific opportunities. In this talk, we discuss a large class of aromatic molecules that can be functionalized with an alkaline-earth metal atom to enable optical cycling. We describe the gas-phase production of Ca- and Sr-bearing derivatives of phenyl (Ph) and naphthyl radicals and, using dispersed fluorescence spectroscopy, we show that these molecules contain multiple electronic transitions suitable for optical cycling and laser cooling. We present high-resolution laser excitation spectra for molecules such as fluorinated-CaOPh and SrOPh and compare these to the well-known alkaline-earth monoalkoxides and monoamides. These data inform ongoing work to laser cool and magneto-optically trap a functionalized aromatic molecule.

Buffer gas cooling has emerged as a powerful tool in the study of cold and ultracold molecules. We have demonstrated buffer gas cooling and CW laser absorption spectroscopy on two species: Calcium monohydroxide radical (CaOH) and Phthalocyanine (C₃₂H₁₈N₈). CaOH has gained an increasing attention from astrophysics community due to its expected presence in the atmospheres of cool stars and rocky exoplanets. 3D Magneto-Optical trapping and subsequent sub-Doppler cooling of buffer-gas-cooled CaOH has also recently been reported [1]. Phthalocyanine, on the other hand, is much larger and more complex molecule than CaOH, possessing extremely rich rotational and vibrational structure. For both species, significant rotational cooling has been observed inside the  ∼ 5 K Helium buffer gas cell with estimated rotational temperature of  ∼ 10 K. This is promising, especially for large molecules with spectral congestion, to move molecular population into fewer lines, enhance signals, and drastically simplify spectrum. In this talk, we will present these results and analyses, including the latest data. [1] N. B. Vilas, C. Hallas, L. Anderegg, P. Robichaud, A. Winnicki, D. Mitra, and J. M. Doyle (2021). arXiv:2112.08349

Ethylenediaminetetraacetic acid (EDTA) is a useful model system for studying the ubiquitous divalent ion-carboxylate interactions in protein binding pockets.S. C. Edington, C. R. Baiz, J. Phys. Chem. A 122 (2018) 6585-6592Q. Yuan, X. T. Kong, G. L. Hou, L. Jiang, X. B. Wang, Faraday Discuss. 217 (2019) 383 EDTA can chelate most metal cations by forming up to six bonds with its four carboxyl groups and two nitrogen atoms, resulting in water-soluble complexes that are biologically relevant. Here, we present cryogenic gas-phase infrared spectra of a series of transition metal-EDTA complexes of the form [M(II)·EDTA]²⁻ and assign spectral features using density functional theory calculations. The vibrational spectra inform us of the structure of and intermolecular forces in each complex, revealing the binding geometry of the metal ion within the EDTA binding pocket and its response to changes in ionic radius and electron configuration. The positions of carboxylate vibrational bands depend on the identity of the bound metal, displaying a clear spectral response to changes in binding properties.

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S. C. Edington, C. R. Baiz, J. Phys. Chem. A 122 (2018) 6585-6592

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Isoprene (C₅H₈) is a biogenic volatile organic compound (BVOC) found abundantly in our atmosphere. It is produced by plants and reacts in the atmosphere which leads to the production of aerosols and ozone. Previous spectra taken by our group have shown that, at room temperature, the infrared spectrum of isoprene is congested and difficult to assign, in part due to hot bands. We are currently building a supersonic expansion source that will allow us to cool the isoprene sample to a temperature of around 20 - 30 K. Lowering the temperature of the gas will eliminate hot bands and produce much clearer, less congested spectra. This will allow for a better understanding of isoprene’s fundamental properties through spectral analysis. During this talk we will discuss the progress of the experiment and present preliminary spectra if available.

Observation of complex organic molecules containing peptide bonds such as acetamide and propionamide in the interstellar medium raises the prospect of amino acid formation. Reactions of interstellar ice analogs containing acetaldehyde and ammonia were investigated to better understand the reactivity of oxygen-containing organic molecules with ammonia. These ices were submitted to energetic electron irradiation to simulate the effects of secondary electrons generated by galactic cosmic rays. Photoionization mass spectrometry was used to detect reaction products, while four-wave mixing provided tunable vacuum UV light for single photon ionization. Isotopically labeled acetaldehyde was employed to verify the formula of the observed reaction products. Electronic structure calculations at the CCSD(T)/CBS level predicted the adiabatic ionization energy of all plausible isomers. The differences between the ionization energies of the C₂H₅NO reaction products were used to identify the isomers present. The amino radical, NH₂, was found to bind to the acetaldehyde radical at either carbon. This resulted in the formation of 1-aminoacetaldehyde (CH₃C(O)NH₂), better known as acetamide, and 2-aminoacetaldehyde (NH₂CH₂CHO). Furthermore, with sufficient irradiation, high energy tautomers of both 1- and 2-aminoacetaldehyde were found to form. Both 1-aminoethenol (CH₂C(OH)NH₂) and 2-aminoethenol (OHCHCHNH₂) were identified by measurement of their photoionization efficiency spectra.

c0pt Figure Electron transfer reactions are among the most elementary chemical reactions, which play a fundamental role in organic synthesis, electrochemical processes, and biochemical reactions. In our study, we used sodium as a source of electrons and probed the formation of benzophenone radical anion 2 in an argon and low density amorphous (LDA) water ice matrices using matrix isolation technique. In solid argon, mixture of sodium vapors and benzophenone 1 was co-deposited and after irradiating the matrix with the visible light, electron transfer takes place from sodium to 1 under the formation of radical anion 2. In LDA water ice, hydrated electrons are produced after co-deposition of water with sodium. The hydrated electrons react with benzophenone without photochemical activation and resulted in radical anion 2. However, the photoexcitation of radical anion 2 yielded back benzophenone 1 after losing an electron to the matrix. Reference: [1] A. Somani, W. Sander, J. P. Org. Chem. 2022, e4335.