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 C₆ 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 long-range 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 β₀. 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 demonstrate methods for precision spectroscopy and coherent quantum state manipulation of a molecular ion, based on quantum-logic spectroscopy [1-3]. In thermal equilibrium with room temperature blackbody radiation, the electronic and vibrational degrees of freedom of the proof-of-principle CaH⁺ molecule are in their ground states. We laser cool the coupled translational motion of a co-trapped Ca⁺ atom and the molecule to near its ground state [4]. Subsequently, we coherently drive rotational Raman transitions using two beams derived from a single frequency laser that is far off-resonance from any molecular transition. Information regarding the molecular states is transferred to the atomic ion using the coupled harmonic motion as an information bus [1-3] and read out via state-dependent fluorescence detection without disturbing the molecular state. In this way, we initialize the molecular ion in a pure quantum state in a probabilistic but heralded fashion [3]. Following preparation, we can drive further rotational transitions up to the THz range with two beams derived from a single, far-off-resonant frequency comb [5, 6]. The final states of the transitions are detected, enabling unambiguous assignment of the observed signals to the corresponding transitions. For CaH⁺, we have measured the frequency of THz rotational transitions with sub-kHz resolution, and improvement to the sub-Hz level seems feasible [7]. This protocol can be extended to investigate coherent rotational-vibrational transitions of a large class of diatomic and polyatomic molecules in the optical and infrared domains. [1] P. O. Schmidt et al., Science 309, 749 (2005). [2] F. Wolf et al., Nature 530, 457 (2016). [3] C. W. Chou et al., Nature 545, 203 (2017). [4] M. D. Barrett et al., Phys. Rev. A 68, 042302 (2003). [5] D. Leibfried, New J. Phys. 14, 023029 (2012). [6] S. Ding and D. N. Matsukevich, New J. Phys. 14, 023028 (2012). [7] A. Bartels et al., Opt. Lett. 29, 1081 (2004).

Precision spectroscopy of molecules in the mid-infrared region where the fundamental bands are located is of great interest in fundamental physics. In order to achieve a high accuracy, one can measure the spectroscopy in the Lamb-dip zone with sub-Doppler resolution, where further reduction of the laser linewidth and transit-time broadening is perspective. Here we report a new method to reduce the mid-infrared laser linewidth of an optical parametric oscillator (OPO) by locking the pump and idle lights to a frequency comb, resulting in a narrow linewidth and good long-term stability of the signal laser. In this way, we demonstrate that the measured Lamb dip linewidth can be as narrow as tens of kHz and the transition frequency can be determined to an accuracy of a few kHz.

Since the pioneering work of Miescher in the 1960s, the Rydberg states of nitric oxide have held the attention of spectroscopists due to the prototypical energy level structure and rich non-radiative dynamics, which have, in turn, confirmed and challenged existing theory. This work describes a new approach to investigate the relatively underexplored regime of high orbital angular momentum (l) Rydberg states via chirped-pulse Fourier transform millimeter-wave (CP-FTmmW) spectroscopy. We have prepared high-n (n ≥ 27), high-l (l ≥ 4) Rydberg states of NO by a triple resonance laser excitation through the low-lying 4f state, followed by mmW excitation. The mmW field polarizes Rydberg-Rydberg transitions within the bandwidth of our spectrometer (220-330 GHz) and the free induction decay is phase-coherently detected and digitized on a fast oscilloscope. The observed transitions are interpreted in the framework of a long-range electrostatic model for the Rydberg energy level structure, resulting in improved determination of the electric structure (multipole moments, polarizability) of the NO⁺ ion-core. In addition, we will discuss the role of electric fields, hyperfine structure, and non-radiative decay mechanisms – predissociation and autoionization – on the observed mmW spectra.

Spectroscopic and theoretical study of extreme coordinated metal carbonyl complexes has been a subject of intensive studies.^a M(CO)_n⁺ (M = Ti, Zr, Hf) ions were produced by ablating a metal target in a pulse of CO seeded helium, and further studied by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching region. Ti(CO)₆⁺ is formed as dominant species in the mass spectrum, while M(CO)_6,7,8⁺ ions are of the most abundant species in the mass spectra for zirconium and hafnium. The infrared spectra of M(CO)₆⁺ (M = Ti, Zr, Hf) show good agreement with previous reports.^b M(CO)₇⁺ (M = Zr, Hf) ions only dissociate under focused laser irradiation and have one broad band, indicating strongly coordinated complexes. M(CO)₈⁺ (M = Zr, Hf) complexes can fragment by one CO molecule in unfocused light, and each exhibits an infrared band centered at 2084 cm⁻¹(Zr) and 2072 cm⁻¹(Hf). Theoretical calculations indicate that the M(CO)₇⁺ (M = Zr, Hf) complexes are at doublet ground states with C_2v symmetry. The M(CO)₈⁺ (M = Zr, Hf) complexes are identified as 19-electron octacarbonyls. Each of them has D₄ symmetry (distorted cubic geometry) and a doublet ground state. The results extend the knowledge of extreme coordinated carbonyl complexes to Group 4 metals, and provide insights into the ion growth mechanisms in the gas phase.

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Footnotes:

^aZhou, M. F.; Frenking, G. Angew. Chem. Int. Ed. 2018, 57(21), 6236-6241; Science, 2018, 361(6405), 912-916. ^bDuncan, M. A. J. Phys. Chem. A, 2013, 117(46), 11695–11703.

The hydroxyl radical was doped into a helium droplet, and a laser/droplet interaction zone was subjected to a homogeneous 0.425(2) Tesla magnetic field. Mid-infrared Zeeman spectroscopy reveals splittings of the Q(3/2) Λ-doublet transitions that are 21 % larger than those predicted by both degenerate perturbation theory and a variational treatment of the Zeeman effect. This implies simply that the product g_eBΩ_eff is 21 % larger in superfluid helium than in the gas-phase. Although speculative, it is interesting to consider the results in the context of the Einstein-de Haas effect, in which coupling to droplet phonons induces a renormalization of the electron g factor.J.H. Mentink, M.I. Katsnelson, M. Lemeshko, Quantum many-body dynamics of the Einstein-de Hass effect, Phys. Rev. B, 99, 064428 (2019).html:<hr /><h3>Footnotes: J.H. Mentink, M.I. Katsnelson, M. Lemeshko, Quantum many-body dynamics of the Einstein-de Hass effect, Phys. Rev. B, 99, 064428 (2019).

¹⁷⁴YbF has been used for some time in attempts to determine the electrostatic T,P violating electron electric dipole moment (eEDM). It was recently pointed out [1] that ¹⁷³YbF may be an avenue for determining an EDM induced by the magnetic quadrupole moment (MQM). As in the eEDM case, here the molecular properties of ¹⁷³YbF are experimentally advantageous. We report a detailed analysis of the fine and hyperfine structure in the X²Σ⁺ state from a combined analysis of rotational and optical transitions. Numerous hyperfine components in the N=4 → 5 and N=3 → 4 rotational transitions were recorded using a separated field pump/probe microwave optical double residence technique. Fourier transform microwave spectroscopy was used to record five features of the N=0 → 1 rotational transition. This rotational data was combined with precisely measured (0,0) A²π_1/2 - X²Σ⁺ optical transitions of a cold molecular beam sample. Resulting fine and hyperfine parameters will be discussed and compared with recent theory [2]. The research at Arizona State University was supported by a grant from the Heising Simons Foundation (Grant 2018-0681). 1. V.V. Flambaum, et al., arXiv:1810.02477v2 [hep-ph] (10 Dec 2018) 2. P. Schwerdtfeger, et al., Mol. Phys. 114, 1110 (2016)

Ytterbium monofluoride, YbF, has long been used as a venue in attempts to measure the electron electric dipole moment (eEDM)¹⁻² . In addition to the molecular EDM resulting from the eEDM contribution, the ¹⁷³Yb (16.1%, I=5/2) isotopic form of Yb-containing molecules are also expected to have an EDM caused by an interaction of a nuclear magnetic quadrupole moment (NMQM)³ with the electrons. As pointed out by Kozyryev and Hutzler⁴, the X²Σ⁺(01¹0) level of YbOH is expected to exhibit enhanced sensitivity for EDM measurements, relative to YbF, largely due to the ease of polarization. The degenerate bending vibrational levels of YbOH are poorly characterized⁵. Here we report on high-resolution studies of the molecular beam of the A²Π_1/2- X²Σ⁺ (010-000) and A²Π_1/2- X²Σ⁺ (010-010) transitions of YbOH. In addition, the dispersed fluorescence resulting from the excitation of rotationally resolved branch features has been analyzed to produce fluorescence branching ratios. Implications for planned EDM measurements will be presented. Funded by a grant from the Heising-Simons Foundation. References: 1.Hudson, J. J.; Sauer, B. E.; Tarbutt, M. R.; Hinds, E. A., Phys. Rev. Lett. 2002, 89 (2), 023003/1-023003/4. 2.Tarbutt, M. R.; Sauer, B. E.; Hudson, J. J.; Hinds, E. A., New J. Phys. 2013, 15 (May), 053034/1-053034/17. 3.Lackenby, B. G. C.; Flambaum, V. V., Nucl. Theory 2017, 1-7. 4.Kozyryev, I.; Hutzler, N. R., arXiv.org, e-Print Arch., Phys. 2017, 1-11. 5.Melville, T. C.; Coxon, J. A., J. Chem. Phys. 2001, 115 (15), 6974-6978.

Ytterbium monofluoride, YbF, has long been used as a venue in attempts to measure the electron electric dipole moment (eEDM) Hudson, J. J.; Sauer, B. E.; Tarbutt, M. R.; Hinds, E. A., Measurement of the Electron Electric Dipole Moment Using YbF Molecules. Phys. Rev. Lett. 2002, 89 (2), 023003/1-023003/4.^,Tarbutt, M. R.; Sauer, B. E.; Hudson, J. J.; Hinds, E. A., Design for a fountain of YbF molecules to measure the electron′s electric dipole moment. New J. Phys. 2013, 15 (May), 053034/1−053034/17. As pointed out by Kozyryev and Hutzler Kozyryev, I.; Hutzler, N. R., Precision measurement of time−reversal symmetry violation with laser−cooled polyatomic molecules. arXiv.org, e−Print Arch., Phys. 2017, 1−11. Yb containing symmetric top molecules are expected to exhibit enhanced sensitivity for EDM measurements, relative to YbF. This is largely due to the ease of polarization of the K 1 rotational levels. Here we report on our initial molecular beam studies of the heretofore unknown molecules YbOCH₃ and YbOCD₃. Broad survey scans using two dimensional (excitation vs dispersed fluorescence) spectroscopy in the 600−480 nm range were recorded. An intense band detected near 579 nm is assigned to the origin band of the electronic transition of YbOCH₃. The high−resolution ( Tarbutt, M. R.; Sauer, B. E.; Hudson, J. J.; Hinds, E. A., Design for a fountain of YbF molecules to measure the electron's electric dipole moment. New J. Phys. 2013, 15 (May), 053034/1-053034/17..Kozyryev, I.; Hutzler, N. R., Precision measurement of time-reversal symmetry violation with laser-cooled polyatomic molecules. arXiv.org, e-Print Arch., Phys. 2017, 1-11.,

Theoretical study of ThO and HfF⁺ for the experiments to search for the electron electric dipole moment (eEDM) are reported. The g-factors [1,2], effective electric field in the molecule acting on the eEDM [3], hyperfine structure, Zeeman and Stark effects [3,4,5] (including dynamic) for the eEDM sensitive ³∆₁ states are calculated with high accuracy. Calculations are required for interpretation of the experiments and estimation of systematic effects.

1. A.N. Petrov, L.V. Skripnikov, A.V. Titov, N.R. Hutzler, P.W. Hess, B.R. O'Leary, B. Spaun, D. DeMille, G. Gabrielse, and J.M. Doyle, Phys.Rev.A 89, 062505 (2014)
2. A. N. Petrov, L. V. Skripnikov, and A. V. Titov, Phys. Rev. A 96, 022508 (2017)
3. A.N. Petrov, Phys.Rev.A, 91, 062509 (2015)
4. A. N. Petrov, Phys. Rev. A 95, 062501 (2017)
5. A.N. Petrov, Phys.Rev.A, 97, 052504 (2018)