We use narrow-band laser excitation of Yb atoms to substantially enhance the brightness of a cold beam of YbOH, a polyatomic molecule with high sensitivity to physics beyond the standard model (BSM). By exciting atomic Yb to the metastable 3 P 1 state in a cryogenic environment, we significantly increase the chemical reaction cross-section for collisions of Yb with reactants. We characterize the dependence of the enhancement on the properties of the laser light, and study the final state distribution of the YbOH products. The resulting bright, cold YbOH beam can be used to increase the statistical sensitivity in searches for new physics utilizing YbOH, such as electron electric dipole moment and nuclear magnetic quadrupole moment experiments. We also perform new quantum chemical calculations that confirm the enhanced reactivity observed in our experiment and compare reaction pathways of Yb( 3 P) with the reactants H 2 O and H 2 O 2 . More generally, our work presents a broad approach for improving experiments that use cryogenic molecular beams for laser cooling and precision measurement searches of BSM physics.

The pure rotational spectrum of YbOH has been recorded and analyzed to produce fine and magnetic hyperfine parameters for the 2 (0,0,0) X   state. These parameters are compared with those determined from the optical study [Melville and Coxon, J. Chem. Phys. 115, 6974-6978 (2001)] and with the values for YbF [Dickinson et al. 115, 6979-6989 (2001)]. The results support the existence of an unobserved perturbing state near the ̃2 Π 1/2 state, similar to that previously found in YbF. The precisely determined parameters lay the foundation for laser cooling YbOH, which will aid in the search for new physics beyond the standard model. Introduction Recently, it has been proposed [1] that the linear triatomic molecule YbOH may be a sensitive venue for investigating T-violating physics beyond the standard model (BSM), such as the electron electric dipole moment (EDM) and nuclear magnetic quadrupole moment (MQM) via the heavy Yb atom. When compared to the diatomic molecules currently used in BSM searches, the additional degrees of freedom offered by YbOH provide several advantages. Specifically, YbOH has the coexistence of an electronic structure amenable to laser cooling, and closely spaced opposite parity states useful for systematic error rejection[1], which are not simultaneously offered by diatomic systems suitable for EDM and MQM searches. A precision measurement with laser cooled and trapped YbOH could extend coherence times (the current limitation of molecular beam BSM searches [2-4]) by orders of magnitude, ultimately probing T-violating BSM physics at the PeV scale[1]. The analogous study of laser cooled YbF has been actively pursued for some time [2, 3, 5, 6]. YbOH offers several advantages compared to YbF. First, the metastable (0,1,0) bending mode of YbOH contains closely spaced states of opposite parity, which enables full

The odd isotopologues of ytterbium monohydroxide, 171,173 YbOH, have been identified as promising molecules in which to measure parity (P) and time reversal (T) violating physics. Here we characterize the 22 1/2 (0,0,0) (0,0,0) AX +  −  band near 577 nm for these odd isotopologues. Both laser-induced fluorescence (LIF) excitation spectra of a supersonic molecular beam sample and absorption spectra of a cryogenic buffer-gas cooled sample were recorded. Additionally, a novel spectroscopic technique based on laser-enhanced chemical reactions is demonstrated and utilized in the absorption measurements. This technique is especially powerful for disentangling congested spectra. An effective Hamiltonian model is used to extract the fine and hyperfine parameters for the 2 1/2 (0,0,0) A  and 2 (0,0,0) X +  states. A comparison of the determined 2 (0,0,0) X +  hyperfine parameters with recently predicted values (M. Denis, et al.,

Increased background pressure in vacuum chamber test facilities as compared to on-orbit operation has been shown to influence the operation of electric propulsion devices such as Hall thrusters. This study aims to elucidate the impact of pressure on the ionization and acceleration mechanisms in a stationary plasma thruster, model SPT-100 Hall thruster, using time-averaged and time-resolved laser-induced fluorescence velocimetry. The results are compared for the thruster operating at an applied 300 V (∼4.25 A), with vacuum facility background pressures ranging from 1.7 × 10 −5 to 8.0 × 10 −5 torr. Time-averaged measurements reveal that, in general, an upstream shift in the position of the ionization and acceleration regions occurs as the facility pressure is increased above the nominal 1.7 × 10 −5 torr. Time-resolved measurements, implemented using a sample-hold scheme with 1 μs resolution, emphasize that similar acceleration profiles are present within the Hall thruster discharge channel regardless of background pressure. Measurements taken at 3.5 × 10 −5 torr, where the facility background neutral density is similar to the neutral density emitted from the thruster, unexpectedly show increased ion acceleration over the next highest pressure condition at 5.0 × 10 −5 torr. These results indicate a not-yet well defined balance of the impacts of neutral ingestion, classical and turbulent electron transport on thruster operation, and that the ratio of the background to thruster neutral density is a more relevant benchmark than background pressure alone when evaluating Hall thruster operation.

Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic X 2Σ+(010) state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the X 2Σ+(010) state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of 174YbOH using high-resolution optical spectroscopy on the nominally forbidden X 2Σ+(010) → Α 2Π1/2(000) transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the X 2Σ+(010) state, and accurately model the state's structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the X 2Σ+(010) state and fit the molecule-frame dipole moment to D mol = 2.16(1) D and the effective electron g-factor to gS = 2.07(2). Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin-orbit and vibronic perturbations in the excited Α 2Π1/2(000) state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.