Session C02: Structure and spectroscopy of atoms and molecules

Live

Four-electron systems are the current testing ground for many advanced theoretical models and also tests of quantum electrodynamics.~ In this talk, we will present our current progress on updated experimental measurements for a variety of energy levels in neutral beryllium-9, compare them to current theoretical predictions, and motivate future theoretical calculations to compare to these experimental results.   

Live

All available experimental data on the resonance lines of Li-like ions have been critically compiled. Systematic errors have been corrected in several sets of old measurements, a few outlying measurements have been excluded, and weighted means of all remaining experimental values have been found. Differences of these weighted experimental means from two sets of advanced quantum-mechanical calculations have been fitted with smooth functions of nuclear charge $Z$. From this fitting, accurate recommended data have been derived for all $Z$ between 6 and 92. These recommended data significantly disagree with both theories. While the discrepancies for low $Z$ (\textless 18) and for high $Z$ (\textgreater 70) can be explained by deficiencies in theoretical treatment of inter-electron correlations and nuclear shapes, the discrepancies of a few sigma in the mid-$Z$ range (20--30) are puzzling.   

Live

We will describe our measurement of the ground state tensor polarizability (GSTP) of Cs using laser cooled atoms trapped in optical lattices and discuss our preliminary results. Precision measurement of the Cs GSTP can help test atomic calculations of the hyperfine interactions between nuclear moments and electrons, which are a challenging part of atomic parity-violation calculations. We directly measure the GSTP by driving transitions between magnetic sublevels and measuring the populations in individual magnetic sublevels. We study systematic effects by independently varying electric and magnetic fields and the optical lattice depth. We anticipate at least an order of magnitude improvement in the precision of F$=$4 hyperfine level GSTP measurement and a similar precision in this first ever F$=$3 GSTP measurement.   

Live

Theory of the uranium atom is quite challenging due to a large number of valence electrons, strong mixing between states, strong valence-core interaction and relativistic effects. While energies can be brought in agreement with adjustable parameters, this does not guarantee the correctness of the wavefunctions. Transition probabilities can be used to test the wavefunctions, but their experimental values have significant uncertainty, which arises from uncertainty of density measurements or LTE approximation. Many measurements have substantial disagreement. Hyperfine constants, on the other hand, can be measured with good precision. The configuration-interaction many-body perturbation theory (CI-MBPT) method$^{\mathrm{1}}$ was applied to calculations of hyperfine constants and a good agreement was found with experiment. We also conducted measurements of hyperfine A and B values for the J$=$5 even state (energy 11613.975 cm$^{\mathrm{-1}})$ using atomic beam method$^{\mathrm{2}}$, and found that the measurements are in good agreement with our theory. The results of theoretical calculations and new measurements will be reported. 1. IM Savukov, PM Anisimov, Physical Review A 99 (3), 032507 (2019). 2. V. Lebedev, J.H. Bartlett, and A. Castro, J. Anal. At. Spectrom. 33, 1862-1866 (2018).   

Live

Precise measurements of vibrational transition frequencies in the isotopes of molecular hydrogen can provide a sensitive probe of fundamental physics. Because these transitions can be predicted with high precision using ab-initio theory, comparisons between theory and experiment can be used to test quantum electrodynamics, search for new physics, and determine the proton-electron mass ratio more precisely. We report a measurement of the 0-1 R(0) vibrational transition frequency in deuterium hydride (HD) made using infrared-ultraviolet double resonance spectroscopy in a pulsed supersonic molecular beam. Molecules in the $v=0$, $J=0$ state are excited to $v=1$, $J=1$ using a tunable infrared laser stabilized to an optical frequency comb, and the excitation efficiency is determined using state-selective ionization of the vibrationally excited molecules. Based on the measured infrared spectra, we have determined the transition frequency with an uncertainty of less than 20 kHz ($2\cdot10^{-10}$ fractional uncertainty), which is limited primarily by the residual first-order Doppler shift.   

Live

We constructed an experimental setup for investigating the effect of polarization on the ladder-type Electromagnetically Induced Transparency (EIT) spectra of $^{\mathrm{133}}$Cs atoms at room temperature for the transitions 6$^{\mathrm{2}}$P$_{\mathrm{1/2}}$-6$^{\mathrm{2}}$P$_{\mathrm{3/2}}$-11$^{\mathrm{2}}$S$_{\mathrm{1/2}}$. The whole spectra with additional peaks arisen from Doppler effect are observed. As the relative angle rotates from 0$^{\mathrm{o\thinspace }}$to 90$^{\mathrm{o}}$, the peak height ratio of 44$^{\mathrm{'}}$ 3$^{\mathrm{"}}$ to 44$^{\mathrm{'}}$ 4$^{\mathrm{"}}$ drastically increases from 1:5.3 to 1.4:1 while that of 45$^{\mathrm{'}}$ 4$^{\mathrm{"}}$ to 44$^{\mathrm{'}}$ 4$^{\mathrm{"}}$ slightly increases from 1:1.6 to 1.2:1. A theoretical model built to explain the experimental results with the considerations of optical pumping effect and two-photon transition probability for each Zeeman sublevel, where the optical pumping effect realigns the population of the involving Zeeman sublevels so that the corresponding optical pumping ratio of 44$^{\mathrm{'}}$ 3$^{\mathrm{"}}$/44$^{\mathrm{'}}$ 4$^{\mathrm{"}}$ changes from 0.4 to 0.8 and the corresponding two-photon transition probability goes from 0.23 to 1.9. These two factors contribute to an increase in the ratio of the effective factor which is the product of optical pumping and two-photon transition probability of 44$^{\mathrm{'}}$ 3$^{\mathrm{"}}$/44$^{\mathrm{'}}$ 4$^{\mathrm{"}}$ changes from 0.09 to 1.52. This trend is in correspondence with the peak height ratio change. A similar argument for the 45$^{\mathrm{'}}$ 4$^{\mathrm{"}}$/44$^{\mathrm{'}}$ 4$^{\mathrm{"}}$ peak height ratio is found. The simulated and experimental results show an excellent agreement when taking into account the dephasing rate.   

On Demand

Electroluminescence (EL) spectra were recorded for the first time and the possibility of electrolysis of the formation of the nanoporous structure of aluminum oxide (Al2O3) in chemically pure water with different contents of protium (H) and deuterium (D) isotopes was shown. The similarity of the Al2O3 structure during its formation in aqueous solutions of electrolytes was revealed. It was found that under constant anodizing conditions (temperature 298 K, voltage 1.2 kV and anodizing time 1700 s), the structure of formed Al2O3 differs significantly for protium water (H2O 99.99{\%}) and deuterium water (D2O 99.90{\%}) ) In the first electrolyte, the oxide has a spongy structure with an average pore diameter of 600 nm, and in the second, their average diameter does not exceed 100 nm. The maxima of the spectra of the EL generated during this process are in the short-wavelength region of the visible range and, accordingly, are 455.2 nm for Al2O3 in H2O and 445.9 nm in D2O, which suggests a shift of the maxima by 9.3 nm. In the long-wavelength region (range 611 - 613 nm), this shift is smaller and amounts to 1.6 nm. It was found that the EL brightness of formed Al2O3 in H2O is 1.6 times higher than in D2O.   

Not Participating

Seven-times ionized cerium ion has Sb I-like structure, and 5s$^{\mathrm{2}}$5p$^{\mathrm{3}}$ $^{\mathrm{4}}$S$_{\mathrm{3/2}}$ as the ground state. The 5s$^{\mathrm{2}}$5p$^{\mathrm{3}}$- 5s5p$^{\mathrm{4}}$ transitions transition array was studied using observed cerium spectrum. This spectrum was recorded on a 3-m normal incidence vacuum spectrograph at Antigonish lab (Canada). In this study all the energy levels of the ground configuration was established using the Visual Line-and-Level Identification Program (IDEN2). This analysis was theoretically supported by relativistic (multiconfiguration Dirac-Hartree-Fock) and pseudo relativistic (Hartree-Fock with relativistic correction) method followed by configuration interaction. Along with the energy levels, transition probabilities, oscillator strength and lifetimes were also calculated. The observed levels then optimized with the computer code LOPT.   

Not Participating

Semiclassical simulations are widely used alternative approaches to many-particle systems which have been long-standing challenges for quantum mechanics. Widely known examples include molecular dynamics simulations for proteins and particle-in-cell simulations for plasmas. Strong-field atomic physics is another area where classical simulations play an important role. Many insights about the atomic ionization process, especially double or multiple ionization processes, are obtained with classical simulations. A classical multielectron model atom, however, suffers two problems. The first problem is that the atom is not stable. The second (less known and more subtle) problem is incorrect ionization energies. In this presentation, we propose a method to build stable classical multielectron model atoms with the ionization energies optimized to experimental values. Based on the work of Kirschbaum and Wilets [Phys. Rev. A 21, 834 (1980)], which introduces auxiliary potentials to simulate quantum mechanical effects, we implement a genetic algorithm to optimize the related parameters such that the model atoms yield correct (first few) ionization energies. Ionization-energy optimized model atoms automatically show separated electron shells, consistent to normal expectations. Numerical examples are given to demonstrate the importance of correct ionization energies, as well as new perspectives to double ionization processes.   

Systematic characterization in hydrogen 2S-8D spectroscopy.

We will present progress in measuring the 2S-8D transition in hydrogen using a cryogenic metastable hydrogen beam (approx. 5 K), with a focus on the characterization of key systematics surrounding this measurement.~ In particular, we will present a characterization of the residual Zeeman shifts and measurements of the 2S-12D lineshape, which is used to characterize DC Stark shifts within the apparatus.~ The measurement of the 2S-8D transition in hydrogen can be used to determine the proton charge radius and the Rydberg constant.