Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session L24: Precision spectroscopy of molecules: status and perspectivesFocus
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Sponsoring Units: DAMOP Chair: Sergiy Bubin, Nazarbayev University Room: BCEC 159 |
Wednesday, March 6, 2019 11:15AM - 11:51AM |
L24.00001: Precision spectroscopy in few-electron molecules Invited Speaker: Frederic Merkt Few-electron molecules are attractive systems for precision spectroscopy because their properties can be calculated with high accuracy by quantum-chemical methods.1,2,3 The measurements serve to test theoretical predictions, ideally at the level where their accuracy is limited by the uncertainties of the fundamental constants or by unrecognized physical effects. We report on precision measurements of energy intervals in cold samples of H2 and metastable He2. In the case of H2, we determine the ionization energy with a precision (Δν/ν) of 10-10 from high-resolution Rydberg spectra4,5 and derive the dissociation energy with an accuracy of 350 kHz, approaching the level where the size of the proton and the uncertainty in the proton-to-electron mass ratio would limit the accuracy of otherwise exact calculations. Comparison will be made to recent theoretical results in the context of a more-than-100-year-long series of experimental and theoretical determinations of the dissociation energy of H2. In the case of the He2, we use multistage Zeeman deceleration to prepare slow, cold metastable molecules in selected spin-rotational components of the metastable a state. We exploit the long transit times of these molecules through microwave and laser fields to measure fine-structure intervals in the a state, the Rydberg spectrum of He2, and the energy-level structure of He2+.6 |
Wednesday, March 6, 2019 11:51AM - 12:03PM |
L24.00002: Precision spectroscopy of molecular hydrogen and its ion through molecular Rydberg states and MQDT-assisted extrapolation of Rydberg series Maximilian Beyer, Nicolas Hölsch, Christian Jungen, Frederic Merkt H2+ and H2 are the simplest of all ionic and neutral molecules and as such important systems for the development of molecular quantum mechanics. |
Wednesday, March 6, 2019 12:03PM - 12:15PM |
L24.00003: Geminal-based high-accuracy quantum mechanics for few-body systems Markus Reiher We elaborate on the variational solution of the Schrödinger and Dirac equations of few-body atomic and molecular systems without relying on the Born-Oppenheimer paradigm [1]. The wavefunction is expanded in terms of parameterized explicitly correlated Gaussians with polynomial prefactors. We developed a simple strategy for the elimination of the translational kinetic energy of the total energy carried out in laboratory-fixed Cartesian coordinates [2]. For semi-classical relativistic calculations we devised a kinetic-balance condition for explicitly correlated basis functions [3]. The resulting form of kinetic balance establishes a relation between all spinor components of an N-fermion system to the non-relativistic limit, which is in accordance with modern exact-decoupling methods. In my talk, I will discuss these developments in the light of spectroscopic results. |
Wednesday, March 6, 2019 12:15PM - 12:27PM |
L24.00004: Optical angular momentum induced molecular switching Hai Bi, Eric Mazur Molecular electronics is a promising route for downscaling electronic devices since organic molecules can play a role in reconfigurable logic operations. The organic molecule can also strongly interact with optical fields provided that the fields are highly concentrated, for instance by the presence of plasmonic nanostructures. Simultaneously, the plasmonic nanostructures have been demonstrated recently the ability to produce localized angular momentum (LAM), which could further be coupled to a molecular device. By optically transferring angular momentum to a molecular junction, we demonstrate different logic operations. These molecular-scale operations result from the interaction of conducting molecular junction and the plasmonically enhanced electromagnetic field near the tip of the junction. Importantly, this novel investigation of the LAM in the near-field opens the door for characterization of molecular electronics with near-field optical methods. |
Wednesday, March 6, 2019 12:27PM - 12:39PM |
L24.00005: Positronic beryllium: accurate energies and leading relativistic corrections in the ground and lowest excited states Istvan Hornyak, Sergiy Bubin One of the long standing questions of positron physics and chemistry is the existence of electronically stable positron-atom and positron-molecule complexes. From the theoretical and computational viewpoint, reliable identification of states, especially metastable ones, in which a positron can be attached to an atom, is challenging due to very weak binding energies and nontrivial structure of the complexes. A few years ago we predicted the stability against dissociation of an excited P-state of Be. The fact that both the ground and excited states are stable against dissociation in conjunction with their notably different lifetimes opens up an interesting possibility of measuring resonant positron-atom annihilation and providing experimental evidence for the existence of positron-atom complexes. In this work we have undertaken another, more comprehensive study of this system. We have performed considerably more accurate calculations of the binding energies and other relevant properties, such as the electron-positron annihilation rates. In particular, we have computed the leading relativistic corrections and show how they change the tiny binding energies of the ground and first excited states of the e+-Be complex. |
Wednesday, March 6, 2019 12:39PM - 12:51PM |
L24.00006: Precision calculations for four- and five-particle molecular systems Edit Matyus Solution methods for the few-particle molecular Schrödinger equation are elaborated relying on both the full electron-nucleus Hamiltonian [1] as well as on a perturbative treatment resulting in effective non-adiabatic Hamiltonians for the atomic nuclei [2]. Numerical results are presented for the hydrogen molecule (H2) and for the helium molecular ion (He2+). |
Wednesday, March 6, 2019 12:51PM - 1:03PM |
L24.00007: Long Baseline Molecular Interferometry Yaakov Fein, Stefan Gerlich, Philipp Geyer, Filip Kialka, Lukas Mairhofer, Klaus Hornberger, Markus Arndt Interferometry of massive particles can be used to rule out modifications to quantum mechanics [1], test the equivalence principle [2], and measure molecular properties [3]. |
Wednesday, March 6, 2019 1:03PM - 1:15PM |
L24.00008: Counterpropagating light as a means for all-optical phase matching Amy Lytle, Eric Dyke, Etienne Gagnon Frequency conversion through nonlinear optical processes is the core technology behind a new generation of powerful tools, including tunable optical parametric oscillators for spectroscopy and attosecond-duration pulses for studying electronic processes in atoms. Conversion efficiency is often the limiting factor in the power of such sources, due to chromatic dispersion of the nonlinear medium. The phase mismatch is typically compensated by exploiting birefringence or constructing layered media, but these are limited to nonlinear materials amenable to this type of engineering. Recently, it has been shown that a medium-independent, all-optical method for correcting the phase mismatch is possible. A sequence of counterpropagating pulses locally disrupts the phase-matching conditions on a microscopic level. We show how this microscopic disruption is possible in second harmonic generation and test our current theoretical understanding by comparing experimental observations to a numerical model. We also describe the remaining engineering challenges to implementing the use of counterpropagating light for phase matching and other precision optical measurements. |
Wednesday, March 6, 2019 1:15PM - 1:27PM |
L24.00009: Novel insights on the vibronic transitions in free base meso-tetrapyridyl porphyrin Jefferson Marcio Sanches Lopes, Keshav Sharma, Renato Neiva Sampaio, Alzir Azevedo Batista, Amando Siuiti Ito, Antonio Eduardo da Hora Machado, Paulo T Araujo, Newton M Barbosa Neto We present novel results on the free base 5,10,15,20-meso-tetra(pyridyl)-21H,23H-porphyrin (H2TPyP). This molecule presents complex electronic and vibrational properties and in spite of the vast literature reporting the transitions observed in its absorption and fluorescence spectra, a more accurate interpretation has been kept elusive. In particular, we show that the molecule’s Q-band is clearly developed into many electronic and vibronic transitions, whose the well-known “four orbital model” finds it difficult to reconcile. Using distinct spectroscopy techniques, we conclude that both Qx- and Qy-bands comprise, in fact, two quasi-degenerated electronic states together with their respective vibronic progressions each. The analysis of the Huang-Rhys factors and complementary time- and polarization-resolved measurements reinforce the need for the proposed Q-band multi features remodeling. |
Wednesday, March 6, 2019 1:27PM - 1:39PM |
L24.00010: All-optical measurement of molecular spinning dynamics with high-harmonic spectroscopy Peixiang Lu, lixin he, Pengfei Lan We demonstrate an all-optical measurement of the spinning dynamics of molecular rotational wave packet (RWP) with an angular high-harmonic spectroscopy. By using a double-pulse excitation scheme, unidirectional rotations (UDR) of the sample molecules are created in experiment. By measuring the time-dependent angular distributions (ADs) of high harmonic generation (HHG), the spatiotemporal evolution of molecular RWP is intuitively visualized. The harmonic ADs also reveal the electronic structure of the sample molecules. Moreover, due to the correlation of HHG and molecular UDR, HHG from the spinning molecules shows obvious nonadiabatic frequency shift at the rotation revivals. The spinning dynamics of molecular RWP can also be revealed from the angle-dependent frequency shift of HHG. |
Wednesday, March 6, 2019 1:39PM - 1:51PM |
L24.00011: Electronic and Vibrational Anisotropy in Molecular Wavepacket Dynamics Varun Makhija, Albert Stolow Resonant excitation of an isolated molecule typically results in an anistropic distribution of molecular axes in the excited state - alignment or orientation of the molecules in the laborotory frame. Femto- or attosecond laser pulses with broad enough bandwidths can potentially excite several electronic and vibrational states in a molecule. By appropritately coupling the angular momentum of these states, we find that an evolving anisotrpy (alignment or orientation) develops in the electronic and vibrational probabilty distributions, in adition to axis alignment. The evolution of the electronic and vibrational alignment is synchronized with vibronic dynamics occuring in the molecular frame, and can be orders of magnitude faster than molecular rotation. This anisotropy can in princiapal be measured by time and angle resolved scattering. A measurement of the evolving electronic anisotropy in resonantly excited ammonia by time and angle resolved photoelectron spectroscopy confirms the theoretical analyasis. |
Wednesday, March 6, 2019 1:51PM - 2:03PM |
L24.00012: ABSTRACT WITHDRAWN
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