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 fewelectron molecules Invited Speaker: Frederic Merkt Fewelectron molecules are attractive systems for precision spectroscopy because their properties can be calculated with high accuracy by quantumchemical 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 H_{2} and metastable He_{2}. In the case of H_{2}, we determine the ionization energy with a precision (Δν/ν) of 10^{10} from highresolution Rydberg spectra^{4,5 }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 protontoelectron mass ratio would limit the accuracy of otherwise exact calculations. Comparison will be made to recent theoretical results in the context of a morethan100yearlong series of experimental and theoretical determinations of the dissociation energy of H_{2}. In the case of the He_{2}, we use multistage Zeeman deceleration to prepare slow, cold metastable molecules in selected spinrotational components of the metastable a state. We exploit the long transit times of these molecules through microwave and laser fields to measure finestructure intervals in the a state, the Rydberg spectrum of He_{2}, and the energylevel structure of He_{2}^{+}.^{6} 
Wednesday, March 6, 2019 11:51AM  12:03PM 
L24.00002: Precision spectroscopy of molecular hydrogen and its ion through molecular Rydberg states and MQDTassisted extrapolation of Rydberg series Maximilian Beyer, Nicolas Hölsch, Christian Jungen, Frederic Merkt H_{2}^{+} and H_{2} 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: Geminalbased highaccuracy quantum mechanics for fewbody systems Markus Reiher We elaborate on the variational solution of the Schrödinger and Dirac equations of fewbody atomic and molecular systems without relying on the BornOppenheimer 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 laboratoryfixed Cartesian coordinates [2]. For semiclassical relativistic calculations we devised a kineticbalance condition for explicitly correlated basis functions [3]. The resulting form of kinetic balance establishes a relation between all spinor components of an Nfermion system to the nonrelativistic limit, which is in accordance with modern exactdecoupling 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 molecularscale 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 nearfield opens the door for characterization of molecular electronics with nearfield 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 positronatom and positronmolecule 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 Pstate 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 positronatom annihilation and providing experimental evidence for the existence of positronatom 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 electronpositron 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 fiveparticle molecular systems Edit Matyus Solution methods for the fewparticle molecular Schrödinger equation are elaborated relying on both the full electronnucleus Hamiltonian [1] as well as on a perturbative treatment resulting in effective nonadiabatic Hamiltonians for the atomic nuclei [2]. Numerical results are presented for the hydrogen molecule (H_{2}) and for the helium molecular ion (He_{2}^{+}). 
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 alloptical 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 attosecondduration 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 mediumindependent, alloptical method for correcting the phase mismatch is possible. A sequence of counterpropagating pulses locally disrupts the phasematching 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 mesotetrapyridyl 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 5,10,15,20mesotetra(pyridyl)21H,23Hporphyrin (H_{2}TPyP). 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 Qband is clearly developed into many electronic and vibronic transitions, whose the wellknown “four orbital model” finds it difficult to reconcile. Using distinct spectroscopy techniques, we conclude that both Q_{x} and Q_{y}bands comprise, in fact, two quasidegenerated electronic states together with their respective vibronic progressions each. The analysis of the HuangRhys factors and complementary time and polarizationresolved measurements reinforce the need for the proposed Qband multi features remodeling. 
Wednesday, March 6, 2019 1:27PM  1:39PM 
L24.00010: Alloptical measurement of molecular spinning dynamics with highharmonic spectroscopy Peixiang Lu, lixin he, Pengfei Lan We demonstrate an alloptical measurement of the spinning dynamics of molecular rotational wave packet (RWP) with an angular highharmonic spectroscopy. By using a doublepulse excitation scheme, unidirectional rotations (UDR) of the sample molecules are created in experiment. By measuring the timedependent 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 angledependent 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. 

L24.00012: ABSTRACT WITHDRAWN

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