Physical Sciences and Mathematics Commons^™

Improving The Efficiency Of Liquid-Hydrogen Simulation Via Event Storage, Jake Kosa

Physics and Astronomy Summer Fellows

We contributed to the analysis of gamma-ray spectroscopy data collected at the Facility for Rare Isotope Beams at Michigan State University by speeding up the UCGretina simulation code, used in the analysis and planning of experiments. Simulating beam-target interactions in a liquid-hydrogen target system is a time intensive task, even when parallelized. In the process of analyzing data, a large number of simulations must be run for different gamma-ray energies, target positions, and lifetimes of excited states. We are addressing the most computationally intensive component of the simulations by adding the ability to simulate a large sample of beam particles …

Quantum Chemistry–Machine Learning Approach For Predicting Properties Of Lewis Acid–Lewis Base Adducts, Hieu Huynh, Thomas J. Kelly, Linh Vu, Tung Hoang, Phuc An Nguyen, Tu C. Le, Emily Jarvis, Hung Phan

Chemistry and Biochemistry Faculty Works

Synthetic design allowing predictive control of charge transfer and other optoelectronic properties of Lewis acid adducts remains elusive. This challenge must be addressed through complementary methods combining experimental with computational insights from first principles. Ab initio calculations for optoelectronic properties can be computationally expensive and less straightforward than those sufficient for simple ground-state properties, especially for adducts of large conjugated molecules and Lewis acids. In this contribution, we show that machine learning (ML) can accurately predict density functional theory (DFT)-calculated charge transfer and even properties associated with excited states of adducts from readily obtained molecular descriptors. Seven ML models, built …

Data From: Chemical Bonding Analysis Of Excited States Using The Adaptive Natural Density Partitioning Method, Alexander I. Boldyrev, Nikolay Tkachenko

Browse all Datasets

A novel approach to chemical bond analysis for excited states has been developed. Using an extended adaptive natural density partitioning method (AdNDP) as implemented in AdNDP 2.0 code, we obtained chemically intuitive bonding patterns for the excited states of H2O, B5+, and C2H4+ molecules. The deformation pathway in the excited states could be easily predicted based on the analysis of the chemical bond pattern. We expect that this new method of chemical bonding analysis would be very helpful for photochemistry, photoelectron spectroscopy, electron spectroscopy and other chemical applications that involved excited states.

Revealing The Hidden Hyperfine Interactions In Ε-Iron, Dimitrios Bessas, Ilya Sergueev, Konstantin Glazyrin, Cornelius Strohm, Ilya Kupenko, Daniel G. Merkel, Gary J. Long, Fernande Grandjean, Aleksandr I. Chumakov, Rudolf Ruffer

Chemistry Faculty Research & Creative Works

Herein, evidence for the long-sought finite hyperfine interaction in the high-pressure hexagonal close-packed ε-iron is gained through synchrotron radiation perturbed angular correlation spectroscopy. This method yields an energy splitting of 3.5(5)neV between the m_Ie= ± 1/2 and m_Ie = ± 3/2 nuclear sublevels of the iron-57 14.412-keV nuclear excited state at 30(1)GPa and room temperature. This energy splitting is related to a nuclear quadrupole hyperfine interaction with an electric field gradient of eq=1.2(2) x 10¹⁶V/cm². However, there is still a possibility that the splitting of the iron-57 nuclear levels is related …

Quench Dynamics Of Finite Bosonic Ensembles In Optical Lattices With Spatially Modulated Interactions, T. Plaßmann, Simeon I. Mistakidis, P. Schmelcher

Physics Faculty Research & Creative Works

The Nonequilibrium Quantum Dynamics Of Few Boson Ensembles Which Experience A Spatially Modulated Interaction Strength And Are Confined In Finite Optical Lattices Is Investigated. We Utilize A Cosinusoidal Spatially Modulated Effective Interaction Strength Which Is Characterized By Its Wavevector, Inhomogeneity Amplitude, Interaction Offset And A Phase. Performing Quenches Either On The Wavevector Or The Phase Of The Interaction Profile An Enhanced Imbalance Of The Interatomic Repulsion Between Distinct Spatial Regions Of The Lattice Is Induced. Following Both Quench Protocols Triggers Various Tunneling Channels And A Rich Excitation Dynamics Consisting Of A Breathing And A Cradle Mode. All Modes Are Shown …

An Experimental And Theoretical Study Of Ã2A"Π–X~2A' Band System Of The Jet-Cooled Hbbr/Dbbr Free Radical, Mohammed Gharaibeh, Dennis J. Clouthier, Riccardo Tarroni

Chemistry Faculty Publications

The electronic spectra of the HBBr and DBBr free radicals have been studied in depth. These species were prepared in a pulsed electric discharge jet using a precursor mixture of BBr₃ vapor and H₂ or D₂ in high pressure argon. Transitions to the electronic excited state of the jet-cooled radicals were probed with laser-induced fluorescence and the ground state energy levels were measured from the single vibronic level emission spectra. HBBr has an extensive band system in the red which involves a linear-bent transition between the two Renner-Teller components of what would be a ²Π state …

Hyperfine Rather Than Spin Splittings Dominate The Fine Structure Of The B 4Σ-–X 4Σ- Bands Of Aic, Dennis J. Clouthier, Aimable Kalume

Chemistry Faculty Publications

Laser-induced fluorescence and wavelength resolved emission spectra of the B ⁴Σ⁻–X ⁴Σ⁻ band system of the gas phase cold aluminum carbide free radical have been obtained using the pulsed discharge jet technique. The radical was produced by electron bombardment of a precursor mixture of trimethylaluminum in high pressure argon. High resolution spectra show that each rotational line of the 0-0 and 1-1 bands of AlC is split into at least three components, with very similar splittings and intensities in both the P- and R-branches. The observed structure was reproduced by assuming b …

Sign Learning Kink-Based (Silk) Quantum Monte Carlo For Molecular Systems, Xiaoyao Ma, Randall W. Hall, Frank Loffler, Karol Kowalski, Kiran Bhaskaran-Nair, Mark Jarrell, Juana Moreno

Collected Faculty and Staff Scholarship

The Sign Learning Kink (SiLK) based Quantum Monte Carlo (QMC) method is used to calculate the ab initioground state energies for multiple geometries of the H₂O, N₂, and F₂ molecules. The method is based on Feynman’s path integral formulation of quantum mechanics and has two stages. The first stage is called the learning stage and reduces the well-known QMC minus sign problem by optimizing the linear combinations of Slater determinants which are used in the second stage, a conventional QMC simulation. The method is tested using different vector spaces and compared to the results of …

Bh2 Revisited: New, Extensive Measurements Of Laser-Induced Fluorescence Transitions And Ab Initio Calculations Of Near-Spectroscopic Accuracy, Fumie X. Sunahori, Mohammed Gharaibeh, Dennis J. Clouthier, Riccardo Tarroni

Chemistry Faculty Publications

The spectroscopy of gas phase BH₂ has not been explored experimentally since the pioneering study of Herzberg and Johns in 1967. In the present work, laser-induced fluorescence (LIF) spectra of the òB₁(Πu)-X̃²A₁ band system of ¹¹BH₂, ¹⁰BH₂, ¹¹BD₂, and ¹⁰BD₂ have been observed for the first time. The free radicals were "synthesized" by an electric discharge through a precursor mixture of 0.5% diborane (B₂H₆ or B₂D₆) in high pressure argon at the exit of …

Collectivity Of 0+ States In 160Gd, S. R. Lesher, C. Casarella, A. Aprahamian, B. P. Crider, R. Ikeyama, I. R. Marsh, Marcus T. Mcellistrem, Erin E. Peters, F. M. Prados-Estévez, M. K. Smith, Z. R. Tully, J. R. Vanhoy, Steven W. Yates

Chemistry Faculty Publications

Excited 0⁺ states in ¹⁶⁰Gd have been examined with the (n,n′γ) reaction at incident neutron energies up to 2.8 MeV. Gamma-ray excitation functions and angular distribution measurements allow the confirmation of the existence of 0⁺ states at 1379.70 keV and 1558.30 keV, but we reject the assignments of additional previously suggested 0⁺ candidates. Limits on the level lifetimes of the observed 0⁺ states permit an evaluation of the collectivity of these states.

The Requisite Electronic Structure Theory To Describe Photoexcited Nonadiabatic Dynamics: Nonadiabatic Derivative Couplings And Diabatic Electronic Couplings, Joseph E. Subotnik, Ethan Alguire, Qi Ou, Brian R. Landry, Shervin Fatehi

Chemistry Faculty Publications and Presentations

Conspectus

Electronically photoexcited dynamics are complicated because there are so many different relaxation pathways: fluorescence, phosphorescence, radiationless decay, electon transfer, etc. In practice, to model photoexcited systems is a very difficult enterprise, requiring accurate and very efficient tools in both electronic structure theory and nonadiabatic chemical dynamics. Moreover, these theoretical tools are not traditional tools. On the one hand, the electronic structure tools involve couplings between electonic states (rather than typical single state energies and gradients). On the other hand, the dynamics tools involve propagating nuclei on multiple potential energy surfaces (rather than the usual ground state dynamics).

In this …

Applied Quantum Chemistry: Spectroscopic Detection And Characterization Of The F2Bs And Cl2Bs Free Radicals In The Gas Phase, Bing Jin, Phillip M. Sheridan, Dennis J. Clouthier

Chemistry Faculty Publications

In this and previous work [D. J. Clouthier, J. Chem. Phys. 141, 244309 (2014)], the spectroscopic signatures of the X₂BY (X = H, halogen, Y = O, S) free radicals have been predicted using high level ab initio theory. The theoretical results have been used to calculate the electronic absorption and single vibronic level (SVL) emission spectra of the radicals under typical jet-cooled conditions. Using these diagnostic predictions, the previously unknown F₂BS and Cl₂BS free radicals have been identified and characterized. The radicals were prepared in a free jet expansion by subjecting precursor …

An Experimental And Theoretical Study Of The Electronic Spectrum Of The Hbcl Free Radical, Mohammed A. Gharaibeh, Ramya Nagarajan, Dennis J. Clouthier, Riccardo Tarroni

Chemistry Faculty Publications

Following our previous discovery of the spectra of the HBX (X = F, Cl, and Br) free radicals [S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)], the òA″Π-X̃²A' band systems of the HBCl and DBCl free radicals have been studied in detail. The radicals have been prepared in a pulsed electric discharge jet using a precursor mixture of BCl₃ and H₂ or D₂ in high pressure argon. Laser-induced fluorescence (LIF) and single vibronic level emission spectra have been recorded to map out the ground …

Rotational Quenching Of H2O By He: Mixed Quantum/Classical Theory And Comparison With Quantum Results, Mikhail V. Ivanov, Marie-Lise Dubernet, Dmitri Babikov

Chemistry Faculty Research and Publications

The mixed quantum/classical theory (MQCT) formulated in the space-fixed reference frame is used to compute quenching cross sections of several rotationally excited states of water molecule by impact of He atom in a broad range of collision energies, and is tested against the full-quantum calculations on the same potential energy surface. In current implementation of MQCT method, there are two major sources of errors: one affects results at energies below 10 cm⁻¹, while the other shows up at energies above 500 cm⁻¹. Namely, when the collision energy E is below the state-to-state transition energy ΔE the …

On Readout Of Vibrational Qubits Using Quantum Beats, Dmytro Shyshlov, Eduardo Berrios, Martin Gruebele, Dmitri Babikov

Chemistry Faculty Research and Publications

Readout of the final states of qubits is a crucial step towards implementing quantum computation in experiment. Although not scalable to large numbers of qubits per molecule, computational studies show that molecular vibrations could provide a significant (factor 2–5 in the literature) increase in the number of qubits compared to two-level systems. In this theoretical work, we explore the process of readout from vibrational qubits in thiophosgene molecule, SCCl₂, using quantum beat oscillations. The quantum beats are measured by first exciting the superposition of the qubit-encoding vibrational states to the electronically excited readout state with variable time-delay pulses. …

Mixed Quantum/Classical Calculations Of Total And Differential Elastic And Rotationally Inelastic Scattering Cross Sections For Light And Heavy Reduced Masses In A Broad Range Of Collision Energies, Alexander Semenov, Dmitri Babikov

Chemistry Faculty Research and Publications

The mixed quantum/classical theory (MQCT) for rotationally inelastic scattering developed recently [A. Semenov and D. Babikov, J. Chem. Phys.139, 174108 (2013)] is benchmarked against the full quantum calculations for two molecular systems: He + H2 and Na + N2. This allows testing new method in the cases of light and reasonably heavy reduced masses, for small and large rotational quanta, in a broad range of collision energies and rotational excitations. The resultant collision cross sections vary through ten-orders of magnitude range of values. Both inelastic and elastic channels are considered, as well as differential (over scattering angle) cross sections. In …

Experimental And Theoretical Cross Sections For Molecular-Frame Electron-Impact Excitation-Ionization Of D₂, Julian C A Lower, Esam S M Ali, Susan M. Bellm, Erich Weigold, Allison L. Harris, Chuangang Ning, Don H. Madison

Physics Faculty Research & Creative Works

We present both experimental and theoretical results for the dissociative ionization of D₂ molecules induced by electron impact. Cross sections are determined in the molecular frame and are fully differential in the energies and emission angles of the dissociation fragments. Transitions are considered from the X¹Σ_g⁺ electronic ground state of D₂ to the 2sσ_g, 2pπ_u and 2pσ_u excited states of D₂⁺. The experimental results are compared to calculations performed within the molecular four-body distorted-wave framework to describe the multicenter nature of the scattering process. The cross sections …

Spectroscopy And Dynamics Of The Predissociated, Quasi-Linear S₂ State Of Chlorocarbene, Chong Tao, Craig A. Richmond, Calvin Mukarakate, Scott H. Kable, George B. Bacskay, Eric C. Brown, Richard Dawes, Phalgun Lolur, Scott A. Reid

Chemistry Faculty Research & Creative Works

In this work, we report on the spectroscopy and dynamics of the quasi-linear S₂ state of chlorocarbene, CHCl, and its deuterated isotopologue using optical-optical double resonance (OODR) spectroscopy through selected rovibronic levels of the S₁ state. This study, which represents the first observation of the S₂ state in CHCl, builds upon our recent examination of the corresponding state in CHF, where pronounced mode specificity was observed in the dynamics, with predissociation rates larger for levels containing bending excitation. In the present work, a total of 14 S₂ state vibrational levels with angular momentum 1 were observed …

Abstract Criteria For Multiple Solutions To Nonlinear Coupled Equations Involving Magnetic Schrodinger Operators, Mattias Enstedt, Michael Melgaard

Articles

We consider a system of nonlinear coupled equations involving magnetic Schrodinger

operators and general potentials. We provide a criteria for the existence of multiple

solutions to these equations. As special cases we get the classical results on

existence of innitely many distinct solutions within Hartree and Hartree-Fock

theory of atoms and molecules subject to an external magnetic fields. We also

extend recent results within this theory, including Coulomb system with a constant

magnetic field, a decreasing magnetic field and a "physically measurable" magnetic field.

Generation Of Coherent Structures After Cosmic Inflation, Marcelo Gleiser, Noah Graham, Nikitas Stamatopoulos

Dartmouth Scholarship

We investigate the nonlinear dynamics of hybrid inflation models, which are characterized by two real scalar fields interacting quadratically. We start by solving numerically the coupled Klein-Gordon equations in static Minkowski spacetime, searching for possible coherent structures. We find long-lived, localized configurations, which we identify as a new kind of oscillon. We demonstrate that these two-field oscillons allow for “excited” states with much longer lifetimes than those found in previous studies of single-field oscillons. We then solve the coupled field equations in an expanding Friedmann-Robertson-Walker spacetime, finding that as the field responsible for inflating the Universe rolls down to oscillate …

Antiaromatic Dianions: Dianions Of Dixanthylidene By Reduction And Attempted Excited-State Deprotonation, Mary Black, Clifford Woodford, Nancy S. Mills

Chemistry Faculty Research

Reduction of dixanthylidene with potassium or lithium resulted in formation of the antiaromatic dianion in high yield. Attempts to form the dianion by excited-state deprotonation of dixanthene with n-butyllithium/TMEDA resulted in formation of the tetraanion from deprotonation ortho to the oxygen. Orientation of the sp3 hydrogens presumably allows preferential deprotonation of the xanthene rings.

Ultrafast Optical Study Of Small Gold Monolayer Protected Clusters: A Closer Look At Emission, S. Hei Yau, O. Varnavski, John D. Gilbertson, Bert D. Chandler, G. Ramakrishna, T. Goodson

Chemistry Faculty Research

Monolayer-protected metal nanoclusters (MPCs) were investigated to probe their fundamental excitation and emission properties. In particular, gold MPCs were probed by steady-state and time-resolved spectroscopic measurements; the results were used to examine the mechanism of emission in relation to the excited states in these systems. In steady-state measurements, the photoluminescence of gold clusters in the range of 25 to 140 atoms was considerably stronger relative to larger particle analogues. The increase in emission efficiency (for Au₂₅, Au₅₅, and Au₁₄₀ on the order of 10^-5) over bulk gold may arise from a different mechanism …

Spontaneously Generated Atomic Entanglement In Free Space Reinforced By Incoherent Pumping, Ling Zhou, Gou Hui Yang, Anil K. Patnaik

Physics Faculty Publications

We study spontaneously generated entanglement (SGE) between two identical multilevel atoms in free space via vacuum-induced radiative coupling. We show that the SGE in two-atom systems may initially increase with time but eventually vanishes in the time scale determined by the excited-state lifetime and radiative coupling strength between the two atoms. We demonstrate that steady-state SGE can be established by incoherently pumping the atoms to their excited states. We have shown that an appropriate rate of incoherent pump can help in producing optimal steady-state SGE. The multilevel systems offer us more channels to establish entanglement. The system under consideration can …

Ionization And Ionization-Excitation Of Helium To The N=1-4 States Of He⁺ By Electron Impact, Susan M. Bellm, Julian C A Lower, Klaus Bartschat, Xiaoxu Guan, Daniel Weflen, Matthew S. Foster, Allison L. Harris, Don H. Madison

Physics Faculty Research & Creative Works

We present experimental and theoretical results for the electron-impact-induced ionization of ground-state helium atoms. Using a high-sensitivity toroidal electron spectrometer, we measured cross-section ratios for transitions leading to the first three excited states of the residual helium ion relative to the transition leaving the ion in the ground state. Measurements were performed for both symmetric- and asymmetric-energy-sharing kinematics. By presenting results as a ratio, a direct comparison can be made between theoretical and experimental predictions without recourse to normalization. The experimental data are compared to theoretical predictions employing various first-order models and a second-order hybrid distorted-wave + convergent R matrix …

Alignment Dynamics Of Slow Light Diffusion In Ultracold Atomic 85Rb, S. Balik, R. G. Olave, C. I. Sukenik, M. D. Havey, V. M. Datsyuk, I. M. Sokolov, D. V. Kupriyanov

Physics Faculty Publications

A combined experimental and theoretical investigation of time- and alignment-dependent propagation of light in an ultracold atomic gas of atomic ⁸⁵Rb is reported. Coherences among the scattering amplitudes for light scattering off excited hyperfine levels produce strong variations of the light polarization in the vicinity of atomic resonance. Measurements are in excellent agreement with Monte Carlo simulations of the multiple scattering process.

Double Excitations Within Time-Dependent Density Functional Theory Linear Response, Neepa T. Maitra, Fan Zhang, Robert J. Cave, Kieron Burke

All HMC Faculty Publications and Research

Within the adiabatic approximation, time-dependent density functional theory yields only single excitations. Near states of double excitation character, the exact exchange–correlation kernel has a strong dependence on frequency. We derive the exact frequency-dependent kernel when a double excitation mixes with a single excitation, well separated from the other excitations, in the limit that the electron–electron interaction is weak. Building on this, we construct a nonempirical approximation for the general case, and illustrate our results on a simple model.

Short-Pulse Laser-Induced Stabilization Of Autoionizing States, Heider N. Ereifej, J. Greg Story

Physics Faculty Research & Creative Works

Atoms in doubly excited states above the first ionization limit can decay via autoionization in which an electron is emitted leaving an ion, or by photoemission which leaves the atom in a singly excited state. In this paper, it is demonstrated that interaction between the atoms and a laser pulse that is short compared to the autoionization lifetime can lead to large enhancement of the photoemission process by stimulating the atoms to emit a photon. Since the resultant singly excited atoms do not autoionize, this process can be viewed as an enhancement of the stabilization of the doubly excited atoms …

Role Of Spontaneous Emission In Ultracold Two-Color Optical Collisions, C. I. Sukenik, T. Walker

Physics Faculty Publications

We have observed violet photon emission resulting from energy-pooling collisions between ultracold Rb atoms illuminated by two colors of near-resonant infrared laser light. We have used this emission as a probe of doubly excited state ultracold collision dynamics. By varying the detuning of the lasers, we have clearly identified the effect of spontaneous emission on the collision process.

Low Saturation Intensities In Two-Photon Ultracold Collisions, C. I. Sukenik, D. Hoffman, S. Bali, T. Walker

Physics Faculty Publications

We have observed violet photon emission resulting from energy-pooling collisions between ultracold Rb atoms illuminated by two colors of near-resonant infrared laser light. We have used this emission as a probe of doubly excited state ultracold collision dynamics. We have observed the lowest saturation intensity for light-induced ultracold collisions seen to date which we identify as due to depletion of incoming ground state flux. We have also varied the detuning of the lasers which allows us to clearly identify the effect of spontaneous emission and optical shielding.

Calculation Of Electronic Coupling Matrix Elements For Ground And Excited State Electron Transfer Reactions: Comparison Of The Generalized Mulliken–Hush And Block Diagonalization Methods, Robert J. Cave, Marshall D. Newton

All HMC Faculty Publications and Research

Two independent methods are presented for the nonperturbative calculation of the electronic coupling matrix element (Hab) for electron transfer reactions using ab initio electronic structure theory. The first is based on the generalized Mulliken–Hush (GMH) model, a multistate generalization of the Mulliken Hush formalism for the electronic coupling. The second is based on the block diagonalization (BD) approach of Cederbaum, Domcke, and co-workers. Detailed quantitative comparisons of the two methods are carried out based on results for (a) several states of the system Zn2OH2+ and (b) the low-lying states of the benzene–Cl atom complex and its contact ion pair. Generally …