Atomic And Molecular Clusters

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Efimov universality with Coulomb interaction (1901.03643v3)

C. H. Schmickler, H. -W. Hammer, E. Hiyama

2019-01-11

The universal properties of charged particles are modified by the presence of a long-range Coulomb interaction. We investigate the modification of Efimov universality as a function of the Coulomb strength using the Gaussian expansion method. The resonant short-range interaction is described by Gaussian potentials to which a Coulomb potential is added. We calculate binding energies and root mean square radii for the three- and four-body systems of charged particles and present our results in a generalised Efimov plot. We find that universal features can still be discerned for weak Coulomb interaction, but break down for strong Coulomb interaction. The root-mean-square radius plateaus at increasingly smaller values for strong Coulomb interaction and the probablity distributions of the states become more concentrated inside the Coulomb barrier. As an example, we apply our universal model to nuclei with an alpha-cluster substructure. Our results point to strong non-universal contributions in that sector.

Crystalline droplets with emergent topological color-charge in many-body systems with sign-changing interactions (1905.13217v1)

P. Karpov, F. Piazza

2019-05-30

We introduce a novel type of self-bound droplet which carries an emergent color-charge. We consider a system of particles hopping on a lattice and interacting via a commensurately sign-changing potential which is attractive at short range. The droplet formation is heralded by spontaneous crystallization into topologically distinct domains. This endows each droplet with an emergent color-charge governing their mutual interactions: attractive for equal colors and repulsive otherwise. The number of allowed colors is fixed only by the discrete spatial symmetries of the interaction potential. With increasing interaction range, the droplets become progressively more mobile, with their color-charge still being energetically protected, allowing for non-trivial viscous dynamics of the interacting droplet plasmas formed during cooling. Sign-changing potentials with short-range attraction appear quite naturally for light-mediated interactions and we concretely propose a realization in state-of-the-art experiments with cold atoms in a multimode optical cavity.

Dissociation dynamics in the dissociative electron attachment to ammonia molecule (1905.10993v1)

Dipayan Chakraborty, Aranya Giri, Dhananjay Nandi

2019-05-27

Complete dissociation dynamics of low energy electron attachment to ammonia molecule has been studied using velocity slice imaging (VSI) spectrometer. One low energy resonant peak around 5.5 eV and a broad resonance around 10.5 eV incident electron energy has been observed. The resonant states mainly dissociate via H and NH fragments, though for the upper resonant state, signature of NH fragments are also predicted due to three body dissociation process. Kinetic energy and angular distributions of the NH fragment anions are measured simultaneously using VSI technique. Based on our experimental observations, we find the signature of A symmetry in the 10.5 eV resonance energy whereas, the 5.5 eV resonance is associated with the well known A symmetry.

The water-carbon monoxide dimer: new infrared spectra, ab initio rovibrational energy level calculations, and an interesting intermolecular mode (1905.10903v1)

A. Barclay, A. van der Avoird, A. R. W. McKellar, N. Moazzen-Ahmadi

2019-05-26

Rovibrational energy level calculations using a high-level intermolecular potential surface are reported for H2O-CO and D2O-CO. They predict the ground K = 1 levels to lie about 20 (12) cm-1 above K = 0 for H2O-CO (D2O-CO) in good agreement with past experiment. But the first excited K = 1 levels are predicted to lie about 3 cm-1 below their K = 0 counterparts in both cases. Intensity calculations also indicate that mid-infrared transitions from the K = 0 ground state to this seemingly anomalous excited K = 1 state should be observable. These predictions are strikingly verified by new spectroscopic measurements covering the C-O stretch region around 2200 cm-1 for H2O-CO, D2O-CO, and HOD-CO, and the O-D stretch region around 2700 cm-1 for D2O-CO, HOD-CO, and DOH-CO. The experiments probe a pulsed supersonic slit jet expansion using tunable infrared quantum cascade laser or optical parametric oscillator sources. Discrete perturbations in the O-D stretch region give an experimental lower limit of about 340 cm-1 for D2O-CO, as compared to our calculated binding energy of 368 cm-1. Wavefunction plots are presented to help understand the intermolecular dynamics of H2O-CO. Coriolis interactions are invoked to explain the seemingly anomalous energies of the first excited K = 1 levels.

Photoionization of Molecular Endohedrals (1905.09739v1)

M. Ya. Amusia, L. V. Chernysheva, S. K. Semenov

2019-05-23

We calculate the photoionization cross-section of a molecular endohedral. We limit ourselves to two-atomic molecules. The consideration is much more complex than for atomic endohedrals because the system even for almost spherical fullerenes has only cylindrical instead of spherical symmetry. On the other hand, molecular endohedral is more interesting since the interelectron interaction in molecules is relatively stronger than in similar atoms. We present here results of calculations of molecular hydrogen stuffed inside almost spherical fullerene. For comparison, we perform calculations also for atomic endohedral with Helium inside fullerene. The results are obtained both in the single-electron Hartree-Fock approximation and with account of multi-electron correlations in the frame of so-called random phase approximation with exchange. The presence of the fullerenes shell results in prominent oscillations in the endohedrals photoionization cross section. The role of interelectron correlations becomes clear by comparing HF and RPAE results for molecular and atomic endohedral on the one side with that for corresponding isolated molecule and atom on the other.

Metrology of time-domain soft X-ray attosecond pulses and re-evaluation of pulse durations of three recent experiments (1905.09526v1)

Zhao Xi, Wang Su-Ju, Yu Wei-Wei, Wei Hui, Lin C. D

2019-05-23

Attosecond pulses in the soft-X-ray (SXR) to water-window energy region offer the tools for creating and studying target specific localized inner-shell electrons or holes in materials, enable monitoring or controlling charge and energy flows in a dynamic system on attosecond timescales. Recently, a number of laboratories have reported generation of continuum harmonics in the hundred-electron-volt to kilovolt region with few-cycle long-wavelength mid-infrared lasers. These harmonics have the bandwidth to support pulses with duration of few- to few-ten attoseconds. But harmonics generated in a gas medium have attochirps that cannot be fully compensated by materials over a broad spectral range; thus, realistically what are the typical shortest attosecond pulses that one can generate? To answer this question, it is essential that the temporal attosecond pulses be accurately characterized. By re-analyzing the soft X-ray harmonics reported in three recent experiments \cite{chang_natcom2017,Thomas_OE2017,Bieger_2017PRX} using a newly developed broadband phase retrieval algorithm, we show that their generated attosecond pulses are all longer than about 60 as. Since broadband pulses tend to have high-order chirps away from the spectral center of the pulse, the algorithm has to be able to retrieve accurately the phase over the whole bandwidth. Our re-evaluated pulse durations are found to be longer than those previously reported. We also introduce the autocorrelation (AC) of the streaking spectrogram. By comparing the ACs from the experiments and from the retrieved SXR pulses, the accuracy of the retrieved results can be directly visualized to ensure that correct phases have been obtained. Our retrieval method is fast and accurate, and it shall provide a powerful tool for the metrology of few-ten-attosecond pulses in the future.

First Principles Study of Structural and Optical Properties of B Isomers (1802.01072v2)

Pritam Bhattacharyya, Ihsan Boustani, Alok Shukla

2018-02-04

In this work we undertake a comprehensive numerical study of the ground state structures and optical absorption spectra of isomers of B cluster. Geometry optimization was performed at the coupled-cluster-singles-doubles (CCSD) level of theory, employing cc-pVDZ extended basis sets. Once the geometry of a given isomer was optimized, its ground state energy was calculated more accurately at the coupled-cluster-singles-doubles along with perturbative treatment of triples (CCSD(T)) level of theory, employing larger cc-pVTZ basis sets. Thus, our computed values of binding energies of various isomers are expected to be quite accurate. Our geometry optimization reveals eleven distinct isomers, along with their point group, and electronic ground state symmetries. We also performed vibrational frequency analysis on the three lowest energy isomers, and found them to be stable. Therefore, we computed the linear optical absorption spectra of these isomers of B, employing large-scale multi-reference singles-doubles configuration-interaction (MRSDCI) approach, and found a strong structure-property relationship. This implies that the spectral fingerprints of the geometries can be utilized for optical detection, and characterization, of various isomers of B. We also explored the stability of the isomer with with the structure of a perfect icosahedron, with symmetry. In bulk boron icosahedron is the basic structural unit, but, our vibrational frequency analysis reveals that it is unstable in the isolated form. We speculate that this instability could be due to Jahn-Teller distortion because five-fold degenerate HOMO orbitals in structure are unfilled.

van der Waals density functional with corrected coefficients (1905.07757v1)

K. Berland, D. Chakraborty, T. Thonhauser

2019-05-19

The non-local van der Waals density functional (vdW-DF) has had tremendous success since its inception in 2004 due to its constraint-based formalism that is rigorously derived from a many-body starting point. However, while vdW-DF can describe binding energies and structures for van der Waals complexes and mixed systems with good accuracy, one long-standing criticism---also since its inception---has been that the coefficients that derive from the vdW-DF framework are largely inaccurate and can be wrong by more than a factor of two. It has long been thought that this failure to describe the coefficients is a conceptual flaw of the underlying plasmon framework used to derive vdW-DF. We prove here that this is not the case and that accurate coefficient can be obtained without sacrificing the accuracy at binding separations from a modified framework that is fully consistent with the constraints and design philosophy of the original vdW-DF formulation. Our design exploits a degree of freedom in the plasmon-dispersion model , modifying the strength of the long-range van der Waals interaction and the cross-over from long to short separations, with additional parameters tuned_ to reference systems. Testing the new formulation for a range of different systems, we not only confirm the greatly improved description of coefficients, but we also find excellent performance for molecular dimers and other systems. The importance of this development is not necessarily that particular aspects such as coefficients or binding energies are improved, but rather that our finding opens the door for further conceptual developments of an entirely unexplored direction within the exact same constrained-based non-local framework that made vdW-DF so successful in the first place.

Coherent multidimensional spectroscopy in the gas phase (1905.06129v1)

Lukas Bruder, Ulrich Bangert, Marcel Binz, Daniel Uhl, Frank Stienkemeier

2019-05-15

Recent work applying multidimentional coherent electronic spectroscopy at dilute samples in the gas phase is reviewed. The development of refined phase-cycling approaches with improved sensitivity has opened-up new opportunities to probe even dilute gas-phase samples. In this context, first results of 2-dimensional spectroscopy performed at doped helium droplets reveal the femtosecond dynamics upon electronic excitation of cold, weakly-bound molecules, and even the induced dynamics from the interaction with the helium environment. Such experiments, offering well-defined conditions at low temperatures, are potentially enabling the isolation of fundamental processes in the excitation and charge transfer dynamics of molecular structures which so far have been masked in complex bulk environments.

Reactive molecular dynamics simulations of organometallic compound W(CO)6 fragmentation (1905.05507v1)

Pablo de Vera, Alexey Verkhovtsev, Gennady Sushko, Andrey V. Solov'yov

2019-05-14

Irradiation- and collision-induced fragmentation studies provide information about geometry, electronic properties and interactions between structural units of various molecular systems. Such knowledge brings insights into irradiation-driven chemistry of molecular systems which is exploited in different technological applications. An accurate atomistic-level simulation of irradiation-driven chemistry requires reliable models of molecular fragmentation which can be verified against mass spectrometry experiments. In this work fragmentation of a tungsten hexacarbonyl, W(CO), molecule is studied by means of reactive molecular dynamics simulations. The quantitatively correct fragmentation picture including different fragmentation channels is reproduced. We show that distribution of the deposited energy over all degrees of freedom of the parent molecule leads to thermal evaporation of CO groups and the formation of W(CO) () fragments. Another type of fragments, WC(CO) (), is produced due to cleavage of a C--O bond as a result of the localized energy deposition. Calculated fragment appearance energies are in good agreement with experimental data. These fragmentation mechanisms have a general physical nature and should take place in radiation-induced fragmentation of different molecular and biomolecular systems.

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