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Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters

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A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (31 May 2023) | Viewed by 18463

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Special Issue Editors

Prof. Dr. Himadri S. Chakraborty

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Guest Editor

Department of Natural Sciences, Northwest Missouri State University, Maryville, MO 64468, USA
Interests: theoretical AMO physics; photoabsorption of atoms, fullerenes, endofullerenes; photoemission time delay; relaxation/thermalization of hot electrons in fullerene systems; positronium formation; ion-surface charge transfer collisions

Dr. Hari R. Varma

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Guest Editor

School of Physical Sciences, Indian Institute of Technology - Mandi, Kamand, Mandi 175075, Himachal Pradesh, India
Interests: structure and dynamics of atoms, clusters; photoionization studies of endohedral systems; Wigner time delay studies; electron impact studies on fullerenes

Special Issue Information

Dear Colleagues,

This Special Issue aims to publish new and impactful research on fundamental and advanced studies investigating the interactions of atomic, molecular or cluster systems with radiation or impacting charge particles.

Submissions should present novel effects, mechanisms and phenomena in the energy response (spectroscopy) and the time evolution (dynamics) of excited target systems, highlighting new experimental techniques and powerful theoretical/computational methods and instigating novel questions to motivate future research and collaboration.

There have been three recent developments in AMO and cluster science: a) new and progressively precise technologies to synthesize materials with good purity statistics in gas-phase, as thin films, or in liquid-phase; b) significant diversification of pump–probe laser and particle sources, and related experimental techniques for accessing both the energy response and temporal response in ultrafast time scales of the target materials; and c) increasing availability of high-performance computer software on ever faster computers, processed in series and in parallel modes. These developments have empowered the broader AMO community to address more detailed and critical aspects of response and relaxation processes. As a result, many groups have become involved in ever-more challenging and complex investigations pushing the frontier of knowledge. The planned Special Issue will provide a forum in which to broadcast emerging research results, creating a professional knowledge repository of novel research questions and outlooks, and stimulating brand-new collaborations.

The bulk of topics that this Issue will cover is also published in American Physical Society, American Institute of Physics, Institute of Physics UK and European Physics journals, besides in regular issues of Atoms, a journal published by MDPI. Potential authors will have past and future publications in these journals stemming from their broader programs and collaborations. We hope that the material published in this Special Issue will substantially complement research published elsewhere. In particular, given the open access nature of Atoms, this Issue aims to widen readership through engagement with scientific connections and cross-citations.

Prof. Dr. Himadri S. Chakraborty
Dr. Hari R. Varma
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atoms is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

ultrafast
attosecond
femtosecond
diffraction
relaxation
decay
excitation
ionization
fragmentation
high-harmonic
endohedral
plasmonics
electron collision
positron collision

Published Papers (14 papers)

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Editorial

Jump to: Research, Other

5 pages, 213 KiB

Open AccessEditorial

Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules and Clusters

by Himadri S. Chakraborty and Hari R. Varma

Atoms 2023, 11(12), 156; https://doi.org/10.3390/atoms11120156 - 12 Dec 2023

Viewed by 1196

Abstract

Atomic, molecular, and optical (AMO) physics is a vastly important sub-discipline [...] Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

Research

Jump to: Editorial, Other

13 pages, 3453 KiB

Open AccessArticle

Fragmentation of Multiply Charged C₁₀H₈ Isomers Produced in keV Range Proton Collision

by Meloottayil V. Vinitha, Pragya Bhatt, Cholakka P. Safvan, Sarita Vig and Umesh R. Kadhane

Atoms 2023, 11(11), 138; https://doi.org/10.3390/atoms11110138 - 25 Oct 2023

Viewed by 1072

Abstract

The dissociation of multiply charged C₁₀H₈ isomers produced in fast proton collisions (velocities between 1.41 and 2.4 a.u.) is discussed in terms of their fundamental molecular dynamics, in particular the processes that produce different carbon clusters in such a collision. [...] Read more.

^{+}

and CH_n⁺ (n = 0 to 3). The elimination of H

^{+}

^{+}

is found to be significantly different from CH₃⁺ loss. The loss of CH₃⁺ proceeds through a cascade of momentum-correlated dissociations with the formation of heavy ions such as C₉H₅⁺, C₉H₅²⁺ and C₇H₃⁺. The structure of such large fragment ions is predicted with the help of their calculated ground state electronic energies and the multi-hit time-of-flight (ToF) correlation between the second and third hit fragments if detected. Furthermore, we report experimentally the super-dehydrogenation of naphthalene and azulene targets, with evidence of complete dehydrogenation in a single collision. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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13 pages, 5848 KiB

Open AccessArticle

Quadrupole Effects in the Photoionisation of Sodium 3s in the Vicinity of the Dipole Cooper Minimum

by Nishita M. Hosea, Jobin Jose, Hari R. Varma, Pranawa C. Deshmukh and Steven T. Manson

Atoms 2023, 11(10), 125; https://doi.org/10.3390/atoms11100125 - 28 Sep 2023

Viewed by 1105

Abstract

A procedure to obtain relativistic expressions for photoionisation angular distribution parameters using the helicity formulation is discussed for open-shell atoms. Electric dipole and quadrupole transition matrix elements were considered in the present work, to study the photoionisation dynamics of the 3s electron of the sodium atom in the vicinity of the dipole Cooper minimum. We studied dipole–quadrupole interference effects on the photoelectron angular distribution in the region of the dipole Cooper minimum. Interference with quadrupole transitions was found to alter the photoelectron angular distribution, even at rather low photon energies. The initial ground and final ionised state discrete wavefunctions of the atom were obtained in the present work using GRASP, and we employed RATIP with discrete wavefunctions, to construct continuum wavefunctions and to calculate transition amplitudes, total cross-sections and angular distribution asymmetry parameters. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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13 pages, 10937 KiB

Open AccessArticle

Density Functional Treatment of Photoionization of Sodium Clusters: Effects of Cluster Size and Exchange–Correlation Framework

by Rasheed Shaik, Hari R. Varma and Himadri S. Chakraborty

Atoms 2023, 11(8), 114; https://doi.org/10.3390/atoms11080114 - 18 Aug 2023

Viewed by 850

Abstract

The ground state and photoionization properties of Na

_{x}

The ground state and photoionization properties of Na

_{x}

(x = 20, 40, and 92) clusters are investigated using a method based on density functional theory (DFT) in a spherical jellium frame. Two different exchange–correlation treatments with the Gunnarsson–Lundqvist parametrization are used: (i) the electron self-interaction correction (SIC) scheme and (ii) the van Leeuwen–Baerends (LB94) scheme based on the gradient of the electron density. The shapes of the mean-field potentials and bound state properties, obtained in the two schemes, qualitatively agree, but differ in the details. The effect of the schemes on the photoionization dynamics, calculated in linear response time-dependent DFT is compared, in which the broader features are found to be universal. The general similarity of the results in SIC and LB94 demonstrates the reliability of DFT treatments. The study further elucidates the evolution of the ground state and ionization description as a function of the cluster size. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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22 pages, 433 KiB

Open AccessArticle

Transitional Strength under Plasma: Precise Estimations of Astrophysically Relevant Electromagnetic Transitions of Ar⁷⁺, Kr⁷⁺, Xe⁷⁺, and Rn⁷⁺ under Plasma Atmosphere

by Swapan Biswas, Anal Bhowmik, Arghya Das, Radha Raman Pal and Sonjoy Majumder

Atoms 2023, 11(6), 87; https://doi.org/10.3390/atoms11060087 - 25 May 2023

Viewed by 989

Abstract

The growing interest in atomic structures of moderately stripped alkali-like ions in the diagnostic study and modeling of astrophysical and laboratory plasma makes an accurate many-body study of atomic properties inevitable. This work presents transition line parameters in the absence or presence of plasma atmosphere for astrophysically important candidates Ar⁷⁺, Kr⁷⁺, Xe⁷⁺, and Rn⁷⁺. We employ relativistic coupled-cluster (RCC) theory, a well-known correlation exhaustive method. In the case of a plasma environment, we use the Debye Model. Our calculations agree with experiments available in the literature for ionization potentials, transition strengths of allowed and forbidden selections, and lifetimes of several low-lying states. The unit ratios of length and velocity forms of transition matrix elements are the critical estimation of the accuracy of the transition data presented here, especially for a few presented for the first time in the literature. We do compare our findings with the available recent theoretical results. Our reported data can be helpful to the astronomer in estimating the density of the plasma environment around the astronomical objects or in the discovery of observational spectra corrected by that environment. The present results should be advantageous in the modeling and diagnostics laboratory plasma, whereas the calculated ionization potential depression parameters reveal important characteristics of atomic structure. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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14 pages, 1562 KiB

Open AccessArticle

Attosecond Time Delay Trends across the Isoelectronic Noble Gas Sequence

by Brock Grafstrom and Alexandra S. Landsman

Atoms 2023, 11(5), 84; https://doi.org/10.3390/atoms11050084 - 15 May 2023

Cited by 1 | Viewed by 1166

Abstract

The analysis and measurement of Wigner time delays can provide detailed information about the electronic environment within and around atomic and molecular systems, with one the key differences being the lack of a long-range potential after a halogen ion undergoes photoionization. In this work, we use relativistic random-phase approximation to calculate the average Wigner delay from the highest occupied subshells of the atomic pairings (2p, 2s in Fluorine, Neon), (3p, 3s in Chlorine, Argon), (4p, 4s, 3d, in Bromine, Krypton), and (5p, 5s, 4d in Iodine, Xenon). The qualitative behaviors of the Wigner delays between the isoelectronic pairings were found to be similar in nature, with the only large differences occurring at photoelectron energies less than

20 e V

and around Cooper minima. Interestingly, the relative shift in Wigner time delays between negatively charged halogens and noble gases decreases as atomic mass increases. All atomic pairings show large differences at low energies, with noble gas atoms showing large positive Wigner delays, while negatively charged halogen ions show negative delays. The implications for photoionization studies in halide-containing molecules is also discussed. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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18 pages, 2330 KiB

Open AccessArticle

Projectile Coherence Effects in Twisted Electron Ionization of Helium

by A. L. Harris

Atoms 2023, 11(5), 79; https://doi.org/10.3390/atoms11050079 - 03 May 2023

Cited by 1 | Viewed by 1562

Abstract

Over the last decade, it has become clear that for heavy ion projectiles, the projectile’s transverse coherence length must be considered in theoretical models. While traditional scattering theory often assumes that the projectile has an infinite coherence length, many studies have demonstrated that the effect of projectile coherence cannot be ignored, even when the projectile-target interaction is within the perturbative regime. This has led to a surge in studies that examine the effects of the projectile’s coherence length. Heavy-ion collisions are particularly well-suited to this because the projectile’s momentum can be large, leading to a small deBroglie wavelength. In contrast, electron projectiles that have larger deBroglie wavelengths and coherence effects can usually be safely ignored. However, the recent demonstration of sculpted electron wave packets opens the door to studying projectile coherence effects in electron-impact collisions. We report here theoretical triple differential cross-sections (TDCSs) for the electron-impact ionization of helium using Bessel and Laguerre-Gauss projectiles. We show that the projectile’s transverse coherence length affects the shape and magnitude of the TDCSs and that the atomic target’s position within the projectile beam plays a significant role in the probability of ionization. We also demonstrate that projectiles with large coherence lengths result in cross-sections that more closely resemble their fully coherent counterparts. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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16 pages, 2603 KiB

Open AccessArticle

Fragmentation Dynamics of

{CO}_{2}^{q +}

(q = 2, 3) in Collisions with 1 MeV Proton

by Avijit Duley and Aditya. H. Kelkar

Atoms 2023, 11(5), 75; https://doi.org/10.3390/atoms11050075 - 23 Apr 2023

Viewed by 1329

Abstract

The fragmentation dynamics of the CO

_{2}^{q +}

(q = 2, 3) molecular ions formed under the impact of 1 MeV protons is studied using a recoil ion momentum spectrometer equipped with a multi-hit time- and position-sensitive detector. Both two-body and three-body [...] Read more.

The fragmentation dynamics of the CO

_{2}^{q +}

_{2}

are identified and analyzed. Kinetic energy release (KER) distributions have been obtained for various channels. With the help of Dalitz plots and Newton diagrams concerted and sequential processes have been assigned to observed fragmentation channels. In addition, angular correlations are used to determine the molecular geometry of the precursor molecular ion. It is found that the symmetric breakup into C

^{+}

+ O

^{+}

+ O

^{+}

involves asymmetric stretching of the molecular bonds in CO

_{2}^{3 +}

prior to dissociation via concerted decay implying the fact that collisions with 1 MeV proton induces an asynchronous decay in CO

_{2}

. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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19 pages, 6377 KiB

Open AccessArticle

Temporal Response of Atoms Trapped in an Optical Dipole Trap: A Primer on Quantum Computing Speed

by S. Baral, Raghavan K. Easwaran, J. Jose, Aarthi Ganesan and P. C. Deshmukh

Atoms 2023, 11(4), 72; https://doi.org/10.3390/atoms11040072 - 10 Apr 2023

Viewed by 1706

Abstract

An atom confined in an optical dipole trap is a promising candidate for a qubit. Analyzing the temporal response of such trapped atoms enables us to estimate the speed at which quantum computers operate. The present work models an atom in an optical dipole trap formed using crossed laser beams and further examines the photoionization time delay from such confined atoms. We study noble gas atoms, such as Ne (Z = 10), Ar (Z = 18), Kr (Z = 36), and Xe (Z = 54). The atoms are considered to be confined in an optical dipole trap using X-ray Free Electron Lasers (XFEL). The present work shows that the photoionization time delay of the trapped atoms is different compared with that of the free atoms. This analysis alerts us that while talking about the speed of quantum computing, the temporal response of the atoms in the trapped environment must also be accounted for. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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8 pages, 904 KiB

Open AccessCommunication

Does Carrier Envelope Phase Affect the Ionization Site in a Neutral Diatomic Molecule?

by Alex Schimmoller, Harrison Pasquinilli and Alexandra S. Landsman

Atoms 2023, 11(4), 67; https://doi.org/10.3390/atoms11040067 - 04 Apr 2023

Cited by 1 | Viewed by 1217

Abstract

A recent work shows how to extract the ionization site of a neutral diatomic molecule by comparing Quantum Trajectory Monte Carlo (QTMC) simulations with experimental measurements of the final electron momenta distribution. This method was applied to an experiment using a 40-femtosecond infrared pulse, finding that a downfield atom is roughly twice as likely to be ionized as an upfield atom in a neutral nitrogen molecule. However, an open question remains as to whether an assumption of the zero carrier envelope phase (CEP) used in the above work is still valid for short, few-cycle pulses where the CEP can play a large role. Given experimentalists’ limited control over the CEP and its dramatic effect on electron momenta after ionization, it is desirable to see what influence the CEP may have in determining the ionization site. In this paper, we employ QTMC techniques to simulate strong-field ionization and electron propagation from neutral

N_{2}

using an intense 6-cycle laser pulse with various CEP values. Comparing simulated electron momenta to experimental data indicates that the ratio of down-to-upfield ions remains roughly 2:1 regardless of the CEP. This confirms that the ionization site of a neutral molecule is determined predominantly by the laser frequency and intensity, as well as the ground-state molecular wavefunction, and is largely independent of the CEP. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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13 pages, 1703 KiB

Open AccessArticle

Rigorous Negative Ion Binding Energies in Low-Energy Electron Elastic Collisions with Heavy Multi-Electron Atoms and Fullerene Molecules: Validation of Electron Affinities

by Alfred Z. Msezane and Zineb Felfli

Atoms 2023, 11(3), 47; https://doi.org/10.3390/atoms11030047 - 03 Mar 2023

Cited by 1 | Viewed by 1039

Abstract

Dramatically sharp resonances manifesting stable negative ion formation characterize Regge pole-calculated low-energy electron elastic total cross sections (TCSs) of heavy multi-electron systems. The novelty of the Regge pole analysis is in the extraction of rigorous and unambiguous negative ion binding energies (BEs), corresponding to the measured electron affinities (EAs) of the investigated multi-electron systems. The measured EAs have engendered the crucial question: is the EA of multi-electron atoms and fullerene molecules identified with the BE of the attached electron in the ground, metastable or excited state of the formed negative ion during a collision? Inconsistencies in the meaning of the measured EAs are elucidated and new EA values for Bk, Cf, Fm, and Lr are presented. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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11 pages, 1157 KiB

Open AccessArticle

Manifestations of Rabi Dynamics in the Photoelectron Energy Spectra at Resonant Two-Photon Ionization of Atom by Intense Short Laser Pulses

by Nenad S. Simonović, Duška B. Popović and Andrej Bunjac

Atoms 2023, 11(2), 20; https://doi.org/10.3390/atoms11020020 - 23 Jan 2023

Cited by 4 | Viewed by 1205

Abstract

We study the Rabi flopping of the population between the ground and excited 2p states of the hydrogen atom, induced by intense short laser pulses of different shapes and of carrier frequency

ω = 0.375

a.u. which resonantly couples the two states, and [...] Read more.

We study the Rabi flopping of the population between the ground and excited 2p states of the hydrogen atom, induced by intense short laser pulses of different shapes and of carrier frequency

ω = 0.375

a.u. which resonantly couples the two states, and manifestations of this dynamics in the energy spectra of photoelectrons produced in the subsequent ionization of the atom from the excited state. It is found that, for Gaussian, half-Gaussian and rectangular pulses, characterized by the same pulse area, the final populations take the same values and the spectra consist of similar patterns having the same number of peaks and approximately the same separation between the prominent edge (Autler–Townes) peaks. The additional analysis in terms of dressed states showed that the mechanism of formation of multiple-peak structures during the photoionization process is the same regardless of the pulse shape. These facts disprove the hypothesis proposed in earlier studies with Gaussian pulse, that the multiple-peak pattern appears due to dynamic interference of the photoelectrons emitted with a time delay at the rising and falling sides of the pulse, since the hypothesis is not applicable to either a half-Gaussian pulse that has no rising part or a rectangular pulse whose intensity is constant. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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6 pages, 1490 KiB

Open AccessOpinion

The Spin-Orbit Interaction: A Small Force with Large Implications

by Steven T. Manson

Atoms 2023, 11(6), 90; https://doi.org/10.3390/atoms11060090 - 02 Jun 2023

Viewed by 1013

Abstract

The spin-orbit interaction is quite small compared to electrostatic forces in atoms. Nevertheless, this small interaction can have large consequences. Several examples of the importance of the spin-orbit force in atomic photoionization are presented and explained. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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9 pages, 243 KiB

Open AccessOpinion

The Atom at the Heart of Physics

by Jean-Patrick Connerade

Atoms 2023, 11(2), 32; https://doi.org/10.3390/atoms11020032 - 06 Feb 2023

Viewed by 1412

Abstract

A number of reasons are advanced for which atoms stand at the heart of research in the physical sciences. There are issues in physics which are both fundamental and only partly resolved or, at least, imperfectly understood. Rather than chase them towards higher and higher energies, which mainly results in greater complexity, it makes sense to restrict oneself to the simplest systems known, held together by the best understood force in nature, viz. those governed by the inverse square law. Our line of argument complements the adage of Richard Feynman, who asked: should Armageddon occur, is there a simple, most important idea to preserve as a testament to human knowledge? The answer he suggested is: the atomic hypothesis. Full article

(This article belongs to the Special Issue Photon and Particle Impact Spectroscopy and Dynamics of Atoms, Molecules, and Clusters)

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