Narrow Results

In this work, the effects of an ultrashort laser pulse on the excitation and ionization dynamics of a hydrogen guested endofullerene system embedded in a quantum plasma environment under spherical encompassment are investigated. The interaction of the plasma environment is considered within the more general exponential cosine screened Coulomb (MGECSC) potential model, and the excitation and ionization dynamics are analyzed through plasma screening parameters. For endohedral confinement, the relevant model that aligns with experimental data and is most suitable for static endohedral encapsulation is the Woods–Saxon potential model. By considering different numerical ranges of the parameters in this model, the effects of various forms of fullerenes are thoroughly explained through the analysis of confinement depth, spherical shell thickness, inner radius and the smoothing parameters. The effects of the characteristic properties of the laser pulse, such as its intensity and frequency, on the probability dynamics are also discussed. All parameters and their respective ranges are important for optimizing system performance. Additionally, the alternatives of all parameters related to the plasma-embedded endofullerene system for probability dynamics are considered. In this context, the findings cause new ideas in the controlled excitation and ionization processes of endofullerene systems embedded in a quantum plasma environment and provide a significant foundation for future experimental studies.

We study the evolution of a one-dimensional model atom with δ-function binding potential, subjected to a dipole radiation field E(t)x with E(t) a 2π/ω-periodic real-valued function. We prove that when E(t) is a trigonometric polynomial, complete ionization occurs, i.e. the probability of finding the electron in any fixed region goes to zero as t → ∞.

For ψ(x, t = 0) compactly supported and general periodic fields, we decompose ψ(x, t) into uniquely defined resonance terms and a remainder. Each resonance is 2π/ω periodic in time and behaves like the exponentially growing Green's function near x = ±∞. The remainder is given by an asymptotic power series in t^-1/2 with coefficients varying with x.

Fully differential studies of single ionization of neutral atoms by charged particle impact have proven to be extremely powerful to advance our understanding of the few-body dynamics in atomic processes. Until a few years ago, such data were only available for electron impact and were mostly limited to electrons ejected into the scattering plane. When fully differential data were finally obtained for ion impact covering the entire three-dimensional space, very surprising features were observed. It then became clear that our understanding of ionization processes in atomic collisions is not nearly as complete as previously assumed. Here, we review the development of experimental and theoretical studies of three-dimensional fully differential single ionization cross-sections since then.

A multifaceted experimental study of collisions of Na${}^{+}$ and K${}^{+}$ ions in the energy range of 0.5–10 keV with He and Ar atoms is presented. Absolute cross-sections for charge-exchange, ionization, stripping and excitation processes were measured using a refined version of the transfer electric field method, angle- and energy-dependent collection of product ions, energy loss and optical spectroscopy methods. The experimental data and the schematic correlation diagrams are employed to analyze and determine the mechanisms for these processes.

We study the static properties of water tetramer in ground state, the optical absorption spectra and ultrafast nonadiabatic dynamical response of water tetramer to short and intense laser pulses with different intensities by a real-space, real-time implementation of time-dependent density functional theory coupled to molecular dynamics (TDDFT–MD) nonadiabatically. The calculated results are in good agreement with available values in literature. Four typical irradiated scenarios of water tetramer in laser field, which are “normal vibration,” “break and reorganization,” “fragmentation and new formation” and “pure fragmentation”, are explored by discussing the ionization, the bond lengths of OH bonds and hydrogen bonds and the kinetic energy of ions. The dynamic simulation shows that the reaction channel of water tetramer can really be controlled by choosing appropriate laser parameters referring to the optical absorption spectra and hydrogen ions play an important role in the reaction channel. Furthermore, it is found that the laser intensity affects the kinetic energy of ejected protons more than that of the remaining fragments and all dynamic processes are somehow directly related to the velocity of departing protons.

The electron-ion dynamics of hydroperoxyl radical in intense femtosecond laser pulses is studied by using time-dependent density functional theory combined with molecular dynamics approach. We calculate the optimized structure, the ionization energy, and the optical absorption strength. The results are in good agreement with experiments. The irradiation dynamics of HO₂ including the ionization, the dipole moment, the bond lengths, the kinetic energies, and the level depletion is explored by varying the laser frequency. Computational results indicate that the excitation behaviors are distinct due to different frequencies. Furthermore, the angular dependence of the total ionization and the orbital ionization yields of HO₂ are explored. The calculated result predicts a maximum around $40^{\circ }$ and $220^{\circ }$ for the total ionization and the angular dependence of the total ionization reflects the symmetry of the HOMO.

We study the electron-impact induced ionization of O₂ from threshold to 120 eV using the electron spectroscopy method. Our approach is simple in concept and embodies the ion source with a collision chamber and a mass spectrometer with a quadruple filter as a selector for the product ions. The combination of these two devices makes it possible to unequivocally collect all energetic fragment ions formed in ionization and dissociative processes and to detect them with known efficiency. The ion source allows varying and tuning the electron-impact ionization energy and the target-gas pressure. We demonstrate that for obtaining reliable results of cross-sections for inelastic processes and determining mechanisms for the formation of O${}^{+}{(}^{4}S,{}^{2}D,{}^{2}P)$ ions, it is crucial to control the electron-impact energy for production of ion and the pressure in the ion source. A comparison of our results with other experimental and theoretical data shows good agreement and proves the validity of our approach.

In this paper, we study the electronic and ionic dynamics of the water dimer subject to short and intense laser pulses. The dynamics is described by means of the time-dependent local-density approximation coupled to ionic molecular dynamics (TDLDA-MD) non-adiabatically. The impact of laser frequency on the response of water dimer is discussed by exploring the ionization, the dipole signal and bond lengths of water dimer. Furthermore, it is found that the water donor is more sensitive to the laser field than the water acceptor and the probabilities for the ionic states show the general pattern of the typical sequence of the interlaced production maxima.

The structural and elastic properties of neutral and ionized dichlorocarbene (CCl₂) functionalized single-walled carbon nanotubes (SWCNTs) were studied using density functional theory (DFT). The Young’s modulus of ionized pristine SWCNTs is found to decrease in comparison to that of neutral models. The interesting effect of increase in Young’s modulus values of ionized functionalized SWCNTs is observed. We ascribe this feature to the concurrent processes of the bond elongation on ionization and the local deformation on cycloaddition. The strong dependence of the elasticity modulus on the number of addends is also observed. However, the CCl₂-attached SWCNTs in their neutral and ionized forms remain strong enough to be suitable for the reinforcement of composites. In contrast to the elastic properties, the binding energies do not change significantly, irrespective of CCl₂ coverage.

With the help of the time-dependent local-density approximation (TDLDA) coupled non-adiabatically to molecular dynamics (MD), we studied both the static properties and irradiation dynamics of water trimer subject to the short and intense femtosecond laser field. It is shown that the optimized geometry and the optical absorption strength of the water trimer accord well with results in literature. Three typical possible irradiated scenarios of water trimer which are “normal oscillation”, “dissociation and formation” and “pure OH dissociation” are exhibited by investigating the ionization and the level depletion related to electrons as well as the OH bonds, proton-transfer, the intermolecular distance and the kinetic energy connected with ions. In three scenarios, the behaviors of water trimer can be attributed to the sequential combination of responses of the electrons emission, the proton-transfer, OH vibration and rotation, OH dissociation and hydroxyl formation, respectively. The relevant time scales of the first proton-transfer and OH dissociation are identified as 13 fs and 10–20 fs, respectively. The study of kinetic energies of ions show that the kinetic energies of the remaining ions are all below 4.5 eV and outgoing hydrogen ions carry a kinetic energy about 5–12 eV. Furthermore, it is found that in the tunneling ionization situations the depletion is fairly shared between the various levels except the most deep occupied electronic level while in the multiphotonic ionization case the electron loss comes from all single-electron levels and the HOMO level contributes the most.

The performance of magnetohydrodynamic (MHD) power generator is affected by many issues, among which the load coefficient k is of great importance. This paper reveals the relationship between the k and the performance of MHD generator by numerical simulation on Faraday-type MHD power generator using He/Xe as working plasma. The results demonstrate that the power generation efficiency increases with an increment of the load factor. However, the enthalpy extraction firstly increases then decreases with the load factor increasing. The enthalpy extraction rate reaches the maximum when the load coefficient k equals to 0.625, which infers the best performance of the power generator channel with the maximum electricity production.

So far, one of the most promising applications of nanoscale science and technology has been in the area of field emission. The electric field amplification effects associated with sharp nanostructure tips can be used to significantly reduce the emission voltages. Another equally promising area that also takes advantage of the field amplification effects is the area of field ionization. The extremely high electrical fields generated near the vicinity of sharp nanostructure tips can be used to ionize chemical or biological species at a fraction of the voltage of a traditional ionizer. In this article we review two of the very first reported papers related to nanoscale field ionization published by our group at the Rensselaer Polytechnic Institute. The first paper describes a carbon nanotube gas ionizer, which shows potential for gas sensing applications. The second paper describes an ultra low-power gas ionizer featuring β-phase Tungsten nanorod electrodes. We end with a review of the major challenges that must be overcome to develop nanoscale ionization sensors.