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We present the results of theoretical–computational studies of inter-particle energy transfer caused by elastic electron–ion collisions in expanding $$(\hbox {H}^{+})_{\mathrm {N}} +$$ electrons and $$\left( \mathrm {N}\mathrm {e}^{{8+}} \right) _{\mathrm {N}} +$$ electrons nanoplasmas, which are produced from clusters driven by near-infrared femtosecond, intense laser pulses. In these nanoplasmas, the short-range part of the electron–ion interactions is attractive for the $$\hbox {H}^{+}$$ ions and repulsive for the $$\mathrm {N}\mathrm {e}^{{8+}}$$ ions. The electron–ion collision times are ultrashort with $$\uptau = 10-20$$ as (attoseconds) for $$\left( \mathrm {N}\mathrm {e}^{\mathrm {8+}} \right) _{\mathrm {N}} +$$ electrons nanoplasmas and $$\uptau = 10$$ –50 as for ( $$\hbox {H}^{+})_{\mathrm {N}} +$$ electrons nanoplasmas. The collisional inter-particle energy transfers (CIET) are two-directional, occurring either from an electron to an ion or vice versa. The magnitude of the separate energy transfer processes depends on the kinetic energies of both colliding particles as well as on the collision geometry. While our previous studies dealt with periphery ions, the present work considers the collisional energy transfer within the entire clusters, where the relation between electron to ion and ion to electron energy transfers was found to be close to balance, providing on average a low net collisional energy transfer to ions. In the clusters’ inner cores this energy transfer presents 2–4% of the final ion energies in the $$\left( \mathrm {N}\mathrm {e}^{\mathrm {8+}} \right) _{\mathrm {N}}$$ clusters and less than 1% in the $$\left( \mathrm {H}^{+} \right) _{\mathrm {N}}$$ clusters, being lower in the clusters’ outer shells. Our findings provide strong evidence for the absence of the so called hydrodynamic expansions and for the dominance of Coulomb interactions in the explosion of the cluster nanoplasmas.

In this paper we present computational and theoretical studies of ex- treme multielectron ionization in Xen clusters (n = 55-2171, initial cluster radii R0 = 8.7-31.0 A) driven by ultraintense Gaussian infrared laser fields (peak intensity I M = 10 15 -10 20 W cm -2 , temporal pulse length τ = 10-100 fs, and frequency ν = 0.35fs -1 ). The microscopic approach, which rests on three sequential-parallel processes of in- ner ionization, nanoplasma formation, and outer ionization, properly describes the high ionization levels (with the formation of {Xe q+ }n with q = 5-36), the inner/outer cluster ionization mechanisms, and the nanoplasma response. The cluster size and laser intensity dependence of the inner ionization levels are determined by a com- plex superposition of laser-induced barrier suppression ionization (BSI), with the contributions of the inner field BSI manifesting ignition enhancement and screening retardation effects, together with electron impact ionization. The positively charged nanoplasma produced by inner ionization reveals intensity-dependent spatial inho- mogeneity and spatial anisotropy, and can be either persistent (at lower intensities) or transient (at higher intensities). The nanoplasma is depleted by outer ionization that was semiquantitatively described by the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity, and pulse length depen- dence of the outer ionization yield.

We present a molecular dynamics (MD) simulation code for the ex- ploration of extreme multielectron ionization and attosecond-femtosecond electron dynamics in elemental and molecular clusters driven by ultraintense (peak intensity IM = 10 15 -10 16 W cm -2 ), ultrafast (temporal pulse widths τ = 10-100 fs), near infrared (photon frequency 0.35 fs -1 ) laser fields. Validity conditions are presented for the applicability of classical MD simulations to high-energy electron dynamics, which rest on the localization of the wave packet and the distinguishability of identical particles. We also examine the cluster size domain for the applicability of the MD simulation code where the laser intensity is uniform inside the cluster.

Ultrafast cluster dynamics encompasses femtosecond nuclear dynamics, attosecond electron dynamics, and electron-nuclear dynamics in ultraintense laser fields (peak intensities 10 15 –10 20 W·cm −2 ). Extreme cluster multielectron ionization produces highly charged cluster ions, e.g., (C 4+ (D + ) 4 ) n and (D + I 22+ ) n at I M = 10 18 W·cm −2 , that undergo Coulomb explosion (CE) with the production of high-energy (5 keV to 1 MeV) ions, which can trigger nuclear reactions in an assembly of exploding clusters. The laser intensity and the cluster size dependence of the dynamics and energetics of CE of (D 2 ) n , (HT) n , (CD 4 ) n , (DI) n , (CD 3 I) n , and (CH 3 I) n clusters were explored by electrostatic models and molecular dynamics simulations, quantifying energetic driving effects, and kinematic run-over effects. The optimization of table-top dd nuclear fusion driven by CE of deuterium containing heteroclusters is realized for light-heavy heteroclusters of the largest size, which allows for the prevalence of cluster vertical ionization at the highest intensity of the laser field. We demonstrate a 7-orders-of-magnitude enhancement of the yield of dd nuclear fusion driven by CE of light-heavy heteroclusters as compared with (D 2 ) n clusters of the same size. Prospective applications for the attainment of table-top nucleosynthesis reactions, e.g., 12 C(P,γ) 13 N driven by CE of (CH 3 I) n clusters, were explored.

We advance an approach for the study of multistate dynamics of low Rydberg excitations in XeAr N /Xe*( 3 P 1 )Ar N /Xe + Ar N clusters on the time scale of nuclear motion, as explored by pump-probe neutral-to excited-to positive ion (NEEXPO) femtosecond spectroscopy. The dynamics of the Xe*Ar N ( N =54) cluster induced by charge expansion inferred from the calculation of NEEXPO signals at different probe energies, manifests the lifetime τ 1 ≃100 fs for the initial formation of the ‘bubble’, an intracluster vibrational energy redistribution (IVR) lifetime τ I/e ≃5.0 ps and an IVR completion time τ c ≃8–10 ps, which corresponds to the bubble equilibration.

The formation of positively charged antimony oxide clusters has been investigated as a function of oxygen partial pressure using time of flight mass spectrometry. With increasing oxygen partial pressure magic number patterns are observed, which can be attributed to the clusters of (Sb2O3)n+ and (Sb2O3)n(SbO)+ with 2⩽n

We present a theoretical study of the multistate dynamics of the Ag3 - /Ag3/Ag3 + system on the time scale of nuclear motion, as explored by femtosecond pump-probe negative ion-to neutral-to positive ion (NENEPO) spectroscopy. The dynamics of the Ag3 cluster initiated from its linear transition state involves configurational relaxation, intracluster collision, and onset of IVR, resonant and dissipative IVR and vibrational equilibration, whose time scales were determined. Our analysis reveals that theory is essential for the elucidation of the rich dynamic information regarding geometrical change, completion of IVR, and vibrational coherence effects in the NENEPO femtosecond signals.

We analyze spectral absorption line shapes simulated using the molecular dynamics spectral density method. We explore three classes of line shapes: (1) the region of the 0–0 S0→S1(ππ*) transition of perylene⋅ArN clusters, (2) the Xe1S0→3P1 transition of XeArN clusters, and (3) the photoelectron spectrum of the Li4F4 cluster in the valence region. These spectra represent examples for weak, unresolved, and extensive vibrational progressions, which have been analyzed and assigned. Employing a simplified model for the energy gap autocorrelation function allows for an understanding of the different behaviors and for a classification of the interrelation between nuclear dynamics and spectral line shapes. With decreasing the characteristic decay time of the transition dipole autocorrelation function, the line shape passes the limiting cases of the model in the order fast modulation limit→vibrational progression limit→slow modulation limit, with the vibrational progression limit extending the limiting cases of th...

In this paper we utilize the molecular dynamics spectral density method to explore the absorption line shapes of the ‘SO - 3P~(6s[3/2]1) electronic excitation of Xe in XeArN (N = 12-206) over the temperature range T = 10-40 K, with the Xe atom being located in distinct substitutional sites of the heterocluster (at T I 30 K), or in an interior position in nonrigid and in amorphous clusters. The Xe(’So-3Pl) extravalence excitations provide a sensitive microscopic probe for the local microenvironment of the Xe atom in these elemental clusters. The electronic excitations of Xe were described by the modified tight binding scheme (Webber, S.; Jortner, J.; Rice, S. A. J. Chem. Phys. 1965,42, 1907) with reliable Xe(3P~)-Ar(1So) excited-state exp-6 pair potentials (Messing, I.; Raz, B.; Jortner, J. J. Chem. Phys. 1977, 66, 2239). The site-specific and clustersize-dependent spectroscopic observables were characterized in terms of the blue spectral shift dv of the absorption band peak, the spectral line width (FWHM) r of the band, the spectral line shape, and their temperature dependence. The simulated spectra reveal an atomic shell structure with a hierarchy of Xe occupied site-specific spectral shifts decreasing in the order &(central site) > &(interior sites) > &(substitutional surface sites) > &(top atom), providing a spectroscopic method for the interrogation of the site-specific local structure. A quantification of the site specificity and the temperature dependence of BY was obtained in terms of its (nearly size invariant) exponential dependence on the average Xe- Ar nearest-neighbor distance, with the preexponential being proportional to the number of the nearest neighbors. We provided a spectroscopic identification of three temperature induced configurational changes in XeArN clusters, Le., a center surface dynamic isomerization of Xe in XeAr12 at T > 30 K, cluster configurational dilation around the central Xe atom in XeArN (N 2 54 with T 2 13 K for N = 54 and 35 K 130) clusters allowed for the identification of the Xe-occupied site-specific excitations of the central, interior and substitutional surface sites, while no evidence was obtained for the existence of the top atom site, which is precluded by surface melting. From the simulated temperature dependence of dv for the central site in large (N = 146-200) clusters, the cluster temperature was estimated to be T = 30-35 K. For XeArl2 we were able to identify the excitations of the center and surface sites at T = 30 K. Finally, the effects of nuclear dynamics on the spectra were inferred from the analysis of the power spectra of the energy gap correlation function, which established the dominance of the stochastic slow modulation limit for the line broadening.

We report on the calculations of kinetic energy distribution (KED) functions of multiply charged, high-energy ions in Coulomb explosion (CE) of an assembly of elemental Xe(n) clusters (average size (n) = 200-2171) driven by ultra-intense, near-infrared, Gaussian laser fields (peak intensities 10(15) - 4 × 10(16) W cm(-2), pulse lengths 65-230 fs). In this cluster size and pulse parameter domain, outer ionization is incomplete∕vertical, incomplete∕nonvertical, or complete∕nonvertical, with CE occurring in the presence of nanoplasma electrons. The KEDs were obtained from double averaging of single-trajectory molecular dynamics simulation ion kinetic energies. The KEDs were doubly averaged over a log-normal cluster size distribution and over the laser intensity distribution of a spatial Gaussian beam, which constitutes either a two-dimensional (2D) or a three-dimensional (3D) profile, with the 3D profile (when the cluster beam radius is larger than the Rayleigh length) usually being experimentally realized. The general features of the doubly averaged KEDs manifest the smearing out of the structure corresponding to the distribution of ion charges, a marked increase of the KEDs at very low energies due to the contribution from the persistent nanoplasma, a distortion of the KEDs and of the average energies toward lower energy values, and the appearance of long low-intensity high-energy tails caused by the admixture of contributions from large clusters by size averaging. The doubly averaged simulation results account reasonably well (within 30%) for the experimental data for the cluster-size dependence of the CE energetics and for its dependence on the laser pulse parameters, as well as for the anisotropy in the angular distribution of the energies of the Xe(q+) ions. Possible applications of this computational study include a control of the ion kinetic energies by the choice of the laser intensity profile (2D∕3D) in the laser-cluster interaction volume.

This chapter addresses some of the novel physical features of the response and dynamics of homonuclear and heteronuclear clusters in ultraintense laser fields, which pertain to new mechanisms of cluster extreme multi-electron ionization, the consequences of the interaction of an ultraintense laser with a spatially confined cluster, the dramatic effects of nuclear fusion driven by cluster Coulomb explosion, the implications of Coulomb instability of highly multicharged clusters, etc. Ultraintense table top lasers are characterized by a maximal intensity of ∼10 20 Wcm –2 , which constitutes the highest light intensity on the earth. Novel features of light–matter interactions emerge from the interaction of clusters with ultrashort and ultraintense laser fields. The modem research area of femtosecond cluster dynamics on the time scale of nuclear motion is transcended by moving toward attosecond–femtosecond electron dynamics in ultraintense laser fields. The response of clusters to ultraintense lasers induces well characterized ultrafast dynamics of electrons and of ions in these large finite systems.

The time resolved dynamics of diffusionless cube → ring isomerization of the Na4Cl4 cluster was interrogated by constant energy molecular dynamics simulations, utilizing the first passage time method. The nonreactive isomerization induced by nonselective vibrational excitation is well accounted for in terms of the statistical RRK theory, opening avenues for experimental exploration of time-resolved cluster isomerization dynamics.

Bismuth oxide cluster ions are reduced by propene in exactly the same way as solid bismuth oxide (Bi2 O3 ), which is used as a catalyst. Even in the case of the smallest bismuth oxide cluster ions, such as the Bi3 O4+ isomer shown in the picture, the supposedly unreactive bridging oxygen atom can participate in the alkene oxidation.

Based on trajectory calculations of xenon clusters up to ≈6000 atoms irradiated by laser pulses (peak intensities IM = 1014–1016 W cm−2, Gaussian pulse lengths τ = 10–230 fs and frequency 0.35 fs−1), we have analyzed the interrelation between outer ionization and ion kinetic energies. The following three main categories have been identified. (A) For short pulses (τ = 10 fs) of higher intensity IM = 1016 W cm−2, the outer ionization level leads to a sufficiently high positive cluster charge, which confines the remaining nanoplasma electrons to the cluster center. In this case, ion energies can be reasonably well accounted for by a multi-charge state lychee model, according to which outer ionization is vertical and the nanoplasma can be described by a non-expanding neutral cluster interior, causing a zero-energy component in the ion kinetic energy distribution and an expanding electron-free cluster periphery. (B) For a very low outer ionization level, which is realized for short pulses of low intensity (IM = 1014 W cm−2) and/or large clusters, a slow gradual evaporation of nanoplasma electrons under laser-free conditions on the picosecond time scale is observed, making the entire outer ionization process highly non-vertical despite the short laser pulse. Accordingly, ions are accelerated only by a gradual buildup of the total cluster charge. (C) For long pulses (τ = 230 fs), the cluster expansion during the laser pulse is large and outer ionization is non-vertical. The nanoplasma electrons attain high kinetic energies by resonance heating and are distributed over the entire ion framework without a neutral cluster interior. Consequently, a zero-energy component in the ion energy distribution is missing.