Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. IV. Coulomb explosion of molecular heteroclusters

A multifaceted application of designed coulomb explosion occurring on oxidized topological crystalline insulator SnTe

Multifaceted application of designed coulomb explosion process occurred on the SnTe@oxide experimental model.

A Coulomb explosion strategy to tailor the nano-architecture of α-MoO3 nanobelts and an insight into its intrinsic mechanism

Tailoring the nanoarchitecture of materials is significant for the development of nanoscience and nanotechnology. To date, one of the most powerful strategies is convergent electron beam irradiation (EBI). However, only two main functions of knock-on or atomic displacement have been achieved to date. In this study, a Coulomb explosion phenomenon was found to occur in α-MoO3 nanobelts (NBs) under electron beam irradiation, which was controllable and could be used to efficiently create nanostructures such as holes, gaps, and other atomic/nanometer patterns on a single α-MoO3 NB. Theoretical simulations starting from the charging state, charging rate to the threshold time of Coulomb explosion reveal that the Coulomb explosion phenomenon should result from positive charging. The results also show that the multiple charged regions are quickly fragmented, and the monolayered α-MoO3 pieces can then be peeled off once the Coulombic repulsion is sufficient to break the Mo-O bonds in the crystalline structure. It is believed that this efficient and versatile strategy may open up a new avenue to tailor α-MoO3 NBs or other kind of transition metal dichalcogenides via the Coulomb explosion effect.

Extreme ionization of Xe clusters driven by ultraintense laser fields

We applied theoretical models and molecular dynamics simulations to explore extreme multielectron ionization in Xe(n) clusters (n=2-2171, initial cluster radius R(0)=2.16-31.0 A) driven by ultraintense infrared Gaussian laser fields (peak intensity I(M)=10(15)-10(20) W cm(-2), temporal pulse length tau=10-100 fs, and frequency nu=0.35 fs(-1)). Cluster compound ionization was described by three processes of inner ionization, nanoplasma formation, and outer ionization. Inner ionization gives rise to high ionization levels (with the formation of [Xe(q+)](n) with q=2-36), which are amenable to experimental observation. The cluster size and laser intensity dependence of the inner ionization levels are induced by a superposition of barrier suppression ionization (BSI) and electron impact ionization (EII). The BSI was induced by a composite field involving the laser field and an inner field of the ions and electrons, which manifests ignition enhancement and screening retardation effects. EII was treated using experimental cross sections, with a proper account of sequential impact ionization. At the highest intensities (I(M)=10(18)-10(20) W cm(-2)) inner ionization is dominated by BSI. At lower intensities (I(M)=10(15)-10(16) W cm(-2)), where the nanoplasma is persistent, the EII contribution to the inner ionization yield is substantial. It increases with increasing the cluster size, exerts a marked effect on the increase of the [Xe(q+)](n) ionization level, is most pronounced in the cluster center, and manifests a marked increase with increasing the pulse length (i.e., becoming the dominant ionization channel (56%) for Xe(2171) at tau=100 fs). The EII yield and the ionization level enhancement decrease with increasing the laser intensity. The pulse length dependence of the EII yield at I(M)=10(15)-10(16) W cm(-2) establishes an ultraintense laser pulse length control mechanism of extreme ionization products.

Fragmentation channels of large multicharged clusters

We address unifying features of fragmentation channels driven by long-range Coulomb or pseudo-Coulomb forces in clusters, nuclei, droplets, and optical molasses. We studied the energetics, fragmentation patterns, and dynamics of multicharged (A+)n (n=55, 135, 321) clusters. In Morse clusters the variation of the range of the pair-potential induced changes in the cluster surface energy and in the fissibility parameter X=E(Coulomb)2E(surface). X was varied in the range of X=1-8 for short-range interactions and of X=0.1-1.0 for long-range interactions. Metastable cluster configurations were prepared by vertical ionization of the neutral clusters and by subsequent structural equilibration. The energetics of these metastable ionic clusters was described in terms of the liquid drop model, with the coefficients of the volume and surface energies depending linearly on the Morse band dissociation energy. Molecular-dynamics simulations established two distinct fragmentation patterns of multicharged clusters that involve cluster fission into a small number of large, multicharged clusters for X<1 and Coulomb explosion into a large number of individual ions and small ionic fragments for X>1. The Rayleigh instability limit X=1 separates between spatially anisotropic fission and spatially isotropic Coulomb explosion. Distinct features of the fragmentation energetics and dynamics were unveiled. For fission of n=55 clusters, large kinetic and internal energies of the large fragments are exhibited and the characteristic fragmentation time is approximately 700 fs, while for Coulomb explosion the major energy content of the small fragments involves kinetic energy and the characteristic fragmentation time of approximately 300 fs is shorter. The Rayleigh (X=1) limit, leading to isotropic Coulomb explosion, is transcended by a marked enhancement of the Coulomb energy, which is realized for extremely ionized clusters in ultraintense laser fields, or by a dramatic reduction of the surface energy as is the case for the expansion of optical molasses.

Tabletop nucleosynthesis driven by cluster Coulomb explosion

Coulomb explosion of completely ionized (CH4)n, (NH3)n, and (H2O)n clusters will drive tabletop nuclear reactions of protons with 12C6+, 14N7+, and 16O8+ nuclei, extending the realm of nuclear reactions driven by ultraintense laser-heterocluster interaction. The realization for nucleosynthesis in exploding cluster beams requires complete electron stripping from the clusters (at laser intensities I(M) > or = 10(19) W cm(-2)), the utilization of nanodroplets of radius 300-700 A for vertical ionization, and the attainment of the highest energies for the nuclei (i.e., approximately 30 MeV for heavy nuclei and approximately 3 MeV for protons).

Cluster dynamics transcending chemical dynamics toward nuclear fusion

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,gamma)(13)N driven by CE of (CH(3)I)(n) clusters, were explored.

REFLECTIONS ON PHYSICAL CHEMISTRY: Science and Scientists

▪ Abstract  This is the story of a young person who grew up in Tel-Aviv during the period of the establishment of the State of Israel and was inspired to become a physical chemist by the cultural environment, by the excellent high-school education, and by having been trained by some outstanding scientists at the Hebrew University of Jerusalem and, subsequently, by the intellectual environment and high-quality scientific endeavor at the University of Chicago. Since serving as the first chairman of the Chemistry Department of the newly formed Tel-Aviv University he has been immersed in research, in the training of young scientists, and in intensive and extensive international scientific collaboration. Together with the members of his “scientific family” he has explored the phenomena of energy acquisition, storage and disposal and structure-dynamics-function relations in large molecules, condensed phase, clusters and biomolecules, and is looking forward to many future adventures in physical chemistry.

“What to leave out and what to put in? That's the problem.” Hugh Lofting, Doctor Dolittle's Zoo, 1925

Dynamic acceleration effects in explosions of laser-irradiated heteronuclear clusters

Intense, femtosecond irradiation of atomic and molecular clusters can initiate Coulomb explosions, generating particle energies sufficient to drive nuclear fusion. Last and Jortner have proposed, based on particle dynamics simulations, that heteronuclear clusters with a mixture of heavy and light ions will not explode by the simple, equilibrium Coulomb model but that dynamic effects can lead to a boosting of energy of the lighter ejected ions [Phys. Rev. Lett. 87, 033401 (2001)]. We present experimental confirmation of this theoretically predicted ion energy enhancement in methane clusters.

Regular multicharged transient soft matter in Coulomb explosion of heteroclusters

Nanointerfaces of mobile, thin spherical shells of light ions that expand on the femtosecond time scale, can be produced by Coulomb explosion of extremely ionized molecular heteroclusters consisting of light and heavy ions, e.g., (D+Iq+)n (q = 7-35), which are generated in ultraintense laser fields (intensity, I, = 10(16) to 10(20) W.cm(-2)). Modeling, together with molecular dynamics simulations, reveals the expansion of 2D monolayers with high energies and narrow energy distributions [e.g., Eav approximately 23 keV and DeltaE/Eav = 0.16 for D+ from (D+I25+)(2171)] arising from kinematic run-over effects. The expanding regular, monoionic, spherical nanointerfaces manifest the attainment of transient self-organization in complex systems driven by repulsive Coulomb interactions.