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Coulomb explosion experiments using linearly polarized intense 60 fs laser pulses were conducted for structural characterization of three dichloroethylene (DCE) isomers, 1,1-DCE, cis-1,2-DCE, and trans-1,2-DCE. Under relatively low laser intensity at 1.8 × 1014 W/cm2, mass-resolved momentum imaging (MRMI) for selected fragment ions of 35Cl+ and C2+ revealed different patterns for the three isomers. The C2+ ion fragmented from multiply charged trans-1,2-DCE was forced to leave perpendicularly to the direction of the laser polarization, due to recoil forces from adjacent cations. In contrast, the fast ions of C2+ from cis-1,2-DCE exhibited an isotropic distribution, whereas the fast ions of C2+ from 1,1-DCE recoiled along the laser polarization together with the slow C2+ ions, and thereby distinction of the three isomers was demonstrated. Coulomb explosion occurs predominantly at specific orientation, which is useful for potential applications of MRMI analysis to molecular structure assays. [ABSTRACT FROM AUTHOR]

The behavior of nitrosyl chloride (ClNO) exposed to ionizing radiation was studied by direct probing valence-shell electrons in temporal coincidence with ions originating from the fragmentation process of the transient ClNO2+. Such a molecular dication was produced by double photoionization with synchrotron radiation in the 24–70 eV photon energy range. The experiment has been conducted at the Elettra Synchrotron Facility of Basovizza (Trieste, Italy) using a light beam linearly polarized with the direction of the polarization vector parallel to the ClNO molecular beam axis. ClNO molecules crossing the photon beam at right angles in the scattering region are generated by effusive expansion and randomly oriented. The threshold energy for the double ionization of ClNO (30.1 ± 0.1 eV) and six dissociation channels producing NO+/Cl+, N+/Cl+, N+/O+, O+/Cl+, ClN+/O+, NO+/Cl2+ ion pairs, with their relative abundance and threshold energies, have been measured.

The laser energy per unit surface, necessary to trigger material removal, decreases with the pulse shortening, becoming pulse–time independent in the sub-picosecond range. These pulses are shorter than the electron-to-ion energy transfer time and electronic heat conduction time, minimising the energy losses. Electrons receiving an energy larger than the threshold drag the ions off the surface in the mode of electrostatic ablation. We show that a pulse shorter than the ion period (Shorter-the-Limit (StL)) ejects conduction electrons with an energy larger than the work function (from a metal), leaving the bare ions immobile in a few atomic layers. Electron emission is followed by the bare ion’s explosion, ablation, and THz radiation from the expanding plasma. We compare this phenomenon to the classic photo effect and nanocluster Coulomb explosions, and show differences and consider possibilities for detecting new modes of ablation experimentally via emitted THz radiation. We also consider the applications of high-precision nano-machining with this low intensity irradiation.

We consider the dust charging processes in protoplanetary disks. It is shown that in the atmosphere of a disk, grains can acquire anomalously high positive charges, which can lead to their destruction as a result of the Coulomb explosion. The charging is due to the combined effect of radiation from a protostar and of electron and ion currents from the surrounding plasma. For typical protoplanetary disk conditions, such a process turns out to be effective both for porous dust grains of micron sizes and for submicron crystalline grains. Critical charges that are necessary for the destruction of dust grains and the charges acquired by the particles are found for their different sizes and various parameters of the dusty plasmas. Critical grain sizes as functions of the distance to the host star are calculated. It is shown that the Coulomb explosion leads to the appearance of a cascade of crushing of large dust grains. The character of the dependence of crushing conditions on the dust particle radius can lead to the formation of a bimodal grain size distribution in some areas of protoplanetary disks. One fraction corresponds to large particles that are not subject to destruction and the other, to small particles of submicron size. [ABSTRACT FROM AUTHOR]

We investigated the ultrafast proton migration and the Coulomb explosion (CE) dynamics of methyl chloride (CH3Cl) in intense femtosecond laser fields at thewavelengths of 800 nm (5.5 x 1014 W/cm2) and 400 nm (4 x 1014W/cm2), respectively. Various fragment channels from molecular dication and trication were observed by coincidence momentum imaging through the measurement of their kinetic energy releases (KERs). The proton migration from different charged parent ions was analyzed from the obtained KER distributions. For the direct CE channel of CH3+ + Cl+ and CH3+ + Cl2+, the contribution of multiply excited electronic states and multicharged states is identified. In addition, the measurements of relative yields of the fragmentation channel at different laser wavelengths provide a selective control of proton migration for CH3Cl molecules in intense laser fields. [ABSTRACT FROM AUTHOR]

In this work we instigated the fragmentation of Au microparticles supported on a thin amorphous carbon film by irradiating them with a gradually convergent electron beam inside the Transmission Electron Microscope. This phenomenon has been generically labeled as "electron beam-induced fragmentation" or EBIF and its physical origin remains contested. On the one hand, EBIF has been primarily characterized as a consequence of beam-induced heating. On the other, EBIF has been attributed to beam-induced charging eventually leading to Coulomb explosion. To test the feasibility of the charging framework for EBIF, we instigated the fragmentation of Au particles under two different experimental conditions. First, with the magnetic objective lens of the microscope operating at full capacity, i.e. background magnetic field B = 2 T, and with the magnetic objective lens switched off (Lorenz mode), i.e. B = 0 T. We observe that the presence or absence of the magnetic field noticeably affects the critical current density at which EBIF occurs. This strongly suggests that magnetic field effects play a crucial role in instigating EBIF on the microparticles. The dependence of the value of the critical current density on the absence or presence of an ambient magnetic field cannot be accounted for by the beam-induced heating model. Consequently, this work presents robust experimental evidence suggesting that Coulomb explosion driven by electrostatic charging is the root cause of EBIF. [Display omitted] • Experimental study of the magnetic field effect on the e-beam induced fragmentation • Theoretical framework explaining the difference of critical current densities • The simulated Coulomb explosion occuring in pico-second order • Raman, XRD, SAED studies of the amorphous carbon films and 4-probe resistance measurements [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the dissociative photoionization of CHBrCl2 molecules in a femtosecond laser field by time-of-flight mass spectrum and dc-slice imaging technology. The results suggest that the low kinetic energy components are from the dissociative ionization process of single-charged molecular ions. The angular distribution of fragment Cl+ ions can be attributed to the features of dissociative state and molecular configuration, and that of Br+ ions results from the electronic wave-packet evolution and combination of the multi-dissociation processes. The high kinetic energy components are from the Coulomb explosion of multi-charged molecular ions, and the error of the C-Br distance involved in the Coulomb explosion can be explained by the movement of the effective charge center of the polyatomic molecule. [ABSTRACT FROM AUTHOR]

Nanoparticle mediated laser induced breakdown can be used for Nanoparticle synthesis, cell nanosurgery and laser induced breakdown spectroscopy. To investigate the photo-thermal conversion of gold nanoparticles during pulsed laser irradiation, the electron-phonon two temperature model was established in this study. The impact of laser energy density and pulse width on the thermal conversion and morphology change of gold nanorods were investigated and compared with experimental observations. The results show that the melting threshold of gold nanorods under nanosecond laser irradiation is about twenty times that of femtosecond laser irradiation. The mechanisms of nanorod fragmentation are different between femto and nanosecond laser irradiation: particle melting is more likely to occur in nanosecond laser irradiation, while the Coulomb explosion is highly likely to occur in femtosecond laser irradiation. [ABSTRACT FROM AUTHOR]

Fixing molecules in space is a crucial step for the imaging of molecular structure and dynamics. Here, we demonstrate three-dimensional (3D) field-free alignment of the prototypical asymmetric top molecule indole using elliptically polarized, shaped, off-resonant laser pulses. A truncated laser pulse is produced using a combination of extreme linear chirping and controlled phase and amplitude shaping using a spatial-light-modulator (SLM) based pulse shaper of a broadband laser pulse. The angular confinement is detected through velocity-map imaging of H+ and C2+ fragments resulting from strong-field ionization and Coulomb explosion of the aligned molecules by intense femtosecond laser pulses. The achieved three-dimensional alignment is characterized by comparing the result of ion-velocity-map measurements for different alignment directions and for different times during and after the alignment laser pulse to accurate computational results. The achieved strong three-dimensional field-free alignment of < cos 2 δ > = 0.89 demonstrates the feasibility of both, strong three-dimensional alignment of generic complex molecules and its quantitative characterization. Field-free 3D alignment of complex molecules is an important step toward the imaging of molecular dynamics. Here, the authors demonstrate pulse-shaping of long picosecond pulses for the 3D field-free alignment of the prototypical non-rotation-symmetric molecule indole. [ABSTRACT FROM AUTHOR]

We report on the design and capabilities of a reaction microscope (REMI) end-station at the Shanghai Soft X-ray Free-Electron Laser Facility (SXFEL). This apparatus allows high-resolution and 4 π solid-angle coincidence detection of ions and electrons. The components of REMI, including a supersonic gas injection system, spectrometer, detectors and data acquisition system, are described in detail. By measuring the time of flight and the impact positions of ions and electrons on the corresponding detectors, three-dimensional momentum vectors can be reconstructed to study specific reaction processes. Momentum resolutions of ions and electrons with 0.11 a.u. are achieved, which have been measured from a single ionization experiment of oxygen molecules in an infrared (IR), femtosecond laser field, under vacuum at 1.2 × 10 − 10 torr, in a reaction chamber. As a demonstration, a Coulomb explosion experiment of oxygen molecules in the IR field is presented. These results demonstrate the performance of this setup, which provides a basic tool for the study of atomic and molecular reactions at SXFEL. [ABSTRACT FROM AUTHOR]

A theoretical model of laser-induced ion acceleration during the Coulomb explosion of a flat uniform target with two-component ion composition is presented. To the difference from existing models, here, the case of an arbitrary ratio between the total charges of the ion components is considered. Comparison of the result with the numerical solution shows good agreement almost in the entire range of controlling parameters, which allows one to optimize the considered regime of ion acceleration. To this end, conditions were determined for the generation of beams of the best quality. [ABSTRACT FROM AUTHOR]

Coulomb explosion, characterized by Coulomb repulsion between particles with the same charge on the surface of a material, has been used to realize exquisite nano-manipulation, however, researchers usually found only one aspect of the application of Coulomb explosion when they utilized it. Herein, we successfully design a "metal@insulator" based Coulomb explosion process by irradiating oxidized topological crystalline insulator SnTe under an electron beam. The occurrence of Coulomb explosion mainly due to the oxide-encapsulated SnTe retained the metallic surface state, which not only can be positively charged but also can realize charge accumulation through the shielding effect of the insulating oxide layer. By changing experimental conditions and carefully studying various experimental phenomena, we conclude six aspects of the application, namely, speculating the metallic surface state of the oxide-encapsulated SnTe, controllable fabricating nanoplates, observing the PVD (physical vapor deposition) process under low temperature, rapid coating film, unraveling the oriented attachment and self-recrystallization of larger nanocrystals and fabricating hollow structure. Our findings are important for utilizing Coulomb explosion as well as other EBI techniques to conduct nano-manipulation. [ABSTRACT FROM AUTHOR]

We present the results of an integrated laboratory and modeling investigation into the impact of stellar X-rays on cosmic dust. Carbonaceous grains were prepared in a cooled (<200 K) supersonic expansion from aromatic molecular precursors, and were later irradiated with 970 eV X-rays. Silicate (enstatite) grains were prepared via laser ablation, thermally annealed, and later irradiated with 500 eV X-rays. Infrared spectra of the 3.4 ÎĽ m band of the carbon sample prepared with benzene revealed 84% ± 5% band area loss for an X-ray dose of 5.2 Ă—1023 eV.cmâˆ'2. Infrared spectra of the 8â€"12 ÎĽ m Siâ€"O band of the silicate sample revealed band area loss up to 63% ± 5% for doses of 2.3 Ă— 1023 eV.cmâˆ'2. A hybrid Monte Carlo particle trajectory approach was used to model the impact of X-rays and ensuing photoelectrons, Auger and collisionally ionized electrons through the bulk. As a result of X-ray ionization and ensuing Coulomb explosions on surface molecules, the calculated mass loss is 60% for the carbonaceous sample and 46% for the silicate sample, within a factor of 2 of the IR band loss, supporting an X-ray induced mass-loss mechanism. We apply the laboratory X-ray destruction rates to estimate the lifetimes of dust grains in protoplanetary disks surrounding 1 M ⊙ and 0.1 M ⊙ G and M stars. In both cases, X-ray destruction timescales are short (a few million years) at the disk surface, but are found to be much longer than typical disk lifetimes (≳10 Myr) over the disk bulk. [ABSTRACT FROM AUTHOR]

We discuss how Coulomb explosion imaging (CEI), triggered by intense femtosecond laser pulses and combined with laser-induced alignment and covariance analysis of the angular distributions of the recoiling fragment ions, provides new opportunities for imaging the structures of molecules and molecular complexes. First, focusing on gas phase molecules, we show how the periodic torsional motion of halogenated biphenyl molecules can be measured in real time by timed CEI, and how CEI of one-dimensionally aligned difluoroiodobenzene molecules can uniquely identify four structural isomers. Next, focusing on molecular complexes formed inside He nano-droplets, we show that the conformations of noncovalently bound dimers or trimers, aligned in one or three dimensions, can be determined by CEI. Results presented for homodimers of CS2, OCS, and bromobenzene pave the way for femtosecond time-resolved structure imaging of molecules undergoing bimolecular interactions and ultimately chemical reactions. [ABSTRACT FROM AUTHOR]

The angular distribution of the ions coming from Coulomb explosion following femtosecond ionisation of methyl iodide is studied in the spectral range of 600 to 1450 nm. Under these conditions, iodine and methyl fragment ions are generated, both via dissociative ionisation and via Coulomb explosion following the double ionisation of the parent ion. However, the dependence of the angular distribution of the fragment ions on the ionisation wavelength is completely different for those two mechanisms: dissociative ionisation fragments are being ejected with high anisotropy, irrespectively of the wavelength, while the angular distribution of the Coulomb explosion fragments changes from anisotropic, for an excitation wavelength close to 600 nm, to isotropic close to 950 nm, and remain isotropic up to 1450 nm. [ABSTRACT FROM AUTHOR]

Coupling covariance map analysis with ultrafast laser-induced Coulomb explosion imaging (CEI) enabled us to characterise the dissociative ionisation dynamics of methoxycarbonylsulfenyl chloride (H3COCOSCl). We applied a 3D multi-coincidence detection technique which is necessary for covariance imaging analysis. With the aid of such analysis, we found meaningful correlations between several product ion pairs that revealed different fragmentation channels. A weak, narrow correlation in the covariance image of H3COC(O)+/Cl+ was assigned to a concerted three-body dissociation channel. We also observed a broadly distributed correlation in the covariance image of COS+/HCO+, which is ascribed to a multi-body fragmentation channel. Ab initio calculations were carried out to determine the likely starting structures. A very sharp feature in the covariance image of Cl+/ CH3+ indicated that this pair of ions is produced from a two-body-like fragmentation event of CH3Cl2+. We show by direct comparison with CEI of CH3Cl that, contrary to a previously suggested assignment, this ion pair is produced from CH3Cl, which is formed either in the bubbler or gas line before the molecular beam interacts with the laser beam. [ABSTRACT FROM AUTHOR]

We present a time-resolved analysis of Rayleigh scattering measurements to determine the average size of methane clusters and find the optimum timing for laser-cluster fusion experiments. We measure Rayleigh scattering and determine the average size of methane clusters varying the backing pressure (P0) from 11 bar to 69 bar. Regarding the onset of clustering, we estimate that the average size of methane clusters at the onset of clustering is Nc0≅20 at 11 bar. According to our measurements, the average cluster radius r follows the power law of r∝P01.86. Our ion time-of-flight measurements indicate that we have produced energetic deuterium ions with kT = 52±2 keV after laser-cluster interaction using CD4 gas at 50 bar. We find that this ion temperature agrees with the predicted temperature from CD4 clusters at 50 bar with r = 14 nm assuming the Coulomb explosion model. [ABSTRACT FROM AUTHOR]

In this paper, we present an experimental study of charge propensities formed when Argon clusters are ionized with laser pulses of intensities up to 4 × 10 18 Wcm - 2 . The mean cluster size is varied from 1400 to 36,500 atoms to probe changes in ionization propensity at a given laser intensity. We attempted to use the Uniform charge scheme (that was earlier successful in fitting the ion energy spectra) to fit the ion charge state histograms. The difficulty in fitting the measured charge histograms compel us to adopt a non-uniform charging scheme to fit the measured ion charge propensity. Three different empirical weight functions that represent the charge of atoms in different shells of the cluster are used. The parameters of the empirical functions are optimized by least square fit to match the measured ion kinetic energy spectra. The weight function represents the terminal charge states of the ions coulomb exploded from the cluster and gives a better insight into the Coulomb explosion of the charged nanosphere. [ABSTRACT FROM AUTHOR]

The laser intensity dependence of the recoil energies from the Coulomb explosion of small argon clusters has been investigated by resolving the contributions of the individual charge states to the ion recoil energy spectra. Between 10 14 and 10 15 W/cm 2 , the high-energy tail of the ion energy spectra changes its shape and develops into the well-known knee feature, which results from the cluster size distribution, laser focal averaging, and ionization saturation. Resolving the contributions of the different charge states to the recoil energies, the experimental data reveal that the basic assumption of an exploding homogeneously charged sphere cannot be maintained in general. In fact, the energy spectra of the high-q show distinct gaps in the yields at low kinetic energies, which hints at more complex radial ion charge distributions developing during the laser pulse impact. [ABSTRACT FROM AUTHOR]

It was recently shown that nanostructured targets with largely spaced gold ultrasmall nanoparticles (NPs) show outstanding performances in enhancing the laser-driven ions' acceleration process due to the higher laser-to-target energy absorption [Vallières et al., Phys. Rev. Accel. Beams 22, 091303 (2019)]. Based on this structure, here, an alternative nanostructured design is proposed to promote light/heavy ions' acceleration quality. The scheme relies on using a gold NP layered nanosphere filled with a low-density argon gas. The nanosphere has an inner layer of vanadium and an outer layer of proton–carbon (1:1) mixture. The validity of this suggestion has been simulated by the two-dimensional particle-in-cell code (EPOCH). Simulation results indicate that the interaction of ultra-intense laser (∼ 4.61 × 1019 W/cm2) with a gas-filled gold NP layered nanosphere can positively decrease the aggregation of electrons stated inside the target, leading to higher Coulomb repulsion between charged ions. Therefore, we can expect the generation of quasi-monoenergetic H+, C6+, V20+, and Au49+, as well as Ar15+ (cutoff energy of ∼ 0.49 MeV/u and relative divergence angle of 2.9°) at the end of the interaction. From simulations, as the interaction terminates, for a gas-filled gold NP layered nanosphere with an optimal gap space of 80 nm, a cutoff energy increase of roughly 19% for H+, 16.4% for C6+, and rather equal percent of 15.9% for medium-heavy ions (V20+ and Au49+) is obtained with respect to a hollow gold NP layered nanosphere. Moreover, a relative divergence angle decrease of up to nearly 0.29–1.91 times will be calculated for the accelerated ions. Overall, the results verify that a gas-filled gold NP layered nanosphere can be regarded as a candidate for the generation of quasi-monoenergetic ions through the spherical Coulomb explosion regime. [ABSTRACT FROM AUTHOR]

We investigate the fragmentation of the CH4 cluster by fast electron impact at stagnation pressures from 0.5 bar to 16 bar. By measuring the time of flight spectrum (TOF), two types of ions, including (CH4)n−1CH5+ and (CH4)n−2(C2Hm)+, are observed. In the 1D TOF spectrum, it is shown that for the stagnation pressure larger than 4 bar, the former ion is predominant for each n, similar to the previous experimental result. However, as the pressure decreases to 0.5 or 2 bar, the contribution of the C2Hm+ ion is dominant over that of the CH4CH5+ ion. In the 2D coincident TOF spectrum, the above two patterns of ions are also distinguished, and the enhancement of C2Hm+ is observed at 4 bar pressure. The phenomena appearing in 2D and 1D TOF spectra imply that the C2Hm+ ion prefers to survive in a smaller cluster, while the stabilization of the protonated ion needs a more massive cluster environment.

Additive manufacturing (AM) will empower the next breakthroughs in nanotechnology by combining unmatched geometrical freedom with nanometric resolution. Despite recent advances, no micro-AM technique has been able to synthesize functional nanostructures with excellent metal quality and sub-100 nm resolution. Here, significant breakthroughs in electrohydrodynamic redox 3D printing (EHD-RP) are reported by directly fabricating high-purity Cu (>98 at.%) with adjustable voxel size from >6µm down to 50 nm. This unique tunability of the feature size is achieved by managing in-flight solvent evaporation of the ion-loaded droplet to either trigger or prevent the Coulomb explosion. In the first case, the landing of confined droplets on the substrate allows the fabrication of high-aspect-ratio 50 nm-wide nanopillars, while in the second, droplet disintegration leads to large-area spray deposition. It is discussed that the reported pillar width corresponds to the ultimate resolution achievable by EHD printing. The unrivaled feature size and growth rate (>100 voxel s -1 ) enable the direct manufacturing of 30 µm-tall atom probe tomography (APT) tips that unveil the pristine microstructure and chemistry of the deposit. This method opens up prospects for the development of novel materials for 3D nano-printing., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

The fragmentations of iodine cyanide ions created with 2 to 8 positive charges by photoionization from inner shells with binding energies from 59 eV (I 4d) to ca. 900 eV (I 3p) have been examined by multi-electron and multi-ion coincidence spectroscopy with velocity map imaging ion capability. The charge distributions produced by hole formation in each shell are characterised and systematic effects of the number of charges and of initial charge localisation are found. [ABSTRACT FROM AUTHOR]

We apply a three-fold covariance imaging method to analyse previously acquired data [C. S. Slater et al., Phys. Rev. A 89, 011401(R) (2014)] on the femtosecond laser-induced Coulomb explosion of spatially pre-aligned 3,5-dibromo-3',5'-difluoro-4'-cyanobiphenyl molecules. The data were acquired using the "Pixel Imaging Mass Spectrometry" camera. We show how three-fold covariance imaging of ionic photofragment recoil trajectories can be used to provide new information about the parent ion's molecular structure prior to its Coulomb explosion. In particular, we show how the analysis may be used to obtain information about molecular conformation and provide an alternative route for enantiomer determination. [ABSTRACT FROM AUTHOR]

Twin graphene can introduce stable and extended defects to energy band engineering, giving unique electron transport properties, which is expected to have potential applications in the fields of magnetism, spin transport or photoluminescence. This study proposes a method of using electric-field-assisted temporally-shaped femtosecond laser ablation liquid (ETLAL) of graphene dispersion to prepare graphene quantum dots (GQDs) with an average particle size of 2–3 nm and oxygen-containing functional groups modified surface, which realizes the controllable preparation of single crystal and twin GQDs (5-fold twin). This method controls the crystallinity of GQDs from two aspects: (1) The intervention of an electric field can rapidly command the directional motion of the cavitation bubbles and the nanoparticles contained therein to collide and crystallize at higher temperatures and pressures, which is the key to the formation of twin GQD; (2) Adjusting temporally-shaped femtosecond laser pulse delay could control the proportion of the Coulomb explosion during the ablation process, which increases the carbon cluster supplied by the cavitation bubble which is the key of polyploid number in twin GQDs. This research provides a fast, green strategy for the preparation of unprecedented twin GQDs, which is of great significance to the applications in the field of 2D material defect engineering. [Display omitted] [ABSTRACT FROM AUTHOR]

Coulomb explosion imaging is a promising experimental tool to study individual molecules. In this work simulation data for the x-ray induced Coulomb explosion of 2-iodopyridine is analyzed and the involved fragmentation dynamics are described. It is found that particular final ion momenta show correlations that reflect a collision of two atoms during the explosion. Variations of the proton kinetic energies can be associated with variations in the charge build-up time. Covariances of the forces during the explosion can be utilized to simplify the description of the dynamics in reduced dimensionality using only four collective coordinates. [ABSTRACT FROM AUTHOR]

Using single-shot velocity map imaging technique, explosion imaging of different ion species ejected from 50 nm SiO2 nanoparticles are obtained excitedly by strong near-infrared and ultraviolet femtosecond laser fields. Characteristic momentum distributions showing forward emission of the ions at low excitation intensities and shock wave behaviors at high intensities are observed. When the excitation intensity is close to the dissociative ionization threshold of the surface molecules, the resulting ion products can be used to image the instant near-field distributions. The underlying dynamics of shock formation are simulated by using a Coulomb explosion model. Our results allow one to distinguish the ultrafast strong-field response of various molecular species in nanosystems and will open a new way for further exploration of the underlying dynamics of laser-and-nanoparticle interactions. [ABSTRACT FROM AUTHOR]

We have deduced the structure of the bromobenzeneâ€"I2 heterodimer and the (bromobenzene)2 homodimer inside helium droplets using a combination of laser-induced alignment, Coulomb explosion imaging (CEI), and three-dimensional ion imaging. The complexes were fixed in a variety of orientations in the laboratory frame, then in each case multiply ionized by an intense laser pulse. A three dimensional ion imaging detector, including a Tpx3Cam detector allowed us to measure the correlations between velocity vectors of different fragments and, in conjunction with classical simulations, work backward to the initial structure of the complex prior to explosion. For the heterodimer, we find that the I2 molecular axis intersects the phenyl ring of the bromobenzene approximately perpendicularly. The homodimer has a stacked parallel structure, with the two bromine atoms pointing in opposite directions. These results illustrate the ability of CEI to determine the structure of large complexes, and point the way toward real-time measurements of bimolecular reactions inside helium droplets. [ABSTRACT FROM AUTHOR]

Abstract The trihydrogen ion has a central role in creating complex molecules in the interstellar medium. Therefore, its formation and destruction mechanisms in high photon energy environments involving organic molecules are drawing significant experimental and theoretical attention. Here, we employ a combination of time‐resolved ultrafast extreme‐ultraviolet pump and near‐infrared probe spectroscopy applied to the deuterated CH3OD methanol molecule. Similar to other double‐ionization studies, the isotopic labeling reveals two competing pathways for forming trihydrogen: A) H3++COH+ and B) H3++HCO+. We validate our high‐level ab initio nonadiabatic molecular dynamic simulations by showing that it closely reproduces the essential features of the measured kinetic energy release distribution and branching ratios of the two pathways of the deuterated system. The success of ab initio simulation in describing single photon double‐ionization allows for an unprecedented peek into the formation pathways for the undeuterated species, beyond present experimental reach. For this case, we find that the kinetic energy release of pathway B shifts to lower energies by more than 0.6 eV due to a dynamical isotope effect. We also determine the mechanism for trihydrogen formation from excited states of the dication and elucidate the isotope effect's role in the observed dynamics.

Fragmentation processes of SO2 following excitation of the six main O 1s pre-edge resonances, as well as above the ionization threshold and below the resonances, are studied using a position-sensitive time-of-flight ion imaging detector, and the associated dissociation branching ratios and break-up dynamics are determined. In order to distinguish between the O+ and S2+ fragments of equal mass-to-charge ratio, the measurements have been performed with the isotopically enriched S18O² sample. By analysis of the complete set of the fragment momentum vectors, the β values for the fragments originating from the SO+ + O+ break-up and the kinetic energy release for fragmentation channels of both SO22+ and SO23+ parent ions are determined. We also present results on the three-body break-up dynamics. [ABSTRACT FROM AUTHOR]

The interaction of the sub-picosecond UV laser in sub-relativistic intensities with deuterium is investigated. At high plasma temperatures, based on the quantum correction in the collision frequency, the electron heating and the ion block generation in plasma are studied. It is found that due to the quantum correction, the electron heating increases considerably and the electron temperature uniformly reaches up to the maximum value of 4.91×107 K. Considering the quantum correction, the electron temperature at the laser initial coupling stage is improved more than 66.55% of the amount achieved in the classical model. As a consequence, by the modified collision frequency, the ion block is accelerated quicker with higher maximum velocity in comparison with the one by the classical collision frequency. This study proves the necessity of considering a quantum mechanical correction in the collision frequency at high plasma temperatures. [ABSTRACT FROM AUTHOR]

Dissociative ionization dynamics were studied experimentally for CO2 driven by intense laser pulses. Three-dimensional momentum vectors of correlated atomic ions were obtained for each three-body fragmentation event using triple ion coincidence measurement. Newton diagram demonstrated that three-body fragmentation of CO2n+ (n = 3-6) can occur through Coulomb explosion process and sequential fragmentation process depending on the fragmentation channels. The experimental data from these two processes were disentangled by using correlation diagram of correlated ions. Based on the accurate Coulomb explosion data, we reconstructed the bond angle distributions of CO2n+ at the moment of fragmentation, which are close to that of neutral CO2 before laser irradiation. [ABSTRACT FROM AUTHOR]

In this paper, an improved three-dimensional two-temperature model for multi-pulse femtosecond laser ablation of aluminum was proposed and proved in our experiment. Aiming to achieve hole-drilling with a high ratio of depth/entrance diameter in vacuum, this model can predict the depth and radius of the drilled holes precisely when employing different laser parameters. Additionally, for multi-pulse laser ablation, we found that the laser fluence and number of pulses are the dominant parameters and the multi-pulse ablation threshold is much lower than the single-pulse one, which will help to obtain high-quality holes. [ABSTRACT FROM AUTHOR]

With the development of femtosecond (fs) laser technology, an fs laser pulse with 10s of Joule, even 100s of Joule energy is available and the focused laser intensity can be expected to induce the pure Coulomb explosion of the cluster with a much larger average radius than before. Meanwhile, the production of gas cluster with an average radius of upto 10s of nanometer has been possible. In this case, it is necessary to reinvestigate the feasibility of 109 n/shot neutron yield for the practical application in the intense fs laser-driven nuclear fusion. In this work, the neutron yield from the explosions of the D2 clusters of 6–20 nm average radius at the 0.5–100 J pulse energy and the CD4 clusters was investigated theoretically. It is found that the optimum neutron yield of 109 n/shot can be obtained at the laser energy and the cluster radius currently available. However, a clustered-gas jet with a large cross-section is demanded to match the proper plasma diameter. [ABSTRACT FROM AUTHOR]

We demonstrate that by combining two robust theoretical quantum chemistry calculation techniques, stepwise ionization of C60 fullerene by UV and extreme UV photons can in principle occur up to a limit as high as C6026+ before coulomb explosion of the cage. Furthermore, these highly ionized forms exhibit a comparable structural and bonding stability as for the neutral fullerene. Certain astrophysical sources like the central stars of planetary nebulae and the hottest white dwarf stars have sufficiently hard UV radiation fields that can result in a series of highly charged C60q+ species from q = 1 up to q = 16. Harsher environments, like hot X-ray bubbles in planetary nebulae, X-ray binaries and other sources, may further push the ionization right up to the q = 26 limit. These remarkable theoretical findings add new avenues to complex ion/molecule reactions, the chemistry of fragmentation products and additional pathways for spreading carbon throughout the universe. The implications for the emerging field of astrochemistry of C60 fullerene in all its possible states could be profound. [ABSTRACT FROM AUTHOR]

We report the comprehensive measurement of the Coulomb explosion of the double and triple ionization of N2 in collisions with slow highly-charged ions. The experiments are carried out with ion beams of different charge states for a given velocity (1 a.u.) and at three different velocities for a given charge state (O6+). By analyzing the kinetic energy release distributions of and molecular ions, the effects of projectile velocity and charge state on the population of different molecular states are inferred. We explain such a systematic variation in the population of different molecular states considering the energy deposition to N2 by the projectile ions. [ABSTRACT FROM AUTHOR]

The Jahn-Teller effect is an essential mechanism of spontaneous symmetry breaking in molecular and solid state systems, and has far-reaching consequences in many fields. Up to now, to directly image the onset of Jahn-Teller symmetry breaking remains unreached. Here we employ ultrafast ion-coincidence Coulomb explosion imaging with sub-10 fs resolution and unambiguously image the ultrafast dynamics of Jahn-Teller deformations of CH 4 + cation in symmetry space. It is unraveled that the Jahn-Teller deformation from C3v to C2v geometries takes a characteristic time of 20 ± 7 fs for this system. Classical and quantum molecular dynamics simulations agree well with the measurement, and reveal dynamics for the build-up of the C2v structure involving complex revival process of multiple vibrational pathways of the CH 4 + cation. The Jahn-Teller effect is the spontaneous symmetry breaking of the molecular structure caused by the coupling of electrons and nuclei. Here the authors use ultrafast Coulomb explosion imaging to map the evolution of the fundamental symmetry lowering process in photoionized methane within around 20fs. [ABSTRACT FROM AUTHOR]

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Modification of semiconductor thin films by Swift Heavy Ion (SHI) beam irradiation is a unique technique for property improvement. In the present investigation, Cadmium Zinc Telluride (CZT) thin films of thickness 100 nm are deposited on glass substrates by the thermal evaporation method. These films are irradiated with 100 MeV Ni ion beams at a fluence of 1×1012 ions/cm2 and 5×1012 ions/cm2. The SHIinduced surface modifications are studied by Atomic Force Microscopy (AFM). The structural properties are investigated using X-ray diffraction (XRD) technique. Optical characterization is carried out using UV–Vis spectroscopy. The SHI irradiation on CZT films results in grain fragmentation. Phase transformation and widening of bandgap is also observed after SHI irradiation. The SHIinduced property modifications are explained in the framework of 'coulomb explosion and thermal spike model'. [ABSTRACT FROM AUTHOR]

Flows of ions with energies on the order of megaelectronvolts, which propagate both in the axial direction and in the direction perpendicular to the symmetry axis of the discharge, are recorded in a high-current low inductance vacuum spark. Estimates based on the measurements of the total charge of suprathermal electrons emitted from the region of the waist of the current channel in the axial direction, as well as the total number of ions of the indicated energies show that the recorded ion energies correspond quite well to the value that can be achieved as a result of the Coulomb explosion of the Debye waist layer at the stage preceding the radiation compression. [ABSTRACT FROM AUTHOR]

To establish the fundamental understanding of the fragmentation dynamics of highly positive charged nano- and bio-materials, we carried out on-the-fly classical trajectory calculations on the fragmentation dynamics of C60 q+ (q ≥ 20-60). We used the UB3LYP/3-21G level of density functional theory and the self-consistent charge density-functional based tight-binding theory. For q > 20, we found that a two-step explosion mechanism governs the fragmentation dynamics: C60 q+ first ejects singly and multiply charged fast atomic cations Cz + (z ≥ 1) via Coulomb explosions on a timescale of 10 fs to stabilize the remaining core cluster. Thermal evaporations of slow atomic and molecular fragments from the core cluster subsequently occur on a timescale of 100 fs to 1 ps. Increasing the charge q makes the fragments smaller. This two-step mechanism governs the fragmentation dynamics in the most likely case that the initial kinetic energy accumulated upon ionization to C60 q + by ion impact or X-ray free electron laser is larger than 100 eV. [ABSTRACT FROM AUTHOR]

Strong electronic stopping power of swift ions in a semiconducting or insulating substrate can lead to localized electron stripping. The subsequent repulsive interactions among charged target atoms can cause Coulomb explosion. Using molecular dynamics simulation, we simulate Coulomb explosion in silicon by introducing an ionization pulse lasting for different periods, and at different substrate temperatures. We find that the longer the pulse period, the larger the melting radius. The observation can be explained by a critical energy density model assuming that melting required thermal energy density is a constant value and the total thermal energy gained from Coulomb explosion is linearly proportional to the ionization period. Our studies also show that melting radius is larger at higher substrate temperatures. The temperature effect is explained due to a longer structural relaxation above the melting temperature at original ionization boundary due to lower heat dissipation rates. Furthermore, simulations show the formation of shock waves, created due to the compression from the melting core. [ABSTRACT FROM AUTHOR]

We experimentally reconstructed the structure of the N2Ar van der Waals complex with the technique of laser-based channel-selected Coulomb explosion imaging. The internuclear distance between the N2 center of mass and the Ar atom, i.e., the length of the van der Waals bond, was determined to be 3.88 Å from the two-body explosion channels. The angle between the van der Waals bond and the N2 principal axis was determined to be 90° from the three-body explosion channels. The reconstructed structure was contrasted with our high level ab initio calculations. The agreement demonstrated the potential application of laser-based Coulomb explosion in imaging transient molecular structure, particularly for floppy van der Waals complexes, whose structures remain difficult to be determined by conventional spectroscopic methods. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the dissociative photoionization of CHBrCl2 molecules in a femtosecond laser field by time-of-flight mass spectrum and dc-slice imaging technology. The results suggest that the low kinetic energy components are from the dissociative ionization process of single-charged molecular ions. The angular distribution of fragment Cl+ ions can be attributed to the features of dissociative state and molecular configuration, and that of Br+ ions results from the electronic wave-packet evolution and combination of the multi-dissociation processes. The high kinetic energy components are from the Coulomb explosion of multi-charged molecular ions, and the error of the C-Br distance involved in the Coulomb explosion can be explained by the movement of the effective charge center of the polyatomic molecule.

Dissociation mechanisms are studied by ab initio molecular dynamics simulations based on density functional theory for the highly charged bromophenol (C6H4OHBr)n+ (n ≤ 10) in the ground electronic state and in an electronic state which has a high electronic temperature Te characterized by Fermi–Dirac distribution. In the case of the ground state, the dissociation occurs through a sequential multi-stage process. At times shorter than 20 fs after the molecule is charged, hydrogens are dissociated from the molecule and, subsequently, the carbon ring breaks at about 150 fs In the case of an electronic state with high Te, the mechanism changes from a sequential dissociation process to a simultaneous process occurring at Te > 5 eV. To estimate the charge transfer time in a molecular bromide parent ion with +6 charge, which is generated through Auger cascades, we also performed nonadiabatic quantum-mechanical molecular dynamics (NAQMD) simulations that include the effects of nonadiabatic electronic transition with a surface-hopping approach. [ABSTRACT FROM AUTHOR]

XUV multiphoton ionization of molecules is commonly used in free-electron laser experiments to study charge transfer dynamics. However, molecular dissociation and electron dynamics, such as multiple photon absorption, Auger decay, and charge transfer, often happen on competing time scales, and the contributions of individual processes can be difficult to unravel. We experimentally investigate the Coulomb explosion dynamics of methyl iodide upon core–hole ionization of the shallow inner-shell of iodine (4d) and classically simulate the fragmentation by phenomenologically introducing ionization dynamics and charge transfer. Under our experimental conditions with medium fluence and relatively long XUV pulses (∼75 fs), we find that fast Auger decay prior to charge transfer significantly contributes to the charging mechanism, leading to a yield enhancement of higher carbon charge states upon molecular dissociation. Furthermore, we argue for the existence of another charging mechanism for the weak fragmentation channels leading to triply charged carbon atoms. This study shows that classical simulations can be a useful tool to guide the quantum mechanical description of the femtosecond dynamics upon multiphoton absorption in molecular systems. [ABSTRACT FROM AUTHOR]