Ion Kinetic Energy Research Articles

Multiphoton breakdown of acetylene; formation of organic building block fragments.

Mass resolved REMPI spectra and electron and ion velocity map images were recorded for REMPI of acetylene in the case of two-photon resonant excitations to low lying 3p and 4p Rydberg states. Combined data analysis of ion signal intensities and electron and ion kinetic energy release distribution revealed multiphoton-fragmentation processes in terms of photodissociation and photoionization channels to form the molecular ion, C2H2+ and the fragment ions H+, C+, CH+, CH2+, C2+ and C2H+. The ratio of fragment ion formation over the parent ion formation increases with excitation energy. To a large extent, multiphoton-fragmentation involves the initial breakdown of the molecule into ground and excited state neutral fragments by two-, three- and four-photon dissociation processes prior to multiphoton ionization. The three-photon dissociation processes via superexcited molecular state(s) are found to be the most important and electronically excited fragment species playing a significant role in the overall multiphoton-fragmentation. Furthermore, the data are indicative of the involvement of secondary photodissociation processes and provide information on fragment energetics as well as state interactions. The question, whether acetylene could be an important source of building block fragments for the formation of organic molecules in interstellar space, is addressed.

Determination of the Plasma Delay Time in PIPS detectors for fission fragments at the LOHENGRIN spectrometer

The VElocity foR Direct particle Identification spectrometer (VERDI) is a 2E-2v fission spectrometer that allows the measurement of the total mass distribution of secondary fission fragments with a resolving power of 1-2 u. It consists of two time-of-flight (ToF) arms, with one Micro Channel Plate (MCP) detector and up to 32 Silicon PIPS (Passive Implanted Planar Silicon) detectors per arm. The MCPs provide the start timing signals and the PIPS detectors provide both the energy and the stopping ToF signals. In real conditions, the PIPS signals are affected by the formation of plasma from the interaction between the heavy ions and the detector material. The plasma contributes to a reduction in signal amplitude, resulting in a Pulse Height Defect (PHD), and introduces a signal delay, known as Plasma Delay Time (PDT). An experiment to characterize the PDT and PHD was performed at the LOHENGRIN recoil separator of the Institut Laue Langevin (ILL). Characteristic fission fragments from the 239Pu(n,f) reaction were separated based on their A/Q and E/Q ratios, allowing the measurement of a wide range of energies from 21 to 110 MeV and masses between 80 and 149 u. Six PIPS detectors were characterized to study their individual responses to the PDT and PHD effects. The signals were recorded in a digital acquisition system to completely exploit the offline analysis capabilities. Achieved combined timing and energy resolutions for fission fragments varied between 72(2) ps and 100(4) ps and 1.4% - 2% (FWHM), respectively. Preliminary PHD and PDT data are presented from the masses A=85, 95, 130 and 143. The PHD trends are strongly correlated with both the ion energy and mass. The PDT, on the other hand, shows a strong variation as a function of the ion kinetic energy but a smaller dependence on the ion mass.

Analysis and simulation of time-of-flight spectrum in Rb<sup>+</sup>-Rb hybrid trap

The time-of-flight mass spectrum of charged particles, which are created through two-step cw-laser photoionization of laser-cooled <sup>87</sup>Rb atoms in an ion-neutral hybrid trap, is quantitatively investigated to further facilitate the study of Rb<sup>+</sup>-Rb reactive collisions. A microchannel plate (MCP) is used to detect charged particles, and two spectral peaks corresponding to the <sup>87</sup>Rb<sup>+</sup> ions and the product <inline-formula><tex-math id="Z-20230423060254-1">\begin{document}$ \rm {}^{87}Rb_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.png"/></alternatives></inline-formula> of the Rb<sup>+</sup>-Rb reaction were observed in the time-of-flight spectrum, respectively. The two peaks overlapped with each other and both showed an asymmetric profile. The information about the intensity, position, and half-width of the peak for a specific ion species was derived by fitting the time-of-flight spectrum with the probability density function of the Gumbel distribution. Then the relative ion intensity was converted into absolute ion number through the following steps. The rate equation of the total number of ions, which includes the number of atoms, the calibration factor of MCP, and the effective decay rate of ions in the ion trap, was established by modeling the photoionization of atoms. Combined with the absolute number of atoms measured by absorption imaging, the calibration factor in converting the ion intensity into the ion number was derived and the relative ion intensity was converted into the absolute number of ions. This provides a method of calibrating the MCP. The reliability of our calibration method was proved by the fact that the calibration factor in converting the intensity measured by MCP into particle number is independent of the duration of photoionization, the intensity and wavelength of the ionizing laser. Moreover, in order to explain the relationship between the peak width and temperature of the corresponding ion species, the time-of-flight spectra of the ions trapped in the ion trap were simulated by using COMSOL Multiphysics. The simulation results demonstrated that the large ion kinetic energy results in a narrow spectral peak. In sum, we quantitatively analyze and simulate the time-of-flight spectrum of the photoionization of cold atoms in the Rb<sup>+</sup>-Rb hybrid trap. The absolute number of ions is obtained by the intensity of the spectral peak, and the width of the spectral peak is related to the temperature of the ions. These results lay a foundation for the in-depth analysis of the ion-atom reaction collision and charged particle temperature relaxation in the photoionization of cold atoms, and thus further elucidating the subsequent collisional dynamics of ultracold plasmas.

The origin of isomerization of aniline revealed by high kinetic energy ion mobility spectrometry (HiKE-IMS).

Although aniline is a relatively simple small molecule, the origin of its two peaks observed in ion mobility spectrometry (IMS) has remained under debate for at least 30 years. First hypothesized as a difference in protonation site (amine vs. benzene ring), each ion mobility peak differs by one Dalton when coupled with mass spectrometry where the faster mobility peak is the molecular ion peak, and the slower mobility peak is protonated. To complicate the deconvolution of structures, some previous literature shows the peaks as unresolved and thus proposes these species exist in equilibrium. In this work, we show that when measured with high kinetic energy ion mobility spectrometry (HiKE-IMS), the two peaks observed in spectra of both aniline and all n-fluoroanilines are fully separated (chromatographic resolution from 2-7, Rp > 110) and therefore not in equilibrium. The HiKE-IMS is capable of changing ionization conditions independently of drift region conditions, and our results agree with previous literature showing that ionization source settings (including possible fragmentation at this stage) are the only influence determining the speciation of the two aniline peaks. Finally, when the drift and reactant gas are changed to nitrogen, a third peak appears at high E/N for 2-fluoroaniline and 4-fluoroaniline for the first time in reported literature. As observed by HiKE-IMS-MS, the new third peak is also protonated showing that the para-protonated aniline and resulting fragment ion, molecular ion aniline, can be fully separated in the mobility domain for the first time. The appearance of the third peak is only possible due to the increased separation of the other two peaks within the HiKE-IMS.

Strategies for Improved Wettability of Polyetheretherketone (PEEK) Polymers by Non-Equilibrium Plasma Treatment

Polyetheretherketone (PEEK) is the material of choice in several applications ranging from the automotive industry to medicine, but the surface properties are usually not adequate. A standard method for tailoring surface properties is the application of gaseous plasma. The surface finish depends enormously on the processing parameters. This article presents a review of strategies adapted for improved wettability and adhesion of PEEK. The kinetics of positively charged ions, neutral reactive plasma species, and vacuum ultraviolet radiation on the surface finish are analyzed, and synergies are stressed where appropriate. The reviewed articles are critically assessed regarding the plasma and surface kinetics, and the surface mechanisms are illustrated. The directions for obtaining optimal surface finish are provided together with the scientific explanation of the limitations of various approaches. Super-hydrophilic surface finish is achievable by treatment with a large dose of vacuum ultraviolet radiation in the presence of oxidizing gas. Bombardment with positively charged ions of kinetic energy between about 100 and 1000 eV also enable high wettability, but one should be aware of excessive heating when using the ions.

Investigation of charged particles dynamics along with self-generated electric and magnetic fields in axially resolved laser-induced magnesium plasma

Laser ablated Mg plasma was generated by employing Nd-YAG laser (532 nm, 10 ns). Faraday cups with Electric and Magnetic probes have been employedto evaluate axial plasma parameters and Self-Generated Electric and Magnetic Fields (SGEMFs) at various axial distances from target (1 cm to 4 cm) and at various laser irradiances 1.8 GW/cm2 to 4.5 GW/cm2. The evaluated number densities of ions vary from 1.4 × 1013 cm−3 to 6.91 × 1013 cm−3 and electron number densities variation is from 2.38 × 1013 cm−3 to 5.15 × 1013 cm−3. The electron temperature varies from 1.3 eV to 125 eV, whereas, ion kinetic energies vary from 114 eV to 385 eV. Moreover, self-generated electric field variation is from 0.28 V/cm to 20 V/cm and magnetic field is from 978 Gauss to 2628 Gauss. Furthermore, the maxima of ion signal amplitude have been observed at 3 cm distance from target, whereas, electron signals amplitude decreases as Faraday cup to target distance increases. Both evaluated SGEMFs show decreasing trends with increasing target to probe distances and increase with increasing laser irradiance. It is observed that the shape of SGEMFs signals have been significantly affected by increasing laser irradiances and transform from unipolar to dipolar. The charge separation of plasma species, two-electron temperature distribution and bipolar signals of SGEMFs confirm the quadruple distribution of charges in plasma. It uncovers the importance of ion and electron number density gradients in plasma.

Strongly anisotropic ion emission in the expansion of Nd:YAG-laser-produced plasma

We present results from a combined experimental and numerical simulation study of the anisotropy of the expansion of a laser-produced plasma into vacuum. Plasma is generated by nanosecond Nd:YAG laser pulse impact (laser wavelength λ=1.064 μm) onto tin microdroplets. Simultaneous measurements of ion kinetic energy distributions at seven angles with respect to the direction of the laser beam reveal strong anisotropic emission characteristics, in close agreement with the predictions of two-dimensional radiation-hydrodynamic simulations. Angle-resolved ion spectral measurements are further shown to provide an accurate prediction of the plasma propulsion of the laser-impacted droplet.

Perpendicular Subcritical Shock Structure in a Collisional Plasma Experiment.

We present a study of perpendicular subcritical shocks in a collisional laboratory plasma. Shocks are produced by placing obstacles into the supermagnetosonic outflow from an inverse wire array z pinch. We demonstrate the existence of subcritical shocks in this regime and find that secondary shocks form in the downstream. Detailed measurements of the subcritical shock structure confirm the absence of a hydrodynamic jump. We calculate the classical (Spitzer) resistive diffusion length and show that it is approximately equal to the shock width. We measure little heating across the shock (<10% of the ion kinetic energy) which is consistent with an absence of viscous dissipation.

Development of a Clinical Neutron Source for Boron Neutron Capture Therapy

<h3>Purpose/Objective(s)</h3> In boron neutron capture therapy (BNCT), a source of epithermal (1 eV to 30 keV) neutrons activates high concentrations of ¹⁰B, selectively accumulated in tumor cells from infusion of a non-radioactive pharmaceutical, whose high LET reaction products fully deposit their energy within 10 microns of the reaction site. Historically, only nuclear reactors provided sufficient neutron intensity and beam quality for clinically acceptable BNCT treatments, but hospital-based BNCT is now feasible using compact accelerator sources. The present work has designed a system to produce an epithermal neutron beam using a tandem electrostatic accelerator, proton beam line, neutron-producing targets, neutron beam shaping assembly (BSA) and collimators. Testing was required to verify that this design can produce a clinically viable neutron source for BNCT in terms of total neutron yield, output reproducibility and operational stability. <h3>Materials/Methods</h3> The present neutron source uses neutrons from the ⁷Li(p,n)⁷Be reaction at nominal proton energy and current of 2.5 MeV and 10 mA. A negative hydrogen ion source is pre-accelerated to 200 keV and injected into the tandem accelerator, which increases the negative ion kinetic energy to half the goal proton energy at its center. A charge exchange target strips the electrons to create positively-charged protons that are further accelerated to the full operational energy at the tandem exit. The proton beam is focused and may be directed to up to three treatment rooms, each with a copper-backed target of natural lithium metal under vacuum. The maximum neutron energy from 2.5 MeV protons slowing down in lithium is 800 keV and requires moderation to the desired epithermal range. A static beam BSA surrounds the target and provides efficient neutron moderation and reflection using carefully chosen materials. The BSA's 25 cm circular exit port may be collimated to small circular epithermal beam diameters as small as 5-8 cm. <h3>Results</h3> A tandem accelerator, proton beam line and lithium target have been installed and began initial testing. Proton energy and current up to 2.3 MeV and 7 mA have been achieved for continuous operating periods exceeding 30 minutes with no energy or current degradation. Raster patterns have been designed to scan the 1-cm diameter proton beam over a 10-cm circular area on the lithium target, and water cooling of the copper backing has maintained maximum target temperatures below 150°C. The measured lithium deposition uniformity is expected to translate to a neutron yield uniformity better than 5%. <h3>Conclusion</h3> This BNCT neutron source has demonstrated operational stability and reproducibility of proton energy, proton current and neutron production. These measurements support an expectation that the equipment currently undergoing evaluation, in combination with the planned BSA, will meet the necessary requirements for a hospital-based, clinical BNCT system.

Experimental study of dynamics and soft X-ray emission of laser produced plasma from low-density foam Ti targets

Low-density foam targets are expected to be good candidates for efficient laser produced plasma (LPP) and soft X-ray (SXR) sources due to the less energetic debris compared with solid targets. Three Ti targets with different densities were irradiated by a pulsed Nd:YAG laser in vacuum. The average ion energy and the time-of-flight (TOF) peak voltage decreased as the Ti target density decreased. Furthermore, the differences among the three Ti targets increased with increasing laser intensity. The average ion energy of low-density foam Ti targets had a slightly weaker angular dependence compared with solid Ti targets. The plasma plume optical images illustrated that solid Ti plasma expanded faster in the direction of laser incidence with stronger anisotropy compared to foam Ti plasma. In addition, the optical radiation intensity integrated from a wavelength region of 200–850 nm of plasma plume increased with decreasing initial target density, which indicated that more absorbed laser energy was converted to plasma optical radiation energy (internal energy) instead of ion kinetic energy for targets with lower initial densities. The SXR radiation had no significant difference among the three Ti targets. These results demonstrate that appropriately reducing the initial target density can significantly reduce kinetic energy of ion debris without affecting the SXR radiation output.

Nanostructures evolution assessment and spectroscopic properties modification induced by electronic energy loss in KTaO3 crystal

Modifications of micro/nanostructure and photoelectric properties under swift ion irradiation (645 MeV Xe35+) of KTaO3 crystal with varying electronic energy losses (7.2–31.4 keV/nm) and ion velocities (0.18–5.00 MeV/u) have been studied by combining experimental and calculated approaches. The i-TS calculations combined with molecular dynamics simulations are compared with the experimental observations, revealing the inner track fine structures from individual spherical defects to continuous ion tracks with core–shell morphologies, and a quantitative relationship, including the melting (0.42 eV/atom), damage (0.75 eV/atom), and amorphous (1.71 eV/atom) thresholds, is established to successfully predict the inner disorder/amorphous proportions and track damage morphologies. The surface nanostructures of nanohillocks (isolated or partial overlaps) and nanopits (serious overlaps) directly depend on the combined action of the deposited potential and kinetic energies of incident ions, which induce local melting and sublimation in the near-surface region. Owing to the decreased recombination and the increased separation efficiency between electrons and holes, the higher photogenerated charge carrier mobility enhanced the photocurrent effect, further optimizing the photoconductivity performance in Xe35+-irradiated KTaO3. Therefore, controlled defect engineering using the ion irradiation technique, as an effective strategy, could design tailored nanostructure systems and regulate photoelectric properties, further promoting the development of novel technological applications.

Molecular Dynamics Simulations of Ion Extraction from Nanodroplets for Ionic Liquid Electrospray Thrusters

AbstractMolecular dynamics (MD) simulations were performed for ion extraction from electrospray thrusters to investigate relevant extraction processes numerically. To approximate the electrospray jet tip, a simulation domain consisting of 4-5 nm-sized ionic liquid droplets was used. The extracted ion angles and kinetic energies from EMI–BF4 (1-ethyl-3-methylimidazolium tetrafluoroborate) and EMI–Im (1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide) droplets were quantified by applying uniform electric fields of 1.3–1.7 V nm−1. The MD simulations are in great agreement with simulations presented in the literature and consistently show a greater preference for monomer emission than reported experimentally. At field strengths above 1.5 V nm−1, apparent droplet fracturing and breakup lead to an increase in ion angular velocity distributions. Greater mobility of EMI–BF4 ions than EMI–Im was also observed, indicative of the crucial role of cation-anion hydrogen bond strengths in ion extraction and beam composition between different propellants.

Investigations on the CuI thin films production by pulsed laser deposition

CuI thin films were deposited by pulsed laser deposition (PLD) in various Ar atmospheres. Control over the morphology, structure and defect nature of the deposited films was attempted by in-situ plasma diagnostics. The deposited films presented stoichiometric crystallinity on the full range of experimental condition with no residual oxidation, as per XRD and XPS measurements. Band gap tailoring was achieved by controlling the plasma ion kinetic energy with optimum conditions being defined by Cu and I ionic groups with kinetic energies surpassing 200 eV. Variation in Ar pressure allowed control over the nature of vacancies from VI + Cui to predominantly VCu. In situ plasma measurements revealed that the addition of Ar leads to the preferentially scattering of the Cu ions in the plasma which subsequently leads Cu ions energy losses. This energetic imbalance in the plasma is reflected in the disappearance of interstitial Cui vacancies and the increase in VCu. The generation of Cui vacancies was achieved in high temperature plasma and low plasma potential (Te > 20 eV and Vp < 8 V) conditions. The increase in plasma potential balances the accelerations during expansion and maintaining a high average temperature at the substrate inducing crystallinity even above 5 Pa or Ar.

Effects of amplitude modulated capacitively coupled discharge Ar plasma on kinetic energy and angular distribution function of ions impinging on electrodes: particle-in-cell/Monte Carlo collision model simulation

We investigated the effects of amplitude modulated (AM) capacitively coupled Ar discharge plasma on the ion energy distribution function (IEDF) and the ion angular distribution function (IADF) incident on electrodes using the particle-in-cell/Monte Carlo collision model. For AM discharge, the electron density and electron temperature and the kinetic energy and angle of ions incident on the ground electrode change periodically with AM frequency, whereas ones for continuous wave discharge are almost constant. For AM discharge, the plasma had hysteresis characteristics. The peak energy of IEDF varies from 53 to 135 eV and the FWHM of IADF varies from 1.82 to 3.34 degrees for gas pressure 10mTorr, the peak-to-peak input voltage 400 V and AM level of 50%. The variation width of the peak energy of IEDF and FWHM of IADF increases with the AM level. These effects of AM method discharge are more noticeable at lower pressures. Thus, the AM discharge offers a way to control simultaneously IEDF and IADF, which opens a new avenue for plasma processes such as an ALD-like PECVD.

Suppression of reconnection in polarized, thin magnetotail current sheets: 2D simulations and implications

Many in situ spacecraft observations have demonstrated that magnetic reconnection in the Earth's magnetotail is largely controlled by the pre-reconnection current sheet configuration. One of the most important thin current sheet characteristics is the preponderance of electron currents driven by strong polarized electric fields, which are commonly observed in the Earth's magnetotail well before the reconnection. We use particle-in-cell simulations to investigate magnetic reconnection in the 2D magnetotail current sheet with a finite magnetic field component normal to the current sheet and with the current sheet polarization. Under the same external driving conditions, reconnection in a polarized current sheet is shown to occur at a lower rate than in a nonpolarized current sheet. The reconnection rate in a polarized current sheet decreases linearly as the electron current's contribution to the cross-tail current increases. In simulations with lower background temperature, the reconnection electric field is higher. We demonstrate that after reconnection in such a polarized current sheet, the outflow energy flux is mostly in the form of ion enthalpy flux, followed by electron enthalpy flux, Poynting flux, ion kinetic energy flux, and electron kinetic energy flux. These findings are consistent with spacecraft observations. Because current sheet polarization is not uniform along the magnetotail, our results suggest that it may slow down reconnection in the most polarized near-Earth magnetotail and thereby move the location of reconnection onset downtail.

Dissociation of State-Selected Ions Studied by Fixed-Photon-Energy Double-Imaging Photoelectron Photoion Coincidence: Cases of O2+ and CH3F+

This study presents the method of fixed-photon-energy double-imaging photoelectron photoion coincidence (i2PEPICO) utilized to investigate the dissociation of state-selected ions. Vacuum ultraviolet (VUV) synchrotron radiation at one fixed photon energy of hν = 21.2 eV, the He(I) atomic resonance energy, is employed as a light source to ionize molecules. Various dynamic information including time-of-flight (TOF) mass spectra, mass-selected photoelectron spectra (PES), and electron and ion kinetic energy correlation diagrams corresponding to each mass are obtained efficiently with the multiplexed capabilities of i2PEPICO, thereby revealing the detailed dissociation mechanisms of ions. As representative examples, dissociation of state-selected O2+ ions prepared in the b4∑g− and B2∑g− electronic states and CH3F+ ions in the X2E, A2A1, and B2E states were selected and investigated.

Statistical Study of Favorable Foreshock Ion Properties for the Formation of Hot Flow Anomalies and Foreshock Bubbles

AbstractHot flow anomalies (HFAs) and foreshock bubbles (FBs) are frequently observed in Earth's foreshock, which can significantly disturb the bow shock and therefore the magnetosphere‐ionosphere system and can accelerate particles. Previous statistical studies have identified the solar wind conditions (high solar wind speed and high Mach number, etc.) that favor their generation. However, backstreaming foreshock ions are expected to most directly control how HFAs and FBs form, whereas the solar wind may partake in the formation process indirectly by determining foreshock ion properties. Using Magnetospheric Multiscale mission and Time History of Events and Macroscale Interactions during Substorms mission, we perform a statistical study of foreshock ion properties around 275 HFAs and FBs. We show that foreshock ions with a high foreshock‐to‐solar wind density ratio (&gt;∼3%), high kinetic energy (&gt;∼600 eV), large ratio of kinetic energy to thermal energy (&gt;∼0.1), and large ratio of perpendicular temperature to parallel temperature (&gt;∼1.4) favor HFA and FB formation. We also examine how these properties are related to solar wind conditions: high solar wind speed and oblique bow shock (angle between the interplanetary magnetic field and the bow shock normal ) favor high kinetic energy of foreshock ions; foreshock ions have large ratio of kinetic energy to thermal energy at large (&gt;30°); small (&lt;30°), high Mach number, and closeness to the bow shock favor a high foreshock‐to‐solar wind density ratio. Our results provide further understanding of HFA and FB formation.

The impact of ion mobility coefficients on plasma discharge characteristics

In this paper, the high-accuracy ion mobility coefficient based on the Chapman–Enskog approximation to the solution of the Boltzmann equation for low pressure radio frequency plasma discharges is presented. We employ two-dimensional fluid simulations of the argon filled axisymmetric reactor, where the effect of new ion-kinetics-based fluid closure is compared to theoretical expressions and experimental data. The spatial profiles of plasma composition in the low pressure radio frequency capacitively coupled plasma are presented, which includes the metastable reactions in the simulation. Moreover, inelastic collision integrals terms, due to charge exchange inelastic collisions between ions and neutral species, have been also considered. A Monte Carlo simulation of kinetic ion energy distribution of impinging on the radio frequency powered electrode provides a measure of accuracy of the new transport model. From our simulation, the results that mirror the influence of ion mobility coefficient obtained by the Chapman–Enskog method on plasma physical quantities under different pressures, frequencies, and electrode gaps is in good agreement with experimental measurement results and theoretical expressions.

Determination of the critical temperature of Nb–Al alloys from the plasma parameters of a vacuum arc cathode spot

The plasma of pulsed-periodic splashes of explosive electron emission forms a vacuum arc cathode spot. The average parameters of the plasma can be evaluated from the parameters of the critical state of a metal for different materials. According to the measurements (Zöhrer et al 2020 Plasma Sources Sci. Technol. 29 025022) of the average charge and the kinetic energy of plasma ions, the critical temperature and cohesive energy for Nb–Al alloys was evaluated within our model. It was close to the value corresponding to pure aluminum for all component ratios Nb/Al = ¼, ⅔, ¾. We have described the experimentally measured values of the cathode potential fall using the obtained magnitudes of critical temperature in the empirical ‘cohesive energy rule’ and have reproduced the observed deviation from linearity in form of U or V shaped dependencies. The obtained results make possible to evaluate the critical temperature and cohesive energy from the parameters of the vacuum arc plasma.

Influence of Sample Gas Humidity on Product Ion Formation in High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS).

High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) chemically ionize gaseous samples via reactant ions and separate the generated ions by their motion in a neutral gas under the influence of an electric field. Operation at reduced pressures of 10-40 mbar allows for reaching high reduced electric field strengths (E/N) of up to 120 Td. At these high E/N, the generated ions gain the namesake high kinetic energies, leading to a decrease in cluster size of the reactant ions by increasing the reaction rate of collision-induced cluster dissociation of hydrates. In positive ion polarity and in purified air, H3O+(H2O)n, NO+(H2O)n, and O2+•(H2O)p are the most abundant reactant ions. In this work, we investigate the effect of varying sample gas humidity on product ion formation for several model substances. Results show that increasing the sample gas humidity at high E/N of 120 Td shifts product ion formation from a charge transfer dominated reaction system to a proton transfer dominated reaction system. For HiKE-IMS operated at high E/N, the reduction in cluster size of reactant ions allows ionization of analytes with low proton affinity even at high relative humidity in the sample gas of RH = 75% at 303.15 K and 1013.25 hPa. In contrast to conventional IMS, where increasing the sample gas humidity inhibits ionization for various analytes, increasing sample gas humidity in HiKE-IMS operated at 120 Td is actually beneficial for ionization yield of most analytes investigated in this work as it increases the number of H3O+(H2O)n.