Search Results (25)

Boehmite has been widely used in theoretical research and industry, especially for hazardous material processing. For the liquid-phase treating process, the interfacial properties of boehmite are believed to be affected by pH conditions, which change its physicochemical behavior. However, molecular-level detection on cluster ions is challenging when using bulk approaches. Herein we employ in situ vacuum ultraviolet single-photon ionization mass spectrometry (VUV SPI-MS) coupled with a vacuum-compatible microreactor system for analysis at the liquid–vacuum interface (SALVI) to investigate the solute molecular composition of boehmite under different pH conditions for the first time. The mass spectral results show that more complex clustering of solute molecules exists at the solid–liquid (s–l) interface than conventionally perceived in a “simple” aqueous solution. Besides solute ions, such as boehmite molecules and fragments, the composition and appearance energies of these newly discovered solvated cluster ions are determined by VUV SPI-MS in different pH solutions. We offer new results for the pH-dependent effect of boehmite and provide insights into a more detailed solvation mechanism at the s–l interface. By comparing the key products under different pH conditions, fundamental understanding of boehmite dissolution is revealed to assist the engineering design of waste processing and storage solutions. Full article

The valence-shell electronic state spectroscopy of β-butyrolactone (CH₃CHCH₂CO₂) is comprehensively investigated by employing experimental and theoretical methods. We report a novel vacuum ultraviolet (VUV) absorption spectrum in the photon wavelength range from 115 to 320 nm (3.9–10.8 eV), together with ab initio quantum chemical calculations at the time-dependent density functional (TD-DFT) level of theory. The dominant electronic excitations are assigned to mixed valence-Rydberg and Rydberg transitions. The fine structure in the CH₃CHCH₂CO₂ photoabsorption spectrum has been assigned to C=O stretching, $v_7^{\prime }\left(a\right)$, CH₂ wagging, $v_{14}^{\prime }\left(a\right)$, C–O stretching, $v_{22}^{\prime }\left(a\right)$, and C=O bending, $v_{26}^{\prime }\left(a\right)$ modes. Photolysis lifetimes in the Earth’s atmosphere from 0 km up to 50 km altitude have been estimated, showing to be a non-relevant sink mechanism compared to reactions with the ^•OH radical. The nuclear dynamics along the C=O and C–C–C coordinates have been investigated at the TD-DFT level of theory, where, upon electronic excitation, the potential energy curves show important carbonyl bond breaking and ring opening, respectively. Within such an intricate molecular landscape, the higher-lying excited electronic states may keep their original Rydberg character or may undergo Rydberg-to-valence conversion, with vibronic coupling as an important mechanism contributing to the spectrum. Full article

The development of efficient scintillators emitting in the red and/or infrared spectral range represents an important scientific challenge, as such materials could find numerous practical applications. This work studies newly grown CsI:Yb,Sm and CsI:Eu,Sm single crystals demonstrating red and infrared luminescence. We measured luminescence spectra in the visible and near-IR range, excitation spectra across visible, UV, VUV, and X-ray ranges, Raman spectra, and thermoluminescence spectra. The results show that divalent europium and ytterbium ions can efficiently transfer excitation to samarium ions. The light output of the obtained crystals under X-ray excitation was roughly estimated from the X-ray luminescence spectra, with expected values of 37,000 photons/MeV for CsI:Yb,Sm and 40,000 photons/MeV for CsI:Eu,Sm. Full article

A single crystal of YAl₃(BO₃)₄ was grown using the top-seeded solution growth method. The vacuum ultraviolet (VUV) excitation spectrum, monitored at the emission wavelength of 312 and 372 nm, showed a narrow excitation band at around 162 nm, which is located near the absorption edge of the YAl₃(BO₃)₄ host. Upon VUV excitation at 162 nm, the characteristic self-trapped exciton (STE) emission bands were observed at 312 and 372 nm. The X-ray excited scintillation spectrum shows a broad emission band peaking at 310 nm with a weak shoulder band at around 375 nm, which is consistent with photoluminescence, and can thus be assigned to the STE emission. The scintillation light yield under irradiation at a ²⁵²Cf-thermal neutron reached 2700 photons/thermal neutron. Full article

In this work, we provide results from a joint experimental and theoretical study of the vibronic features of cyclohexane (C₆H₁₂) in the photon energy range of 6.8–10.8 eV (182–115 nm). The high-resolution vacuum ultraviolet (VUV) photoabsorption measurements, together with quantum chemical calculations at the time-dependent density functional theory (TDDFT) level, have helped to assign the major electronic excitations to mixed valence–Rydberg and Rydberg transitions. The C₆H₁₂ photoabsorption spectrum shows fine structure which has been assigned to CH₂ scissoring, $v_3^{\prime }\left(a_{1g}\right)$, CH₂ rocking, $v_4^{\prime }\left(a_{1g}\right)$, C–C stretching, $v_5^{\prime }\left(a_{1g}\right)$, and CCC bending/CC torsion, $v_{24}^{\prime }\left(e_g\right),$ modes. Molecular structure calculations at the DFT level for the neutral and cationic electronic ground-states have shown the relevant structural changes that are operative in the higher-lying electronic states. Photolysis lifetimes in the Earth’s atmosphere are shown to be irrelevant, while the main atmospheric sink mechanism is the reaction with the ^•OH radical. Potential energy curves have been obtained at the TDDFT level of theory, showing the relevance of interchange character mainly involving the CH₂ scissoring, $v_3^{\prime }\left(a_{1g}\right),$ and CH₂ rocking, $v_4^{\prime }\left(a_{1g}\right),$ modes, while Jahn–Teller distortion yields weak vibronic coupling involving the non-totally symmetric CCC bending/CC torsion, $v_{24}^{\prime }\left(e_g\right),$ mode. Full article

We report absolute high-resolution vacuum ultraviolet (VUV) photoabsorption cross-sections of carbon tetrachloride (CCl₄) in the photon energy range 5.0–10.8 eV (248–115 nm). The molecular spectrum and electronic structure have been comprehensively investigated together with quantum chemical calculations, providing geometries, bond lengths, vertical excitation energies and oscillator strengths. The major electronic excitations have been assigned to valence and Rydberg transitions which are also accompanied by vibrational excitation assigned to degenerate stretching, $v_3^{\prime }\left(t_2\right)$ and degenerate deformation $v_4^{\prime }\left(t_2\right)$ modes. The rather complex nuclear dynamics along the degenerate deformation mode, $v_4^{\prime }\left(t_2\right)$, have been thoroughly investigated by Time-Dependent Density Functional Theory (TD-DFT) method. The relevant Jahn–Teller distortion operative within the lowest-lying electronic excited-state is shown here for the first time in order to yield a weak absorption feature at 6.156 eV. Further calculations on the potential energy curves for the singlet excited-states along the C–Cl stretching coordinate show the relevance of efficient C–Cl bond excision. Full article

In this paper, a new light event acquisition chain in a three-gamma liquid xenon prototype for medical nuclear imaging is presented. The prototype implements the Multi-Time-Over-Threshold (MTOT) method. This method surpasses the Single-Time-Over-Threshold (STOT) by precisely determining both the number of vacuum ultraviolet (VUV) photons detected by each photomultiplier tube (PMT) and their arrival times for light signal measurement. Based on both the experimental and simulated results, the MTOT method achieved a 70% improvement in reconstructing photoelectrons (PEs) and enhanced the precision of the arrival time estimation by 20–30% compared with STOT. These results will enable an upgrade of the XEMIS2 (Xenon Medical Imaging System) camera, improving its performance as the imaged activity increases. Full article

Fluorides have a wide bandgap and therefore, when doped with the appropriate ions, exhibit emissions in the ultraviolet C (UVC) region. Some of them can emit two photons in the visible region for one excitation photon, having a quantum efficiency greater than 100%. In a novel exploration, praseodymium (Pr³⁺) ions were introduced into KLaF₄ crystals for the first time. The samples were obtained according to a high-temperature solid-state reaction. They exhibited an orthorhombic crystal structure, which has not been observed for this lattice yet. The optical properties of the material were investigated in the ultraviolet (UV) and visible ranges. The spectroscopic results were used to analyze the Pr³⁺ electronic-level structure, including the 4f5d configuration. It has been found that KLaF₄:Pr³⁺ crystals exhibit intense luminescence in the UVC range, corresponding to multiple 4f → 4f transitions. Additionally, under vacuum ultraviolet (VUV) excitation, distinct transitions, specifically ¹S₀ → ¹I₆ and ³P₀ → ³H₄, were observed, which signifies the occurrence of photon cascade emission (PCE). The thermal behavior of the luminescence and the thermometric performance of the material were also analyzed. This study not only sheds light on the optical behavior of Pr³⁺ ions within a KLaF₄ lattice but also highlights its potential for efficient photon management and quantum-based technologies. Full article

Thin-layer Al/MgF₂ coatings are currently used for extraterrestrial far-UV astronomy as the primary and secondary mirrors of telescopes (such as “Spektr-UF”). Successful Hubble far-UV measurements have been performed thanks to MgF₂ on Al mirror coatings. Damage of such thin-layer coatings has been previously studied under exposure to high-energy electrons/protons fluxes and in low Earth orbit environments. Meanwhile, there is an interest to test the stability of such mirrors under the impact of extreme radiation fluxes from pulsed plasma thrusters as a simulation of emergency onboard situations and other applications. In the present studies, the high current and compressed plasma jets were generated by a laboratory plasma thruster prototype and operated as effective emitters of high brightness (with an integral overall wavelength radiation flux of >1 MW/cm²) and broadband radiation. The spectrum rearrangement and hard-photon cut-off at energy above E_c were implemented by selection of a background gas in the discharge chamber. The discharges in air (E_c ≈ 6 eV), argon (E_c ≈ 15 eV) and neon (E_c ≈ 21 eV) were studied. X-ray diffraction and reflectometry, electron and atomic force microscopy, and IR and visible spectroscopy were used for coating characterization and estimation of degradation degree. In the case of the discharges in air with photon energies of E < 6 eV, only individual nanocracks were found and property changes were negligible. In the case of inert gases, the energy fraction was ≈50% in the VUV range. As found for inert background gases, an emission of such hard photons with energies higher than the MgF₂ band gap energy of ≈10.8 eV caused a drastic light-induced ablation and degradation of the irradiated coatings. The upward trend of degradation with an increasing of the maximum photon energies was detected. The obtained data on the surface destruction are useful for the design of methods for coating stability tests and an understanding of the consequences of emergencies onboard space research stations. Full article

Single photon ionization (SPI) based on vacuum ultraviolet (VUV) lamps has been extensively investigated and applied due to its clean mass spectra as a soft ionization method. However, the photon energy of 10.6 eV and photon flux of 10¹¹ photons s⁻¹ of a commercial VUV lamp limits its range of ionizable analytes as well as its sensitivity. This work designs a chemical ionization focusing integrated (CIFI) ionization source time-of-flight mass spectrometry (TOFMS) based on a VUV lamp for the detection of volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs). The photoelectrons obtained from the VUV lamp via the photoelectric effect ionized the oxygen and water in the air to obtain the reagent ions. The ion–molecule-reaction region (IMR) is constituted by a segmented quadrupole that radially focuses the ions using a radio-frequency electric field. This significantly enhances the yield and transport efficiency of the product ions leading to a great improvement in sensitivity. As a result, a 44-fold and 1154-fold increase in the signal response for benzene and pentanal were achieved, respectively. To verify the reliability of the ionization source, the linear correspondence and repeatability of benzene and pentanal were investigated. Satisfactory dynamic linearity was obtained in the mixing ratio range of 5–50 ppbv, and the relative standard deviation (RSD) of inter-day reached 3.91% and 6.26%, respectively. Finally, the CIFI−TOFMS was applied to the determination of OVOCs, and the LOD of 12 types of OVOCs reached the pptv level, indicating that the ionization source has the potential for accurate and sensitive online monitoring of atmospheric OVOCs. Full article

In this work, we investigate the relaxation processes of 2-thiouracil after UV photoexcitation to the S₂ state through the use of ultrafast, single-colour, pump-probe UV/UV spectroscopy. We place focus on investigating the appearance and subsequent decay signals of ionized fragments. We complement this with VUV-induced dissociative photoionisation studies collected at a synchrotron, allowing us to better understand and assign the ionisation channels involved in the appearance of the fragments. We find that all fragments appear when single photons with energy > 11 eV are used in the VUV experiments and hence appear through 3+ photon-order processes when 266 nm light is used. We also observe three major decays for the fragment ions: a sub-autocorrelation decay (i.e., sub-370 fs), a secondary ultrafast decay on the order of 300–400 fs, and a long decay on the order of 220 to 400 ps (all fragment dependent). These decays agree well with the previously established S₂ → S₁ → Triplet → Ground decay process. Results from the VUV study also suggest that some of the fragments may be created by dynamics occurring in the excited cationic state. Full article

Obtaining new data on the gas-dynamic responses from the polymer samples (polytetrafluoroethylene, PTFE) irradiated by powerful VUV radiation from compressed plasma flows is in the focus of the present study. An erosion type magnetoplasma compressor (MPC), a type of plasma focus discharge, was used as a radiation source. The operating voltages of the MPC were between 15 and 25 kV, the maximum measured discharge current was 200 kA, and the radiation energy in the VUV range was ≈1–2 kJ. The VUV fluxes on the sample surface were high and equal to ≈10²²–10²⁴ photons cm⁻²·s⁻¹. Double-exposure laser holographic interferometry and schlieren photography were used to diagnose and visualize the gas-dynamic structures. The spatial distribution of the parameters (temperature, pressure and concentrations of electrons and ions) was defined based on the assumption of local thermodynamic equilibrium. It has been demonstrated that the maximum temperature ranged from ≈ 10 to 15 kK in the plasma layer. The electron concentration was ≈ (0.7–1.6) × 10¹⁸ cm⁻³ in this region. The used techniques of optical diagnostics and procedures of result processing make it possible to obtain data on the dynamics of polymer ablation, which occurs when their surface is exposed to powerful energy fluxes (thermal, shock-wave, radiation, and other extreme loads). Full article

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. Full article

Oxygen plasma is widely used for enhancing the wettability of numerous polymers, including polyethylene terephthalate (PET). The treatment with plasma containing oxygen will cause surface functionalization with polar functional groups, which will, in turn, improve the wettability. However, the exact mechanisms leading to the hydrophilic or even super-hydrophilic surface finish are still insufficiently explored. The wettability obtained by plasma treatment is not permanent, since the hydrophobic recovery is usually reported. The mechanisms of hydrophobic recovery are reviewed and explained. Methods for suppressing this effect are disclosed and explained. The recommended treatment which assures stable hydrophilicity of PET samples is the treatment with energetic ions and/or vacuum ultraviolet radiation (VUV). The influence of various plasma species on the formation of the highly hydrophilic surface finish and stability of adequate wettability of PET materials is discussed. Full article

Heat-assisted plasma (HAP) treatment using He gas is known to improve the adhesive-bonding and adhesive-free adhesion properties of polytetrafluoroethylene (PTFE). In this study, we investigated the effects of He and Ar gaseous species on the HAP-treated PTFE surface. Epoxy (EP) adhesive-coated stainless steel (SUS304) and isobutylene–isoprene rubber (IIR) were used as adherents for the evaluation of the adhesive-bonding and adhesive-free adhesion properties of PTFE. In the case of adhesive bonding, the PTFE/EP-adhesive/SUS304 adhesion strength of the Ar-HAP-treated PTFE was the same as that of the He-HAP-treated PTFE. In the case of adhesive-free adhesion, the PTFE/IIR adhesion strength of the Ar-HAP-treated PTFE was seven times lower than that of the He-HAP-treated PTFE. The relation among gaseous species used in HAP treatment, adhesion properties, peroxy radical density ratio, surface chemical composition, surface modification depth, surface morphology, surface hardness, and the effect of irradiation with vacuum ultraviolet (VUV) and UV photons were investigated. The different adhesive-free adhesion properties obtained by the two treatments resulted from the changes in surface chemical composition, especially the ratios of oxygen-containing functional groups and C–C crosslinks. Full article