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The ultrafast electronic dynamics of pyrazine (C4N2H4) were studied by time-resolved photoelectron imaging (TRPEI) using the third (3ω, 4.7 eV) and fifth harmonics (5ω, 7.8 eV) of a femtosecond Ti:sapphire laser (ω). Although the photoionization signals due to the 5ω - 3ω and 3ω - 5ω pulse sequences overlapped near the time origin, we have successfully extracted their individual TRPEI signals using least squares fitting of the observed electron kinetic energy distributions. When the 5ω pulses preceded the 3ω pulses, the 5ω pulses predominantly excited the S4 (ππ*, ¹B1u+¹B2u) state. The photoionization signal from the S4 state generated by the time-delayed 3ω pulses was dominated by the D3(²B2g) ω S4 photoionization process and exhibited a broad electron kinetic energy distribution, which rapidly downshifted in energy within 100 fs. Also observed were the photoionization signals for the 3s, 3pz, and 3py members of the Rydberg series converging to D0(²Ag). The Rydberg signals appeared immediately within our instrumental time resolution of 27 fs, indicating that these states are directly photoexcited from the ground state or populated from S4 within 27 fs. The 3s, 3pz, and 3py states exhibited single exponential decay with lifetimes of 94 ± 2, 89 ± 2, and 58 ± 1 fs, respectively. With the reverse pulse sequence of 3ω - 5ω, the ultrafast internal conversion (IC) from S2(ππ*) to S1(nπ*) was observed. The decay associated spectrum of S2 exhibited multiple bands ascribed to D0, D1, and D3, in agreement with the 3ω-pump and 6ω-probe experiment described in our preceding paper [T. Horio et al., J. Chem. Phys. 145, 044306 (2016)]. The electron kinetic energy and angular distributions from S1 populated by IC from S2 are also discussed. [ABSTRACT FROM AUTHOR]

Here we compare the global‐scale morphology of Earth's the Far‐Ultraviolet (FUV) emissions observed by NASA's Global‐scale Observations of Limb and Disk (GOLD) mission to those modeled using the Global Airglow (GLOW) code with atmospheric parameters provided by Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM). The O 5S oxygen (135.6 nm) and N2 Lyman‐Birge‐Hopfield (LBH) emissions are observed over the Western hemisphere every 30 min by the GOLD instrument. The FUV brightness of the thermosphere‐ionosphere is expected to vary in systemic ways with respect to geophysical parameters, solar energy input from above, and terrestrial weather input from below. In this paper we examine the O 5S oxygen emission and the N2 LBH emission brightnesses with local time, latitude, season, tides, geomagnetic activity, and solar activity based on GOLD observations and GLOW modeling. Early GOLD observations indicate that the model effectively reproduces the brightness variations with local time and latitude but is biased low in magnitude. However, the TIEGCM is unable to accurately represent the extraordinary nighttime equatorial ionization anomaly observed by GOLD. It is also expected from these results that the signal from geomagnetic storms may obscure tidal signals. Plain Language Summary: In January 2018, a FUV instrument, the Global‐scale Observations of Limb and Disk (GOLD), was launched as a NASA mission of opportunity aboard a geostationary satellite and scientific operations began in October of 2018. GOLD views the entire disk of the Earth every 30 min, allowing the separation of geophysical variability in both space and time. This allows an unprecedented test of global models. Here, we model the Earth's upper atmosphere using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM), which produces temperature and the densities of the major chemical components of the neutral atmosphere, ionized plasma densities, and neutral air temperatures. These atmospheric temperatures and densities are used to calculate the Earth's upper atmosphere emissions in the Far‐Ultraviolet (FUV) with the Global Airglow (GLOW) model. The calculated emission rates are then used to compute the expected FUV signals as observed from geostationary orbit. In this paper, we show how the FUV brightness varies with local time, season, atmospheric activity, and solar activity. Of particular interest is that the GLOW model excels at producing FUV brightnesses that match the local time and latitude trends of the daytime observations; however, the model fails to adequately portray the extraordinary nighttime phenomena observed by GOLD. Key Points: The Global‐scale Observations of Limb and Disk (GOLD) instrument observes the Earth in the Far‐Ultraviolet (FUV) from a geostationary orbitGLOW adequately calculates the FUV brightness for various local times, latitudes, solar forcing, and lower atmospheric forcingGLOW calculations indicate the oxygen brightness varies by ±45 R and the effective temperature varies by more than 80 K due to tides [ABSTRACT FROM AUTHOR]

Second-order-derivative plus fourth-order-derivative gravity is the ultraviolet completion of second-order-derivative quantum Einstein gravity. While it achieves renormalizability through states of negative Dirac norm, the unitarity violation that this would entail can be postponed to Planck energies. As we show in this paper, the theory has a different problem, one that occurs at all energy scales, namely that the Dirac norm of the vacuum of the theory is not finite. To establish this, we present a procedure for determining the norm of the vacuum in any quantum field theory. With the Dirac norm of the vacuum of the second-order-derivative plus fourth-order-derivative theory not being finite, the Feynman rules that are used to establish renormalizability are not valid, as is the assumption that the theory can be used as an effective theory at energies well below the Planck scale. This lack of finiteness is also manifested in the fact that the Lorentzian path integral for the theory is divergent. Because the vacuum Dirac norm is not finite, the Hamiltonian of the theory is not Hermitian. However, it turns out to be P T symmetric. When one continues the theory into the complex plane and uses the P T symmetry inner product, viz. the overlap of the left-eigenstate of the Hamiltonian with its right-eigenstate, one then finds that for the vacuum this norm is both finite and positive, the Feynman rules now are valid, the Lorentzian path integral now is well behaved, and the theory now can serve as a low energy effective theory, one that we show to have a real classical gravity limit. Consequently, the theory can now be offered as a fully consistent, unitary and renormalizable theory of quantum gravity. [ABSTRACT FROM AUTHOR]

Flashover discharge occurs on spacecraft solar array with inverted potential gradient. The flashover discharges have been measured with an electron beam. However, it is difficult to charge the coupon surface uniformly. In this paper, ultraviolet light was used to achieve a uniform surface charging. The discharge current waveforms and surface potentials were measured with changing uniform surface potential. From these test results, the current waveform was calculated with a ladder circuit model. This model shows that the surface potential neutralization pattern is the same as that obtained with the experimental results. [ABSTRACT FROM PUBLISHER]

This contribution is a survey of the available experimental radiation data measured in the VUV range related to hypersonic atmospheric entry. The objective is to identify the datasets already gathered during aerothermodynamics studies for preparing Mars, Venus, and sample return missions. The final goal is to identify the most valuable datasets for comparisons with future data measured in the European shock-tube ESTHER. Due to the limited number of studies covering VUV radiation in relation to space exploration missions, the review has been extended to domains such as nuclear fusion, exobiology, chemical and process engineering. [ABSTRACT FROM AUTHOR]

Metamaterials and periodic structures operating under high-power excitations are susceptible to breakdown. It was recently demonstrated that a localized breakdown created in a given region of a periodic structure can facilitate breakdown in other regions of the structure where the intensity of the incident electromagnetic fields may not be high enough to cause breakdown under normal circumstances. It was also demonstrated that this phenomenon is due to the generation of vacuum ultraviolet radiation at the location of the initial discharge, which propagates to the neighboring regions (e.g., other unit cells in a periodic structure) and facilitates the generation of a discharge at a lower incident power level. In this paper, we present the results of an experimental study conducted to determine the effective range of this physical phenomenon for periodic structures that operate in air and in pure nitrogen gas at atmospheric pressure levels. It is demonstrated that when breakdown is induced in a periodic structure using a high-power pulse with a frequency of 9.382 GHz, duration of 0.8 is, and peak power level of 25 kW, this phenomenon is highly likely to happen in radii of approximately 16-17 mm from the location of the initial discharge under these test conditions. The results of this study are significant in designing metamaterials and periodic structures for high-power microwave applications as they suggest that a localized discharge created in such a periodic structure with a periodicity less than 16-17 mm can spread over a large surface and result in a distributed discharge. [ABSTRACT FROM AUTHOR]

Solvated electrons (eaq−) generated by atmospheric pressure plasmas in contact with liquids are a key source of plasma-induced liquid chemistry that enable applications in biotechnology and nanoparticle synthesis. In this paper, we report liquid phase reactive species concentrations near an anodic plasma-liquid interface as described by a fluid model. In particular, the interfacial structures and plasma-induced reactive species in NaCl and AgNO3 solutions as generated by a pulsed plasma are highlighted. The results show that the magnitude and the penetration depth of the eaq− concentration in AgNO3 solution are smaller than that in the NaCl solution due to the scavenger reactions of eaq− by Ag+ and NO3−. The early products of the plasma-induced Ag+ reduction are also presented, and the impact of the current density, the pulse width, and the AgNO3 concentration on the silver reduction is analyzed. It is further shown that a typical OH radical flux present in such plasmas can highly impact the eaq− concentration and the Ag+ reduction while the impact of vacuum ultraviolet radiation, H, and H2O2 is less pronounced. [ABSTRACT FROM AUTHOR]

To more efficiently develop the single-atom catalysis, it is essential to deeply characterize the single-atom catalysis structure and study their catalytic mechanisms at the molecular and atomic scale. Herein, this paper reviews the advanced techniques for charactering the structure of single-atom combustion catalysis, including synchrotron-radiation based X-ray absorption spectroscopy (XAS) and spherical aberration-collected transmission electron microscopy. Meanwhile, synchrotron-tradiation based operando and in-situ techniques are introduced, including XAS, Fourier transform infrared (EQIR) and synchrotron vacuum ultraviolet radiation photoionization mass spectrometry (SVUV-PIMS), which could play vital roles in unravelling the reaction mechanisms. These advanced structural characterizations to investigate the existence of single-atom catalysis and their catalytic mechanisms would significantly provide a new vision for the design and synthesis of single-atom combustion catalysis. Furthermore, current challenges and future research directions of these characterization techniques in single-atom combustion catalysis are presented. 38 References are included. [ABSTRACT FROM AUTHOR]

Free electron LASer in Hamburg is the first free electron laser user facility operating in the vacuum ultraviolet and soft X-ray wavelength range. Many user experiments require knowledge of the spatial and temporal coherence properties of the radiation. In this paper, we present a theoretical analysis of the coherence properties of the radiation for the fundamental and for the higher odd frequency harmonics. We show that temporal and spatial coherence reach their maxima close to the free electron laser (FEL) saturation but may degrade significantly in the post-saturation regime. We also find that the pointing stability of short FEL pulses is limited due to the fact that nonazimuthal FEL eigenmodes are not sufficiently suppressed. We discuss possible ways for improving the degree of transverse coherence and the pointing stability. [ABSTRACT FROM AUTHOR]

We have studied the electrical and optical characteristics of an air-cooled argon excimer vacuum-ultraviolet lamp (λ *** 126 nm) excited by a dielectric barrier discharge powered by: 1) pulsed or 2) sinusoidal high-voltage drivers from 32 to 100 kHz. Compared to sinusoidal excitation, pulsed excitation gives nearly *** 2x higher vacuum-ultraviolet (VUV) output and electrical-to-VUV conversion efficiency at high pressure (800-900 mbar). Visually, the pulse-driven plasma is spatially homogeneous, whereas for sinusoidal excitation the plasma becomes filamentary at higher pressure and/or frequency. Spectral emission is highly monochromatic with most of the output in the desired VUV band (λ = 115-140 nm). With the lamp running at pressure >700 mbar and power loadings >1.6 W/cm³, a sharp spike in VUV output was consistently seen at turn-on. We believe that transient phenomena or favorable initial conditions may be partly responsible for this VUV spike, although the equilibrium VUV output appears to be limited due to thermal dissipation, gas heating, and associated loss of gas from the active region. We propose that we may be observing the same intrinsic VUV spiking phenomena as reported in liquid nitrogen-cooled Xe, Kr, and Ar excimer lamps by Gerasimov et al. More importantly, we believe ours is the first such observation reported for an excimer VUV lamp operating near room temperature. This VUV spiking behavior raises the prospect that designs with improved thermal management may achieve even higher VUV power and efficiency. [ABSTRACT FROM AUTHOR]

The first stages of planet formation usually occur when the host star is still in a (relatively) dense star-forming region, where the effects of the external environment may be important for understanding the outcome of the planet formation process. In particular, star-forming regions that contain massive stars have strong far-ultraviolet (FUV) and extreme ultraviolet (EUV) radiation fields, which can induce mass-loss from protoplanetary discs due to photoevaporation. In this paper, we present a parameter-space study of the expected FUV and EUV fields in N -body simulations of star-forming regions with a range of initial conditions. We then use recently published models to determine the mass-loss due to photoevaporation from protoplanetary discs. In particular, we focus on the effects of changing the initial degree of spatial structure and initial virial ratio in the star-forming regions, as well as the initial stellar density. We find that the FUV fields in star-forming regions are much higher than in the interstellar medium, even when the regions have stellar densities as low as in the Galactic field, due to the presence of intermediate-mass, and massive, stars (>5 M⊙). These strong radiation fields lead to the destruction of the gas component in protoplanetary discs within 1 Myr, implying that gas giant planets must either form extremely rapidly (<1 Myr), or that they exclusively form in star-forming regions like Taurus, which contain no intermediate-mass or massive stars. The latter scenario is in direct tension with meteoritic evidence from the Solar system that suggests the Sun and its protoplanetary disc was born in close proximity to massive stars. [ABSTRACT FROM AUTHOR]

A laser-produced plasma source for extreme-ultraviolet (EUV) lithography conventionally uses a diffraction grating on the collection mirror for spectral purity filtering via diffractive scattering of infrared (IR) radiation. This paper proposes an alternative approach in which an EUV-blazed diffraction grating diverts in-band EUV radiation into the intermediate-focus aperture, rather than diverting IR out of the aperture. The full out-of-band spectrum, from long-wave IR to vacuum ultraviolet, can be fully excluded by this method regardless of whether the radiation is undiffracted or diffractively scattered by the grating. Much of the out-of-band radiation--especially the IR--is undiffracted, and this radiation can be efficiently returned to the plasma via retroreflection to enhance IR-to-EUV conversion. Plasma-emitted radiation that does not intercept the collection mirror can also be recycled back to the plasma via retroreflection to further boost EUV output. [ABSTRACT FROM AUTHOR]

In synchrotron radiation and electron storage rings, photon-stimulated gas desorption is a major contributor to gas load, leading to vacuum degradation and compromising the stability and quality of the beamline. Therefore, it is imperative to investigate the underlying mechanisms of photon-stimulated gas desorption to enhance the reliability of the experiments. In this paper, a theoretical model for analyzing the process of photon-stimulated desorption is presented, and the equations are solved numerically by considering the evacuation, bulk diffusion, thermal outgassing, adsorption, and desorption of surface gas molecules. The modified model can predict the yield of H 2 gas desorption induced by photon stimulation when synchrotron radiation is directed vertically onto various sample surfaces, utilizing the coupled multi-physics solution. The calculated results are consistent with the experimental measurements obtained from the Shanghai Synchrotron Radiation Facility. The results show that the photodesorption yield is related to the amount of surface-adsorbed molecules, which explains the observed decrease in the photodesorption yield with increasing accumulated photon dose. Furthermore, the study provides a theoretical approach to predicting the pressure evolution of photon-stimulated desorption. • A theoretical model for the analysis of photon-stimulated desorption (PSD) process is presented. • Reveals the mechanism underlying the decrease in the PSD yield with increasing accumulated photon dose. • Methods for predicting the evolution of pressure in the vacuum chamber before and after synchrotron radiation. • Methods for reducing the error between the tested PSD yield and the intrinsic PSD yield. [ABSTRACT FROM AUTHOR]

The low-lying electronic states of silicon dimer (Si 2 ) and its cation (Si 2 + ) have been studied by single-photon photoelectron spectroscopy combining a flow-tube reactor, vacuum-ultraviolet synchrotron radiation, and a double imaging photoelectron/photoion spectrometer. The energy range covered in this study (7.0−9.5 eV) allowed to observe several photoionising transitions involving the three lowest electronic states of Si 2 ( X 3 Σ g − , D 3 Π u , a 1 Δ g ) and five of the six lowest states of Si 2 + ( X + 4 Σ g − , a + 2 Π u , b + 2 Δ g , c + 2 Σ g − , and e + 2 Π u ). Using ab initio calculations and Franck-Condon simulations, several electronic transitions are identified which bring new elements in the description of the dense electronic landscapes of the silicon dimer and its cation. Interestingly, one of the most intense transitions is spin-forbidden ( X + 4 Σ g − ← a 1 Δ g ) and is most probably observed through autoionisation processes by spin interactions. [ABSTRACT FROM AUTHOR]

Highlights • SnTe as capping layer coatings in the vacuum and extreme ultraviolet spectral regions. • Design and fabrication of VUV quarter wave plates (QWP) based on SnTe/Al bilayer. • Extreme ultraviolet (EUV) improved facility for ellipsometric measurements. • Studying the polarimetric properties of SnTe/Al sample at the wavelength of (121.6 nm). • Angle-dependence phase retarder properties of SnTe/Al also reported in this study. Abstract Vacuum ultraviolet and extreme ultraviolet polarized light plays a significant role in many applications from materials science and solar physics investigations to optical components development. In this paper, we study the optical performances and the quarter wave retarder properties of aluminum coating capped with SnTe/Al thin film. The measurements have been performed by using a reflectometer properly improved for ellipsometric characterizations. The specimen has been fully characterized at hydrogen Lyman–alpha line (121.6 nm) by deriving the reflectance and the ellipsometric parameters, i.e. the ratio r and the phase difference δ. We found that the SnTe/Al bilayer behaves as phase retarder, although the performances differ from the ideal case. In fact, the polarimetric analysis combined with the optical test at different wavelengths allowed to identify carbon contamination on the top layer and a mild oxidation of the aluminum coating that affect the optical throughput. [ABSTRACT FROM AUTHOR]

This study employed a vacuum ultraviolet synchrotron radiation source and reflectron time‐of‐flight mass spectrometry (TOF‐MS) to investigate the photoionization and dissociation of styrene. By analyzing the photoionization mass spectrum and efficiency curve alongside G3B3 theoretical calculations, we determined the ionization energy of the molecular ion, appearance energy of fragment ions, and relevant dissociation pathways. The major ion peaks observed in the photoionization mass spectra of styrene correspond to C8H8+, C8H7+ and C6H6+. The ionization energy of styrene is measured as 8.46 ± 0.03 eV, whereas the appearance energies of C8H7+ and C6H6+ are found to be 12.42 ± 0.03 and 12.22 ± 0.03 eV, respectively, in agreement with theoretical values. The main channel for the photodissociation of styrene molecular ions is the formation of benzene ions, whereas the dissociation channel that loses hydrogen atoms is the secondary channel. Based on the experimental results and empirical formulas, the required dissociation energies (Ed) of C8H7+, C8H6+ and C6H6+ are calculated to be (3.96 ± 0.06), (4.00 ± 0.06) and (3.76 ± 0.06) eV, respectively. Combined with related thermochemical parameters, the standard enthalpies of formations of C8H8+, C8H7+, C8H6+ and C6H6+ are determined to be 964.2, 1346.3, 1350.2 and 1327.0 kJ/mol, respectively. Based on the theoretical study, the kinetic factors controlling the styrene dissociation reaction process are determined by using the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This provides a reference for further research on the atmospheric photooxidation reaction mechanism of styrene in atmospheric and interstellar environments. [ABSTRACT FROM AUTHOR]

Results are presented of research aimed at creating a compact source of soft X-ray and vacuum ultraviolet radiation through the collision of a powerful plasma flow with a gas jet. In experiments that were carried out, a pulsed electrodynamic accelerator generated a hydrogen plasma flow with an energy constant of ≈50 kJ and duration of 10–15 μs. The flow, with a density of ≈6 × 1015 cm–3, moved at a velocity of (2‒4) × 107 cm/s in a longitudinal magnetic field with an induction of up to 2 T and interacted with a flat supersonic gas jet. The maximum molecular density of the gas, nitrogen or neon, in the jet reached 1017 cm–3. The formation of a compact emitting plasma layer with a thickness of 3–5 cm, moving along the path of the hydrogen plasma flow at a speed of approximately 3 × 106 cm/s was demonstrated. In several experiments, a tungsten plate was used as an obstacle to confine the motion of the emitting plasma along the magnetic field, localizing the interaction region between the plasma flow and the gas jet within the diagnostic control zone. Soft X-ray obscurography and spectroscopy were used to obtain data regarding the radiation generation from the interaction zone of the hydrogen plasma flow and the gas jet. The results of measuring the radiation energy from the formed plasma are presented: ≈2 kJ in the case of a nitrogen jet and ≈ 3 kJ in the case of a neon jet. Numerical modeling of the line radiation from multi-charged ions and subsequent comparison of calculated and experimental data allowed estimating the electron temperature of the nitrogen and neon plasmas formed during the interaction of the hydrogen plasma flow with the gas jet at a level of ≥40 eV. [ABSTRACT FROM AUTHOR]

Carbon 1s excitation of methane, CH4, has been studied in the gas phase using the ion trap integrated with the photon–ion instrument at PETRA III/DESY and soft X-rays from the beamline P04. The created photoions are stored within the ion trap so that in further steps the photoions can undergo reactions with neutral methane molecules. The ionic photoproducts as well as reaction products created thereby are mass-over-charge analyzed by an ion time-of-flight spectrometer. Besides the photoions, product ions with up to three carbon atoms are found. In contrast to experiments using vacuum ultraviolet radiation, especially highly reactive product ions with a small number of hydrogen atoms such as C 2 H 2 + and C 2 H 3 + are found, which are important precursors for larger hydrocarbons such as C6H6. Possible production routes of the product ions are analyzed on the basis of a model that considers the probabilities for photofragmentation and the first subsequent chemical reaction step. The model indicates that the high degree of fragmentation by photons with energies around 280 eV is favoring these products. The results of the measurements show that the products like C 2 H 2 + and C 2 H 3 + can be generated by a single collision of the ionization product with neutral methane. The results suggest that soft X-rays might be important for chemical reactions in planetary atmospheres, which has usually not been taken into account. However, due to the high degree of fragmentation and large cross sections involved, they can have a large influence even when the corresponding photon flux is rather small. [ABSTRACT FROM AUTHOR]

The C2 carbon cluster is found in a large variety of environments including flames, electric discharges, and astrophysical media. Due to spin-selection rules, assessing a complete overview of the dense vibronic landscape of the C 2 + cation starting from the ground electronic state X Σ g + 1 of the neutral is not possible, especially since the C 2 + ground state is of X + Σ g − 4 symmetry. In this work, a flow-tube reactor source is employed to generate the neutral C2 in a mixture of both the lowest singlet X Σ g + 1 and triplet a 3Πu electronic states. We have investigated the vibronic transitions in the vicinity of the first adiabatic ionization potential via one-photon ionization with vacuum ultraviolet synchrotron radiation coupled with electron/ion double imaging techniques. Using ab initio calculations and Franck-Condon simulations, three electronic transitions are identified and their adiabatic ionization energy is determined E i ( a + 2 Π u ← X 1 Σ g + ) = 12.440 (10) eV, E i ( X + 4 Σ g − ← a 3 Π u ) = 11.795 (10) eV, and Ei(a+2Πu ← a3Πu) = 12.361(10) eV. From the three origin bands, the following energy differences are extracted: ΔE(a − X) = 0.079(10) eV and ΔE(a+ − X+) = 0.567(10) eV. The adiabatic ionization potential corresponding to the forbidden one-photon transition X+ ← X is derived and amounts to 11.873(10) eV, in very good agreement with the most recent measurement by Krechkivska et al. [J. Chem. Phys. 144, 144305 (2016)]. The enthalpy of formation of the doublet ground state C 2 + cation in the gas phase is determined at 0 K, Δ f H 0 (0 K) ( C 2 + ( Π u 2 )) = 2019.9 (10) kJ mol−1. In addition, we report the first experimental ion yield of C2 for which only a simple estimate was used up to now in the photochemistry models of astrophysical media due to the lack of experimental data. [ABSTRACT FROM AUTHOR]

The materials of the article outline the features of the use of ultraviolet LED systems in industry, and propose a solution for their use in the grain processing and compound feed industry. Ultraviolet light (UV) is a well-researched and widely used means of decontamination and disinfection of surfaces, air, water, and food. Usually, far ultraviolet radiation (or ultraviolet C, UVC) with a wavelength of 254 nm is used, which corresponds to the peak absorption of wave energy by the DNA of a living cell. There is a mathematical mechanism for calculating the parameters of radiation in relation to its effect on microorganisms: a curve describing the microbial death depending on the increase in the radiation dose received by the bacteria and formulae for the relationship between the three main parameters (dose, radiation flux and exposure duration). Ultraviolet lamps (tubes) are commonly used, on the basis of which a large number of emitters have been developed for different needs. There are also emitters for grain and feed disinfection in use, but only outside of industrial production lines. Ultraviolet irradiation is not used directly on manufacturing lines so far. However, it can be used to reduce the microbial burden of a feed or food product prior to packaging the finished product. For this purpose, ultraviolet light-emitting diodes (LEDs) available on the world market today can be used. However, their use faces difficulties: ultraviolet LEDs emit wavelengths longer than lamps (at about 275 nm or more), which requires an increase in the duration of irradiation, which is undesirable for industrial processing of products directly on the line. However, the small size of the UVC LEDs will allow them to be installed in grain processing and feed mills inside equipment (magnetic separators, gravity feeders, etc.) with appropriate protection against damage by moving material. In addition, suspended emitters of any configuration can be placed above belt conveyors that move material at a certain speed. This approach will require certain measures to control the efficiency of irradiation (requires microbiological studies) and to protect personnel from the harmful effects of ultraviolet rays (means of personal and collective protection, measurement of radiation intensity). [ABSTRACT FROM AUTHOR]

This paper describes a method for transferring a nanoscale pattern from a cyclic olefin polymer (COP) mold to the surface of UV curable polydimetylsiloxane (PDMS) on a glass substrate. The PDMS is first deposited on the patterned mold by spin-coating and photocuring. Vacuum ultraviolet (VUV) radiation is then used to activate the surface of both the PDMS and the glass substrate before bringing them into contact. Once a bond has been formed, the COP mold is peeled away, leaving the patterned PDMS on the glass substrate. Bonding tests were first carried out to determine the optimum VUV irradiation dose to form a permanent bond. The effectiveness of the proposed method was then demonstrated by transferring a periodic nanoscale pattern. Microscopic examination of the original and transferred patterns revealed that successful reproduction was achieved. A spectroscopic analysis was also performed to clarify the mechanism involved in the bonding process. The results suggested that VUV irradiation caused oxidation of the PDMS surface and the formation of OH groups. When the PDMS and the glass substrate were brought into contact, a dehydration reaction took place which caused the formation of siloxane ( O Si O ) bonds between the two materials. The proposed method offers the advantages of being simple and allowing deformation-free transfer of very fine patterns. It can also be applied to a wide range of nanoscale fabrication tasks. [ABSTRACT FROM AUTHOR]

The present paper is focused on the use of a vacuum ultraviolet absorption spectrometer (VUV) for gas chromatography (GC), within the context of flow modulated comprehensive two-dimensional gas chromatography (FM GC × GC). The features of the VUV detector were evaluated through the analysis of petrochemical and fatty acids samples. Besides responding in a predictable fashion via Beer’s law principles, the detector provides additional spectroscopic information for qualitative analysis. Virtually all chemical species absorb and have unique gas phase absorption features in the 120–240 nm wavelength range monitored. The VUV detector can acquire up to 90 full range absorption spectra per second, allowing its coupling with comprehensive two-dimensional gas chromatography. This recent form of detection can address specific limitations related to mass spectrometry ( e.g., identification of isobaric and isomeric species with very similar mass spectra or labile chemical compounds), and it is also able to deconvolute co-eluting peaks. Moreover, it is possible to exploit a pseudo-absolute quantitation of analytes based on pre-recorded absorption cross-sections for target analytes, without the need for traditional calibration. Using this and the other features of the detector, particular attention was devoted to the suitability of the FM GC × GC-VUV system toward qualitative and quantitative analysis of bio-diesel fuel and different kinds of fatty acids. Satisfactory results were obtained in terms of tailing factor (1.1), asymmetry factor (1.1), and similarity (average value 97%), for the FAMEs mixtures analysis. [ABSTRACT FROM AUTHOR]

There is growing theoretical and observational evidence that protoplanetary disc evolution may be significantly affected by the canonical levels of far-ultraviolet (FUV) radiation found in a star-forming environment, leading to substantial stripping of material from the disc outer edge even in the absence of nearby massive stars. In this paper, we perform the first full radiation hydrodynamic simulations of the flow from the outer rim of protoplanetary discs externally irradiated by such intermediate strength FUV fields, including direct modelling of the photon-dominated region which is required to accurately compute the thermal properties. We find excellent agreement between our models and the semi-analytic models of Facchini et al. (2016) for the profile of the flow itself, as well as the mass-loss rate and location of their 'critical radius'. This both validates their results (which differed significantly from prior semianalytic estimates) and our new numerical method, the latter of which can now be applied to elements of the problem that the semi-analytic approaches are incapable of modelling. We also obtain the composition of the flow, but given the simple geometry of our models we can only hint at some diagnostics for future observations of externally irradiated discs at this stage. We also discuss the potential for these models as benchmarks for future photochemical-dynamical codes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We proposed and demonstrated an optical dry etching method for transferring a pattern on a photomask to a surface of plastics by decomposing the irradiated area using the high energy of vacuum ultraviolet light (VUV) at room temperature and pressure. Two kinds of wavelengths of 160 nm and 172 nm were used as the vacuum ultraviolet light, and the patterning performances for polymethyl methacrylate (PMMA) and polycarbonate (PC) were compared. As a result, it was revealed that proportional relationships were obtained between the etching rate and the irradiation dose for both wavelengths, and the cross-sectional profiles were anisotropic. In addition, both PMMA and PC were etched at a wavelength of 160 nm, whereas PC could not be etched at a wavelength of 172 nm, suggesting that it correlates with the bond dissociation energies of the molecular bonds of the materials and the energies of the photons. Furthermore, by combining this method with the optical bonding method that we had previously developed to bond surfaces irradiated with VUV, we have demonstrated a method for fabricating microfluidic devices by irradiating only with VUV. This paper shows that this technique is a new microfabrication method suitable for simple and mass production of plastic materials. [ABSTRACT FROM AUTHOR]

This work presents a computational study of the atmospheric pressure plasma of the COST jet source in He + 0.1% N2 buffer gas, incorporating the treatment of the VUV resonant radiation from He atoms at a wavelength of 58.4 nm. The plasma is driven by single- and multi-frequency waveforms at various peak-to-peak voltages between 400 V and 685 V. The simulations, which include the photoemission of electrons from the electrodes as well as the photoionization of the N2 molecules indicate that these processes, induced by the VUV radiation, have relatively little influence on the discharge characteristics due to other more efficient charged particle production mechanisms, e.g., Penning ionization. While the plasma characteristics are computed along one spatial dimension perpendicular to the electrodes, the tracing of the VUV photons is executed in the real 3D geometry of the plasma source to allow the computation of the VUV photon flux leaving the device through the orifice. Photon fluxes up to ≈ 5 Ă— 1 0 15 cmâˆ'2 sâˆ'1, corresponding to an energy flux of ≈18 mW cmâˆ'2 are found at multi-frequency operation. [ABSTRACT FROM AUTHOR]

The paper has investigated the process of measuring power illumination for vacuum ultraviolet radiation by means of the solution of potassium iodide as a photochemical actinometer. We have investigated the formation of triiodide-ion when radiated the solution of light with wavelength 185 nm. It has been shown that obtaining hydroxyl radicals OH at this wavelength is determined by the formation of I. The quantum yield of the process constitutes 0.165. Measuring the concentration of the obtained I we determined power illumination of a quartz lamp DRB-20 (wavelength 185 nm), which constitutes 49.2 × 10 E/s. [ABSTRACT FROM AUTHOR]

The luminescent properties of LSO:Ce (1 mol%) scintillators were characterized systematically under vacuum ultraviolet (VUV)–UV excitation. Under 185 nm VUV excitation, a broad emission band was detected in the wavelength range from 350 nm to 600 nm at different temperatures, which is ascribed to the 5d→4f electron transitions of Ce 3+ . Excitation wavelength and temperature effects on luminescent properties of LSO:Ce ceramic scintillators were investigated in this paper. At 50 K, the emission intensity of Ce1 (Ce 3+ locating in seven-oxygen-coordinated site) was much stronger than that of Ce2 (Ce 3+ locating in six-oxygen-coordinated site), and the total emission intensity excited by 355 nm (Ce1) was higher than that excited by 185 nm (host). The total luminescence intensity increases as the rising temperature in the temperature range of 150–300 K, which is originated from thermal enhancement of transportation of free carriers dominating Ce1 emission. [ABSTRACT FROM AUTHOR]

A new monochromator scheme is presented in which an extra-focus constant-included-angle varied-line-spacing cylindrical-grating monochromator (extra-focus CIA-VCGM) is conveniently combined with a variable-included-angle varied-line-spacing plane-grating monochromator (VIA-VPGM). This dual-mode solution delivers high performance in the energy range from vacuum ultraviolet (VUV) to soft X-ray. The resolving power and the efficiency of this dual-mode grating monochromator are analyzed in detail based on realistic parameters. Comparisons with the commonly used variable-included-angle plane-grating monochromator and normal-incidence monochromator (VIA-PGM/NIM) hybrid monochromator are made. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet (VUV) spectrum for CH2F2 from a new synchrotron study has been combined with earlier data and subjected to detailed scrutiny. The onset of absorption, band I and also band IV, is resolved into broad vibrational peaks, which contrast with the continuous absorption previously claimed. A new theoretical analysis, using a combination of time dependent density functional theory (TDDFT) calculations and complete active space self-consistent field, leads to a major new interpretation. Adiabatic excitation energies (AEEs) and vertical excitation energies, evaluated by these methods, are used to interpret the spectra in unprecedented detail using theoretical vibronic analysis. This includes both Franck-Condon (FC) and Herzberg-Teller (HT) effects on cold and hot bands. These results lead to the re-assignment of several known excited states and the identification of new ones. The lowest calculated AEE sequence for singlet states is 11B1 ∼ 11A2 < 21B1 < 11A1 < 21A1 < 11B2 < 31A1 < 31B1. These, together with calculated higher energy states, give a satisfactory account of the principal maxima observed in the VUV spectrum. Basis sets up to quadruple zeta valence with extensive polarization are used. The diffuse functions within this type of basis generate both valence and low-lying Rydberg excited states. The optimum position for the site of further diffuse functions in the calculations of Rydberg states is shown to lie on the H-atoms. The routine choice on the F-atoms is shown to be inadequate for both CHF3 and CH2F2. The lowest excitation energy region has mixed valence and Rydberg character. TDDFT calculations show that the unusual structure of the onset arises from the near degeneracy of 11B1 and 11A2 valence states, which mix in symmetric and antisymmetric combinations. The absence of fluorescence in the 10.8–11 eV region contrasts with strong absorption. This is interpreted by the 21B1 and 11A1 states where no fluorescence is calculated for these two states, which are only active in absorption. The nature of the two states, 11B1 and 21B1, is fundamentally different, but both are complex owing to the presence of FC and HT effects occurring in different ways. The two most intense bands, close to 12.5 and 15.5 eV, contain valence states as expected; the onset of the 15.5 eV band shows a set of vibrational peaks, but the vibration frequency does not correspond to any of the photoelectron spectral (PES) structure and is clearly valence in nature. The routine use of PES footprints to detect Rydberg states in VUV spectra is shown to be inadequate. The combined effects of FC and HT in the VUV spectral bands lead to additional vibrations when compared with the PES. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The electronic absorption spectrum of N,N-dimethylformamide (DMF) is studied in the 45 000-80 000 cm-1 (5.6-9.9 eV) region using synchrotron radiation. The vacuum ultraviolet (VUV) spectrum comprises mostly of Rydberg series of ns, np, and nd types converging to the first two ionization potentials (IPs). Quantum defect values obtained are consistent with excitation of an electron from the highest occupied molecular orbitals localized on nitrogen (4a″) and oxygen (16a′); in addition, the 3s Rydberg transition converging to the third IP (3a″) is observed at 8.95 eV. A reinvestigation of the infrared spectrum of DMF in the 500-4000 cm-1 region with the help of density functional theory (DFT) calculations establishes the planarity of the ground state and leads to revision of several vibrational assignments. Vertical excited state energies and their valence/Rydberg character are predicted using time dependent DFT calculations; excellent correlation is achieved between theoretical results and experimentally observed spectral features. Potential energy curves of the first few excited states give additional insights into the nature of the excited states and their role in photodissociation dynamics. The absorption spectrum of DMF in the region >63 400 cm-1 (7.85 eV) as well as a complete set of spectral assignments in the VUV region (45 000-80 000 cm-1) is reported for the first time. This work represents a comprehensive study of the absorption spectra of DMF in the VUV and infrared regions. [ABSTRACT FROM AUTHOR]

The production of phosphoryl species (PO, PO2, HOPO) is believed to be of great importance for efficient flame-retardant action in the gas phase. We present a detailed investigation of the thermal decomposition of dimethyl methylphosphonate (DMMP) probed by vacuum ultraviolet (VUV) synchrotron radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. This technique provides a snapshot of the thermolysis process and direct evidence of how the reactive phosphoryl species are generated during heat exposure. One of the key findings of this work is that only PO is formed in high concentration upon DMMP decomposition, whereas PO2 is absent. It can be concluded that the formation of PO2 needs an oxidative environment, which is typically the case in a real flame. Based on the identification of products such as methanol, formaldehyde, and PO, as well as the intermediates OPCH3, H2CPOH, and H2CP(O)H, supported by quantum chemical calculations, we were able to describe the predominant pathways that lead to active phosphoryl species during the thermal decomposition of DMMP. [ABSTRACT FROM AUTHOR]

A high resolution vacuum ultraviolet (HRVUV) beamline based on a 6.65 m off-plane Eagle spectrometer is in operation at the Indus-1 synchrotron radiation source, RRCAT, Indore, India. To facilitate position sensitive detection and fast spectral recording, a new BaFBr:Eu 2+ phosphor based image plate (IP) detection system interchangeable with the existing photomultiplier (PMT) scanning system has been installed on this beamline. VUV photoabsorption studies on Xe, O 2 , N 2 O and SO 2 are carried out to evaluate the performance of the IP detection system. An FWHM of ~0.5 Å is achieved for the Xe atomic line at 1469.6 Å. Reproducibility of spectra is found to be within the experimental resolution. Compared to the PMT scanning system, the IP shows several advantages in terms of sensitivity, recording time and S / N ratio, which are highlighted in the paper. This is the first report of incorporation of an IP detection system in a VUV beamline using synchrotron radiation. Commissioning of the new detection system is expected to greatly enhance the utilization of the HRVUV beamline as a number of spectroscopic experiments which require fast recording times combined with a good signal to noise ratio are now feasible. [ABSTRACT FROM AUTHOR]

• First systematic experimental study of OME oxidation with different chain lengths. • Species pool is dominated by oxygenates and nearly independent of the chain length. • Highest oxygenated intermediate of OME 1-5 combustion is methyl formate. • Reactivity: shift of the intermediate's peak for longer OMEs to lower temperatures. • Significant fractions of ethanol detected using photoionization spectroscopy. This paper presents a systematic study of oxymethylene ethers (OMEs) oxidation in an atmospheric laminar flow reactor setup. Oxymethylene ethers with different number of oxymethylene ether groups (n = 0–5) have been investigated under lean and rich conditions (750–1250 K). The flow reactor is coupled to an electron ionization molecular-beam mass spectrometer (EI-MBMS) with high mass resolution to measure speciation data. Additional isomer-selective speciation analysis was performed using a novel atmospheric laminar flow reactor combined with double-imaging photoelectron photoion coincidence (i2PEPICO) spectroscopy at the vacuum ultraviolet radiation (VUV) beamline of the Swiss Light Source. The results show a dominance of oxygenated intermediates during the combustion of all OMEs in the investigated temperature regime. The observed species pool is thereby nearly independent of the OME's chain length. In particular the presence of significant fractions of ethanol is remarkable and indicates unknown or underestimated reaction pathways to form C–C bonds from OME structures. Formation of combustion intermediates during oxidation of longer OMEs occurs at lower temperatures and correlates with the ignition delay time. No hydrocarbons with more than four carbon atoms are detected. The combination of high mass resolution provided by EI-MBMS detection and isomer-selective analysis by i2PEPICO enables a complete overview of all intermediates. This allows for in-depth discussion and analysis of systematic trends for several intermediate species. [ABSTRACT FROM AUTHOR]

We investigate the laser ionization process taking place when the CO molecule is exposed to vacuum ultraviolet (VUV) radiation resonant with the CO A¹Π(v = 0) ← X¹Σ+(v = 0) transition around 154 nm, along with the ultraviolet (UV) and visible (Red) radiation used to generateVUVby four-wave difference-frequency mixing. By measuring the CO+ ion recoil and a room temperature gas spectrum, it is possible to assign the ionization process as 1 + 1′ + 1″ REMPI where the one-photon steps refer to the VUV, UV, and Red radiation, respectively. Resonance enhanced ionization of rotational states around J = 12 arise due to the overlap of the fixed wavelength UV (∼250 nm) with the R band-head of a transition assigned to CO E¹Π(v = 6) ← A¹Π(v = 0) with a term value of 104 787.5 cm-1. The REMPI process is efficient and polarization sensitive and should be useful in a wide range of studies involving nascent CO. [ABSTRACT FROM AUTHOR]

Vacuum ultraviolet (VUV) radiation emitted by microwave driven argon plasmas has been investigated at low-pressure conditions (0.36 mbar). A classical surface-wave sustained discharge at 2.45 GHz has been used as plasma source. VUV radiation has been detected by emission spectroscopy in the 30-125 nm spectral range. The spectrum exhibits atomic and ionic argon emissions with the most intense spectral lines corresponding to the atomic resonance lines, at 104.8 nm and 106.7 nm, and to the ion lines, at 92.0 nm and 93.2 nm. Emissions at lower wavelengths were also detected, including lines with no information concerning level transitions in the well-known NIST database (e.g., the atomic line at 89.4 nm). The dependence of the lines' intensity on the microwave power delivered to the launcher was investigated. The electron density was estimated to be around 1012 cm-3 using the Stark broadening of the hydrogen Hβ line at 486.1 nm. The main population and loss mechanisms considered in the model for the excited argon atom and ion states emitting in the VUV range are discussed. The experimental results were compared to self-consistent model predictions, and a good agreement was obtained. [ABSTRACT FROM AUTHOR]

Over decades, sunspots and their fine structures have been studied in detail at the photospheric level with different ground-based telescopes, as the surface of the Sun primarily emits light in the visible wavelengths. For a very long period, the upper atmosphere above the sunspot regions, especially the transition region (TR) above sunspots where the plasma emits light in the far ultraviolet (FUV) and extreme ultraviolet (EUV), has been poorly understood. In the past decades after the development of space instrumentations, FUV and EUV observations have uncovered many secrets of the TR above sunspots. In this paper, we present a brief review of research results about the TR structures and dynamics obtained through imaging and spectroscopic observations of sunspots in the past ~ 20 years. Though these observations have gathered remarkable and detailed information and greatly improved our understanding of the TR above the sunspots, paradoxically, they leave us with many new questions which should be answered in the future. [ABSTRACT FROM AUTHOR]

Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge. [ABSTRACT FROM AUTHOR]

We have designed a silicon detector based on an avalanche photodiode for detecting vacuum ultraviolet radiation. It was demonstrated that the detector has a photon detection efficiency superior to 0.65 electrons / photon, in the wavelength range from 114 to 170 nm, with an external quantum yield from 49 to 7000 electrons / photon at a reverse-bias voltage from 190 to 315 V, respectively. The detector's active area diameter is 1.5 mm. [ABSTRACT FROM AUTHOR]

High-harmonic generation is a cornerstone of nonlinear optics. It has been demonstrated in dielectrics, semiconductors, semi-metals, plasmas, and gases, but, until now, not in metals. Here we report high harmonics of 800-nm-wavelength light irradiating metallic titanium nitride film. Titanium nitride is a refractory metal known for its high melting temperature and large laser damage threshold. We show that it can withstand few-cycle light pulses with peak intensities as high as 13 TW/cm2, enabling high-harmonics generation up to photon energies of 11 eV. We measure the emitted vacuum ultraviolet radiation as a function of the crystal orientation with respect to the laser polarization and show that it is consistent with the anisotropic conduction band structure of titanium nitride. The generation of high harmonics from metals opens a link between solid and plasma harmonics. In addition, titanium nitride is a promising material for refractory plasmonic devices and could enable compact vacuum ultraviolet frequency combs. High harmonic generation is a nonlinear optical phenomena and HHG from solid offers challenges and advantages over dilute media like gases. Here the authors report HHG from metallic thin film of titanium nitride and discuss the role of intraband current to HHG. [ABSTRACT FROM AUTHOR]

Identification of many Rydberg states in iodobenzene, especially from the first and fourth ionization energies (IE1 and IE4, X²B1 and C²B1), has become possible using a new ultraviolet (UV) and vacuum-ultraviolet (VUV) absorption spectrum, in the region 29 000-87 000 cm&#-1; (3.60-10.79 eV), measured at room temperature with synchrotron radiation. A few Rydberg states based on IE2 (A²A2) were found, but those based on IE3 (B²B2) are undetectable. The almost complete absence of observable Rydberg states relating to IE2 and IE3 (A²A2 and B²B2, respectively) is attributed to them being coupled to the near-continuum, high-energy region of Rydberg series converging on IE1. Theoretical studies of theUVandVUVspectra used both time-dependent density functional (TDDFT) and multi-reference multi-root doubles and singles-configuration interaction methods. The theoretical adiabatic excitation energies, and their corresponding vibrational profiles, gave a satisfactory interpretation of the experimental results. The calculations indicate that the UV onset contains both 1¹B1 and 1¹B2 states with very low oscillator strength, while the 2¹B1 state was found to lie under the lowest ππ* 1¹A1 state. All three of these ¹B1 and ¹B2 states are excitations into low-lying σ* orbitals. The strongest VUV band near 7 eV contains two very strong ππ* valence states, together with other weak contributors. The lowest Rydberg 4b16s state (3¹B1) is very evident as a sharp multiplet near 6 eV; its position and vibrational structure are well reproduced by the TDDFT results. [ABSTRACT FROM AUTHOR]

Ultraviolet photons can damage microorganisms, which rarely survive prolonged irradiation. In addition to the need for intact DNA, cell viability is directly linked to the functionality of the cell wall and membrane. In this work, Cladosporium herbarum spore monolayers exhibit high viability (7%) when exposed to 157 nm laser irradiation (412 kJm-2) or vacuum-ultraviolet irradiation (110-180 nm) under standard pressure and temperature in a nitrogen atmosphere. Spore viability can be determined by atomic-force microscopy, nano-indentation, mass, μ-Raman and attenuated reflectance Fourier-transform far-infrared spectroscopies and DNA electrophoresis. Vacuum ultraviolet photons cause molecular damage to the cell wall, but radiation resistance in spores arises from the activation of a photon-triggered signaling reaction, expressed via the exudation of intracellular substances, which, in combination with the low penetration depth of vacuum-ultraviolet photons, shields DNA from radiation. Resistance to phototoxicity under standard conditions was assessed, as was resistance to additional environmental stresses, including exposure in a vacuum, under different rates of change of pressure during pumping time and low (10 K) temperatures. Vacuum conditions were far more destructive to spores than vacuum-ultraviolet irradiation, and UV-B photons were two orders of magnitude more damaging than vacuum-ultraviolet photons. The viability of irradiated spores was also enhanced at 10K. This work, in addition to contributing to the photonic control of the viability of microorganisms exposed under extreme conditions, including decontamination of biological warfare agents, outlines the basis for identifying bio-signaling in vivo using physical methodologies. [ABSTRACT FROM AUTHOR]

The photoionization and dissociative photoionization of o-xylene have been studied using synchrotron radiation vacuum ultraviolet light with the photon energy in the range of 8.0–13.0 eV. The ionization energy of o-xylene and the appearance energies for the main fragment ions C 8 H 9 + , C 7 H 7 + and C 6 H 6 + were determined to be 8.45, 11.08, 11.47 and 11.17 eV, respectively, with photoionization efficiency spectra (PIES). Three dissociation pathways of parent ions are investigated by experimental photoionization and the quantum-chemical calculations. The fragment ions C 7 H 7 + derived from parent ions involved hydrogen atom transfer rather than direct dissociation. Particularly, detailed mechanisms of dissociation C 6 H 6 + are presented for the first time in this work. In addition, the geometries of the intermediates (INTs), transition states (TSs) and products have been performed at B3LYP/6-311 + + G (d, p) level. The mechanisms of dissociative photoionization of o-xylene and the INTs and TSs involved are discussed in detail. [ABSTRACT FROM AUTHOR]

Biofuels are a promising ecologically viable and renewable alternative to petroleum fuels, with the potential to reduce net greenhouse gas emissions. However, biomass sourced fuels are often produced as blends of hydrocarbons and their oxygenates. Such blending complicates the implementation of these fuels in combustion applications. Variations in a biofuel's composition will dictate combustion properties such as auto ignition temperature, reaction delay time, and reaction pathways. A handful of novel drop-in replacement biofuels for conventional transportation fuels have recently been down selected from a list of over 10,000 potential candidates as part of the U.S. Department of Energy's (DOE) Co-Optimization of Fuels and Engines (Co-Optima) initiative. Diisobutylene (DIB) is one such high-performing hydrocarbon which can readily be produced from the dehydration and dimerization of isobutanol, produced from the fermentation of biomass-derived sugars. The two most common isomers realized, from this process, are 2,4,4-trimethyl-1-pentene (α-DIB) and 2,4,4-trimethyl-2-pentene (β-DIB). Due to a difference in olefinic bond location, the α- and β- isomer exhibit dramatically different ignition temperatures at constant pressure and equivalence ratio. This may be attributed to different fragmentation pathways enabled by allylic versus vinylic carbons. For optimal implementation of these biofuel candidates, explicit identification of the intermediates formed during the combustion of each of the isomers is needed. To investigate the combustion pathways of these molecules, tunable vacuum ultraviolet (VUV) light (in the range 8.1–11.0 eV) available at the Lawrence Berkeley National Laboratory's Advanced Light Source (ALS) has been used in conjunction with a jet stirred reactor (JSR) and time-of-flight mass spectrometry to probe intermediates formed. Relative intensity curves for intermediate mass fragments produced during this process were obtained. Several important unique intermediates were identified at the lowest observable combustion temperature with static pressure of 93,325 Pa and for 1.5 s residence time. As this relatively short residence time is just after ignition, this study is targeted at the fuels' ignition events. Ignition characteristics for both isomers were found to be strongly dependent on the kinetics of C4 and C7 fragment production and decomposition, with the tert-butyl radical as a key intermediate species. However, the ignition of α-DIB exhibited larger concentrations of C4 compounds over C7, while the reverse was true for β-DIB. These identified species will allow for enhanced engineering modeling of fuel blending and engine design. [ABSTRACT FROM AUTHOR]

The luminescent properties of Ca3TaGa3Si2O14 (CTGS, catangasite) single crystals have been studied by means of the vacuum ultraviolet excitation spectroscopy utilizing synchrotron radiation from 1.5 GeV storage ring of MAX IV synchrotron facility. Two emission bands at 320 nm (3.87 eV) and 445 nm (2.78 eV) have been detected. Examining excitation spectra in vacuum ultraviolet spectral range, the 320 nm emission band was explained as the emission band of self-trapped exciton in CTGS single crystal. Its atomic structure is discussed. It is also proposed that the 445 nm (2.78 eV) emission in the CTGS is due to the F centers, which have shown a well-resolved excitation (absorption) band at 5.1 eV (243 nm). [ABSTRACT FROM AUTHOR]

Low-pressure (a few to hundreds of millitorrs) inductively coupled plasmas (ICPs), as typically used in microelectronics fabrication, often produce vacuum-ultraviolet (VUV) photon fluxes onto surfaces comparable to or exceeding the magnitude of ion fluxes. These VUV photon fluxes are desirable in applications such as sterilization of medical equipment but are unwanted in many materials fabrication processes due to damage to the devices by the high-energy photons. Under specific conditions, VUV fluxes may stimulate etching or synergistically combine with ion fluxes to modify polymeric materials. In this regard, it is desirable to control the magnitude of VUV fluxes or the ratio of VUV fluxes to those of other reactive species, such as ions, or to discretely control the VUV spectrum. In this paper, we discuss results from a computational investigation of VUV fluxes from low-pressure ICPs sustained in rare gas mixtures. The control of VUV fluxes through the use of pressure, pulsed power, and gas mixture is discussed. We found that the ratio, β, of VUV photon to ion fluxes onto surfaces generally increases with increasing pressure. When using pulsed plasmas, the instantaneous value of β can vary by a factor of 4 or more during the pulse cycle due to the VUV flux more closely following the pulsed power. [ABSTRACT FROM AUTHOR]

• Vacuum UV photoabsorption spectrum of trans-1,2-C 2 H 2 Cl 2 for the first time between 5.0 eV and 20.0 eV. • Analysis of electronic and vibrational Rydberg transitions. • Detailed analysis for the first time of the valence transitions. • Interpretation and assignments based on quantum chemical calculations. This paper investigates in detail the vacuum UV photoabsorption spectrum of trans-1,2-C 2 H 2 Cl 2 in the 5–20 eV range using synchrotron radiation. Quantum chemical calculations are applied to the electronic transitions. Particular attention has been paid to the 2a u (π)→2b g (π*) transition included in the broad band observed at 6.30 eV. The Rydberg 2a u (π)→R3s transition is presumably observed at 6.27 eV. Below 6.0 eV the structure(s) are assigned to π→σ* transition(s). The abundantly structured spectrum observed between 7.0 eV and 12.0 eV has been analyzed in terms of vibronic transitions to ns- (δ ¯ =0.844) and nd/4f- (δ ¯ =0.03/0.011) Rydberg states, converging to the 2a u −1 ionization continuum, to two series of np- (δ ¯ = 0.66 and 0.40) states converging to the 5a g −1 continuum, to ns- (δ ¯ =0.983) and nd- (δ ¯ = –0.06) states converging to the 4b u −1 continuum and to two np-type (δ ¯ = 0.51 and 0.26) series converging to the 1b g −1 continuum. These data are complemented by an analysis of the vibrational structure of the individual Rydberg states. Comparisons with previously reported values are provided. Several other spectral features Table S2 (see Supplementary Material) in the 12–20 eV range are tentatively assigned to transitions to Rydberg states converging to higher ionic excited states of trans-1,2-C 2 H 2 Cl 2. Assignments of the vibrational structure of some of these transitions are also proposed. [ABSTRACT FROM AUTHOR]