OH Band Research Articles

The fate of ammonium in phengite at high temperature

Nitrogen (N) is the main component of the atmosphere and is largely considered as a volatile element. However, most researchers now agree that a significant amount of N, in the form of ammonium (NH4+) substituting for K+ in some K-bearing minerals such as clays, micas, and feldspars, can be transferred to the deep Earth through subduction. The fate of ammonium in those minerals during subduction is still poorly known but is likely controlled by temperature and pressure pathways. In an attempt to contribute to understanding the fate of N during high-temperature processes, we carried out in situ high-temperature IR and Raman spectra measurements to investigate the rate and mechanism of NH4+ loss in phengite. We observed that a new OH band at 3425 cm−1 became prominent above 400 °C, and did not change with times during isothermal annealing at 500 and 700 °C. The N-H stretching band shifted to higher wavenumbers in the temperature interval from −150 to 20 °C, while linearly shifted to lower wavenumbers in the temperature interval from 20 to 500 °C and remained stable above 500 °C. The N-H bending band linearly shifted to lower wavenumbers in the temperature interval from −150 to 400 °C and remained stable. The K-O stretching frequency decreased with increasing temperature to 600 °C, and then remained stable. These processes were reversible until dehydration and ammonium loss from phengite starting at 800 °C. The results suggest that (1) at low temperatures, ammonium is ordered and hydrogen bonding between ammonium and the framework evolves during cooling; (2) at high temperatures, the N-H interatomic distance of NH4+ lengthens with increasing temperature until 500 °C. N-H bond subsequently no longer lengthens, accompanied by H transferring from N to neighboring O and forming a new OH band at 3425 cm−1. At 800 °C, H+ starts breaking from N and leaving others to form NH3 and OH−. This study has implications for evaluating the extent to which these minerals can preserve information regarding nitrogen behavior during high-temperature processes.

Synchrotron FTIR imaging of OH in quartz mylonites

Abstract. Previous measurements of water in deformed quartzites using conventional Fourier transform infrared spectroscopy (FTIR) instruments have shown that water contents of larger grains vary from one grain to another. However, the non-equilibrium variations in water content between neighboring grains and within quartz grains cannot be interrogated further without greater measurement resolution, nor can water contents be measured in finely recrystallized grains without including absorption bands due to fluid inclusions, films, and secondary minerals at grain boundaries.Synchrotron infrared (IR) radiation coupled to a FTIR spectrometer has allowed us to distinguish and measure OH bands due to fluid inclusions, hydrogen point defects, and secondary hydrous mineral inclusions through an aperture of 10 µm for specimens > 40 µm thick. Doubly polished infrared (IR) plates can be prepared with thicknesses down to 4–8 µm, but measurement of small OH bands is currently limited by strong interference fringes for samples < 25 µm thick, precluding measurements of water within individual, finely recrystallized grains. By translating specimens under the 10 µm IR beam by steps of 10 to 50 µm, using a software-controlled x − y stage, spectra have been collected over specimen areas of nearly 4.5 mm2. This technique allowed us to separate and quantify broad OH bands due to fluid inclusions in quartz and OH bands due to micas and map their distributions in quartzites from the Moine Thrust (Scotland) and Main Central Thrust (Himalayas).Mylonitic quartzites deformed under greenschist facies conditions in the footwall to the Moine Thrust (MT) exhibit a large and variable 3400 cm−1 OH absorption band due to molecular water, and maps of water content corresponding to fluid inclusions show that inclusion densities correlate with deformation and recrystallization microstructures. Quartz grains of mylonitic orthogneisses and paragneisses deformed under amphibolite conditions in the hanging wall to the Main Central Thrust (MCT) exhibit smaller broad OH bands, and spectra are dominated by sharp bands at 3595 to 3379 cm−1 due to hydrogen point defects that appear to have uniform, equilibrium concentrations in the driest samples. The broad OH band at 3400 cm−1 in these rocks is much less common. The variable water concentrations of MT quartzites and lack of detectable water in highly sheared MCT mylonites challenge our understanding of quartz rheology. However, where water absorption bands can be detected and compared with deformation microstructures, OH concentration maps provide information on the histories of deformation and recovery, evidence for the introduction and loss of fluid inclusions, and water weakening processes.

Spectral properties of weathered and fresh rock surfaces in the Xiemisitai metallogenic belt, NW Xinjiang, China

AbstractSurfaces weathering of rocks in which mineral materials may be similar to or quite different from the minerals in the underlying parent rock completely control the reflectance spectra of the terrain. Our study of typical weathered and fresh rock samples from the Xiemisitai metallogenic belt, Western Junggar region, Xinjiang, found that weathering results in the formation of new materials that cause differences in the spectral features of fresh and weathered rock surfaces. Alterations induce variations in spectrum brightness, presence and intensity of characteristic absorption features, and spectral slope. Spectral differences between weathered and fresh rock surfaces are small for rhyolite, granite, and tuffaceous sandstone, but large for andesite, basalt, and diorite. Spectral changes in the 350–1000 nm wavelength region are attributed to alteration of iron oxides by atmospheric processes or secondary alteration of iron-rich minerals. Spectral features between 1000–2500 nm are caused by O–H vibrations, with features at 2200–2500 nm solely attributed to hydroxyl groups. The strongest Al–OH bands appear near 2200 nm, while Mg–OH bands are found near 2300 nm and 2350 nm. Results from this study can be used to better characterize and discriminate lithological units and potential mineral zones using hyperspectral and multispectral remote sensing techniques.

Characterization of a microwave-excited atmospheric-pressure argon plasma jet using two-parallel-wires transmission line resonator

This paper presents a method to produce a microwave-excited atmospheric-pressure plasma jet (ME-APPJ) with argon. The plasma was generated by a microwave-driven micro-plasma source that uses a two-parallel-wire transmission line resonator (TPWR) operating at around 900 MHz. The TPWR has a simple structure and is easier to fabricate than coaxial transmission line resonator (CTLR) devices. In particular, the TPWR can sustain more stable ME-APPJ than the CTLR can because the gap between the electrodes is narrower than that in the CTLR. In experiments performed with an Ar flow rate from 0.5 to 8.0 L·min−1 and an input power from 1 to 6 W, the rotational temperature was determined by comparing the measured and simulated spectra of rotational lines of the OH band and the electron excitation temperature determined by the Boltzmann plot method. The rotational temperature obtained from OH(A-X) spectra was 700 K to 800 K, whereas the apparent gas temperature of the plasma jet remains lower than ∼325 K, which is compatible with biomedical applications. The electron number density was determined using the method based on the Stark broadening of the hydrogen Hβ line, and the measured electron density ranged from 6.5 × 1014 to 7.6 × 1014 cm−3. TPWR ME-APPJ can be operated at low flows of the working gas and at low power and is very stable and effective for interactions of the plasma with cells.

Salt Promotes Protonation of Amine Groups at Air/Water Interface.

Interfacial water reorientation caused by charged Langmuir monolayers consisting of primary fatty amine (ODA) and cationic lipid having quaternary amine headgroup (DPTAP) were investigated by interface-selective vibrational sum-frequency generation spectroscopy. For DPTAP monolayer, initially large sum-frequency intensity from interfacial water OH band decreased steadily by increasing monovalent salt (NaCl, NaI) concentration due to counterion adsorption. On the other hand, ODA/water exhibited significantly smaller sum-frequency intensity than DPTAP/water, implying only small portion of protonated amine group (-NH3+) initially existed. By increasing the ionic strength, however, SF intensity of water OH band was enhanced markedly up to ∼1 mM, and then decreased in both NaCl and NaI solutions. By measuring the phase of the sum-frequency spectra, it was found that water dipoles under the ODA headgroup point downward, indicating that the surfaces were always positively charged. This demonstrated that increasing ionic strength facilitates protonation of primary amine headgroups. A simple model based on Poisson-Boltzmann (PB) theory explained this protonation behavior of primary amines.

Water retained in tall Cryptomeria japonica leaves as studied by infrared micro-spectroscopy.

Recent studies in the tallest tree species suggest that physiological and anatomical traits of tree-top leaves are adapted to water-limited conditions. In order to examine water retention mechanism of leaves in a tall tree, infrared (IR) micro-spectroscopy was conducted on mature leaf cross-sections of tall Cryptomeria japonica D. Don from four different heights (51, 43, 31 and 19 m). We measured IR transmission spectra and mainly analyzed OH (3700-3000 cm-1) and C-O (1190-845 cm-1) absorption bands, indicating water molecules and sugar groups, respectively. The changes in IR spectra of leaf sections from different heights were compared with bulk-leaf hydraulics. Both average OH band area of the leaf sections and leaf water content were larger in the upper-crown, while osmotic potential at saturation did not vary with height, suggesting higher dissolved sugar contents of upper-crown leaves. As cell-wall is the main cellular structure of leaves, we inferred that larger average C-O band area of upper-crown leaves reflected higher content of structural polysaccharides such as cellulose, hemicellulose and pectin. Infrared micro-spectroscopic imaging showed that the OH and C-O band areas are large in the vascular bundle, transfusion tissue and epidermis. Infrared spectra of individual tissue showed that much more water is retained in vascular bundle and transfusion tissue than mesophyll. These results demonstrate that IR micro-spectroscopy is a powerful tool for visualizing detailed, quantitative information on the spatial distribution of chemical substances within plant tissues, which cannot be done using conventional methods like histochemical staining. The OH band could be well reproduced by four Gaussian OH components around 3530 (free water: long H bond), 3410 (pectin-like OH species), 3310 (cellulose-like OH species) and 3210 (bound water: short H bond) cm-1, and all of these OH components were higher in the upper crown while their relative proportions did not vary with height. Based on the spectral analyses, we inferred that polysaccharides play a key role in biomolecular retention of water in leaves of tall C. japonica.

Lidar sensing of ship wakes

Detection of ship wakes is utterly important for ship traffic monitoring, security of sea borders, etc. Among standard detection methods there are radar and acoustic sensing, photographing, hyperspectral measurements, and water sample analysis. However, these methods are hardly suitable for detecting wakes of light high-speed boats. An alternative is optical methods, in particular laser remote sensing. In this work, laboratory experiments on laser remote sensing of water perturbed by a propeller rotating at up to 20 000 rpm are described. A long (over 5 h) decrease in the integral of the band of OH stretching vibrations inH2Omolecules in the Raman scattering spectrum and a blueshift of theOHband center by 2.5 to 3 cm−1 are demonstrated.

CO2 Hydration Shell Structure and Transformation.

The hydration-shell of CO2 is characterized using Raman multivariate curve resolution (Raman-MCR) spectroscopy combined with ab initio molecular dynamics (AIMD) vibrational density of states simulations, to validate our assignment of the experimentally observed high-frequency OH band to a weak hydrogen bond between water and CO2. Our results reveal that while the hydration-shell of CO2 is highly tetrahedral, it is also occasionally disrupted by the presence of entropically stabilized defects associated with the CO2-water hydrogen bond. Moreover, we find that the hydration-shell of CO2 undergoes a temperature-dependent structural transformation to a highly disordered (less tetrahedral) structure, reminiscent of the transformation that takes place at higher temperatures around much larger oily molecules. The biological significance of the CO2 hydration shell structural transformation is suggested by the fact that it takes place near physiological temperatures.

Optical characteristics of UV–VUV lamps on the electronic‐vibrational transitions of the hydroxyl radical pumped by a nanosecond capacitive discharge

This paper presents the results of a study of UV and VUV low-pressure lamp pumped by nanosecond capacitive discharge. This lamp works on the mixtures of helium and argon with water vapor (H2O) or ‘heavy’ water (D2O). At the capacitive low-pressure lamp emission spectra are mainly narrow band 308 nm OH (A–X) and large band in the VUV spectral range: 140–200 nm OH (C, B, A). Found, that the increasing the partial pressure of H2O and D2O (>130–150 Pa) led to a decrease in the intensity of VUV radiation of hydroxyl radicals. In the transition from He/H2O mixture to He/D2O mixture, the optimal pressure of helium is decreased. Reduced partial pressure of argon led to increased intensity of radiation of hydroxyl in the VUV range. The study of emission characteristics of OD* – lamps on a mixture of He/D2O and the OH* – lamps on a mixture of He/H2O showed that the intensity of the bands OD (X, C, A) is 1.5 times larger than the intensity of the bands OH (X, C, A). The maximum absolute intensity of UV–VUV radiation of the lamp (at a frequency of 1000 Hz) reached 1 W.

15 years of VLT/UVES OH intensities and temperatures in comparison with TIMED/SABER data

The high-resolution echelle spectrograph UVES of the Very Large Telescope at Cerro Paranal in Chile has been regularly operated since April 2000. Thus, UVES archival data originally taken for astronomical projects but also including sky emission can be used to study airglow variations on a time scale longer than a solar cycle. Focusing on OH emission and observations until March 2015, we considered about 3000 high-quality spectra from two instrumental set-ups centred on 760 and 860 nm, which cover about 380 nm each. These data allowed us to measure line intensities for several OH bands in order to derive band intensities and rotational temperatures for different upper vibrational levels as a function of solar activity and observing date. The results were compared with those derived from emission and temperature profile data of the radiometer SABER on the TIMED satellite taken in the Cerro Paranal area between 2002 and 2015. In agreement with the SABER data, the long-term variations in OH intensity and temperature derived from the UVES data are dominated by the solar cycle, whereas secular trends appear to be negligible. Combining the UVES and SABER results, the solar cycle effects for the OH intensity and temperature are about 12–17% and 4–5 K per 100 sfu and do not significantly depend on the selected OH band. The data also reveal that variations of the effective OH emission layer height and air density can cause significant changes in the OH rotational temperatures due to a varying ratio of OH thermalising collisions by air molecules and OH radiation, deactivation, and destruction processes which impede the rotational relaxation. However, this effect appears to be of minor importance for the explanation of the rotational temperature variations related to the solar activity cycle, which causes only small changes in the OH emission profile.

Simultaneous Visualization of Hydrogen Peroxide and Water Concentrations Using Photofragmentation Laser-Induced Fluorescence

A concept based on photofragmentation laser-induced fluorescence (PFLIF) is for the first time demonstrated for simultaneous detection of hydrogen peroxide (H2O2) and water (H2O) vapor in various mixtures containing the two constituents in a bath of argon gas. A photolysis laser pulse at 248 nm dissociates H2O2 into OH fragments, whereupon a probe pulse, delayed 100 ns and tuned to an absorption line in the A2Σ+ (v = 1) ← X2Π(v = 0) band of OH near 282 nm, induces fluorescence. The total OH fluorescence reflects the H2O2 concentration, while its spectral shape is utilized to determine the H2O concentration via a model predicting the ratio between the fluorescence intensities of the A2Σ+ (v = 1) → X2Π(v = 1) and the A2Σ+ (v = 0) → X2Π(v = 0) bands. The H2O detection scheme requires that the bath gas has a collisional cross-section with OH(A) that is significantly lower than that of H2O, which is the case for argon. Spectrally dispersed OH fluorescence spectra were recorded for five different H2O2/H2O/Ar mixtures; the H2O2 concentration in the range of 30-500 ppm and the H2O concentration in the range of 0-3%. Fluorescence intensity ratios predicted by the model for these mixtures agree very well with corresponding experimental data, which thus validates the model. The concept was also demonstrated for two-dimensional imaging, using two intensified charge-coupled device (CCD) cameras for signal detection. Water content was here sensed through the different temporal characteristics of the two fluorescence bands by triggering the two cameras so that one captures the total OH fluorescence while the other one captures only the early part, which mainly stems from A2Σ+ (v = 1) → X2Π(v = 1) fluorescence. Hence, the H2O2 concentration is reflected by the image of the camera recording the total OH fluorescence, whereas H2O concentration is extracted from the ratio between the two camera images. Quantification of the concentrations was carried out based on calibration measurements performed in known mixtures of H2O2 (30-500 ppm) and H2O (0-3%) in bulk argon. The detection limits for single-shot imaging are estimated to be 20 ppm for H2O2 and 0.05% for H2O. The authors believe that the concept provides a valuable asset in, for example, pharmaceutical or aseptic food packaging applications, where H2O2/H2O vapor is routinely used for sterilization.

Variability of OH(3-1) and OH(6-2) emission altitude and volume emission rate from 2003 to 2011

In this study we report on variability in emission rate and centroid emission altitude of the OH(3-1) and OH(6-2) Meinel bands in the terrestrial nightglow based on spaceborne nightglow measurements with the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument on the Envisat satellite. The SCIAMACHY observations cover the time period from August 2002 to April 2012 and the nighttime observations used in this study are performed at 10:00p.m. local solar time. Characterizing variability in OH emission altitude – particularly potential long-term variations – is important for an appropriate interpretation of ground-based OH rotational temperature measurements, because simultaneous observations of the vertical OH volume emission rate profile are usually not available for these measurements. OH emission altitude and vertically integrated emission rate time series with daily resolution for the OH(3-1) band and monthly resolution for the OH(6-2) band were analyzed using a standard multilinear regression approach allowing for seasonal variations, QBO-effects (Quasi-Biennial Oscillation), solar cycle (SC) variability and a linear long-term trend. The analysis focuses on low latitudes, where SCIAMACHY nighttime observations are available all year. The dominant sources of variability for both OH emission rate and altitude are the semi-annual and annual variations, with emission rate and altitude being highly anti-correlated. There is some evidence for a 11-year solar cycle signature in the vertically integrated emission rate and in the centroid emission altitude of both the OH(3-1) and OH(6-2) bands.

Spectroscopic characterization of energy transfer and thermal conditions of the flame kernel in a spark ignition engine fueled with methane and hydrogen

In the context of stringent exhaust gas emission regulations and requirements of increased efficiency, spark ignition (SI) engine research is looking at ever more detailed approaches, that cover a large number of processes. Ignition is one of the determining factors for repeatable combustion and its study is associated with extensive difficulties due to the turbulent nature of fluid motion. In order to provide data on the energy transfer and thermal conditions of the flame kernel in its initial stages, vibrational and rotational temperatures were evaluated using UV emission spectra detected in a SI engine. Stoichiometric operation with methane and hydrogen–methane blends was employed, so as to identify any influence of the fuel's molecular structure on these processes. The consolidated methodology for temperature estimation using the ratio between the emission bands of CN and OH, was implemented considering the effects of collisional broadening. Vibrational temperatures evaluation showed and evolution from 8000 K to 4000 K during the arc and glow phase specific for SI. The evolution of CN emission intensity confirmed its formation only in the initial stages of ignition, for which kernel temperature is high enough. Simulations of chemical equilibrium showed that the evaluation of temperatures based on spectroscopic measurements is in line with the decreasing trend correlated with the electrical current evolution, measured in the secondary circuit.

Characterization of Individual Hydrogen Bonds in Crystalline Regenerated Cellulose Using Resolved Polarized FTIR Spectra.

Cellulose nanofibers (CNFs), which are directly isolated as a native form, have drawn considerable attention as eco-friendly and distinctive material to be partly substituted for fossil products. In addition to the increasing attention to the native CNFs, conventional regenerated cellulose having cellulose II crystals also attracts more attention because of its cost-effective method of production in a moderately easy and repeatable fashion. Inter- and intramolecular hydrogen bonds are, in particular, thought to contribute greatly to the physical properties of cellulosic commercial products. More than half century ago, Marchessault et al. attempted to directly assign the hydroxyl (OH) group vibrations related to hydrogen bonding in infrared (IR) spectra. The assignment, however, has not been significantly updated. One reason for the delayed assignments is the difficulty in preparing pure cellulose II. Here, we show successful IR assignments of the interacted OH groups in cellulose II by using the nematic ordered cellulose to prepare a highly oriented regenerated film. The film had anisotropic crystalline domains, which provided a clearly resolved component in the IR spectra. The OH bands were well assigned, and this IR assignment becomes an effective tool to understand the structure–property relationship for engineering advanced regenerated cellulose materials.

Infrared absorption of methanol-water clusters (CH3OH)n(H2O), n = 1-4, recorded with the VUV-ionization/IR-depletion technique.

We recorded infrared (IR) spectra in the CH- and OH-stretching regions of size-selected clusters of methanol (M) with one water molecule (W), represented as MnW, n = 1-4, in a pulsed supersonic jet using the photoionization/IR-depletion technique. Vacuum ultraviolet emission at 118 nm served as the source of ionization in a time-of-flight mass spectrometer to detect clusters MnW as protonated forms Mn-1WH+. The variations in intensities of Mn-1WH+ were monitored as the wavelength of the IR laser light was tuned across the range 2700-3800 cm-1. IR spectra of size-selected clusters were obtained on processing of the observed action spectra of the related cluster-ions according to a mechanism that takes into account the production and loss of each cluster due to IR photodissociation. Spectra of methanol-water clusters in the OH region show significant variations as the number of methanol molecules increases, whereas those in the CH region are similar for all clusters. Scaled harmonic vibrational wavenumbers and relative IR intensities predicted with the M06-2X/aug-cc-pVTZ method for the methanol-water clusters are consistent with our experimental results. For dimers, absorption bands of a structure WM with H2O as a hydrogen-bond donor were observed at 3570, 3682, and 3722 cm-1, whereas weak bands of MW with methanol as a hydrogen-bond donor were observed at 3611 and 3753 cm-1. For M2W, the free OH band of H2O was observed at 3721 cm-1, whereas a broad feature was deconvoluted to three bands near 3425, 3472, and 3536 cm-1, corresponding to the three hydrogen-bonded OH-stretching modes in a cyclic structure. For M3W, the free OH shifted to 3715 cm-1, and the hydrogen-bonded OH-stretching bands became much broader, with a weak feature near 3179 cm-1 corresponding to the symmetric OH-stretching mode of a cyclic structure. For M4W, the observed spectrum agrees unsatisfactorily with predictions for the most stable cyclic structure, indicating significant contributions from branched isomers, which is distinctly different from M5 of which the cyclic form dominates.

Abundances of the light elements from UV (HST) and red (ESO) spectra in the very old star HD 84937

Aims. In order to provide a better basis for the study of mechanisms of nucleosynthesis of the light elements beyond hydrogen and helium in the oldest stars, the abundances of C, O, Mg, Si, P, S, K, and Ca have been derived from UV-HST and visible-ESO high resolution spectra in the old, very metal-poor star HD 84937, at a metallicity that is 1/200 that of the Sun’s. For this halo main-sequence turnoff star, the abundance determination of P and S are the first published determinations. Methods. The LTE profiles of the lines were computed and fitted to the observed spectra. Wherever possible, we compared the abundances derived from the UV spectrum to abundances derived from the visible or near-infrared spectra, and also corrected the derived abundances for non-LTE effects. Three-dimensional (3D) CO5BOLD model atmospheres have been used to determine the abundances of C and O from molecular CH and OH bands. Results. The abundances of these light elements relative to iron in HD 84937 are found to agree well with the abundances of these elements in classical metal-poor stars. Our HD 84937 carbon abundance determination points toward a solar (or mildly enhanced above solar) value of [C/Fe]. The modest overabundance of the α elements of even atomic number Z, typical of halo turnoff stars, is confirmed in this example. The odd-Z element P is found to be somewhat deficient in HD 84937, at [P/Fe] = −0.32, which is again consistent with the handful of existing determinations for turnoff stars of such low metallicity. We show that the abundance of oxygen, deduced from the OH band from 3D computations, is not compatible with the abundance deduced from the red oxygen triplet. This incompatibility is explained by the existence of a chromosphere heating the shallow layers of the atmosphere where the OH band, in 3D computations, is mainly formed. Conclusions. The abundance ratios are compared to the predictions of models of galactic nucleosynthesis and evolution.

In-situ infrared spectra of OH in rutile up to 1000 °C

The infrared spectra of hydrous, oriented single crystals of synthetic Al-doped and pure rutile were measured from room temperature to 1000 °C at 1 bar using a heating stage. At room temperature, the spectra show only one band at ~3278 cm−1 in pure rutile, and two additional bands at ~3303 and 3323 cm−1 in Al-doped rutile. The main band associated with Al at ~3323 cm−1 loses intensity as temperature increases and nearly disappears already at 300 °C. This suggests that the corresponding defect only forms during cooling and, therefore, water speciation in rutile at room temperature is not representative of subduction zone or upper mantle conditions. All OH bands shift to lower wavenumbers at elevated temperatures with dν/dT = −0.0831 cm−1 K−1 for the main band at 3278 cm−1. This strong low-frequency shift is unexpected for an OH bond involved in hydrogen bonding, indicating decreasing O–O distance for the OH band. Together with the extreme broadening of the band at high temperature, it suggests some weakening of the OH bond strength and a rapid exchange of protons, consistent with rapid hydrogen diffusion in rutile.

Synergistic solvent extraction of vanadium from leaching solution of stone coal using D2EHPA and PC88A

Abstract New extractant and an extractant system are attractive for liquid-liquid extraction. To improve the extraction efficiency and selectivity, the binary extractant system consisting of bis-2-ethylhexyl phosphoric acid (D2EHPA) and 2-ethylhexylphosphonic mono-2-ethylhexyl (PC88A) was explored to separate vanadium (V) via synergism from multi-element sulphuric acid leaching solution in this study. The optimal proportion and concentration of extractant was investigated and results demonstrated that the maximum synergistic co-efficient was 1.52 by adjusting the volume ratio to 14:6 (D2EHPA/PC88A) when the extractant concentration was 20% (v/v). Next, the selectivity of the mixture was investigated at different pH values and contact time, which demonstrated better separation of vanadium from primary impurities compared with extraction by D2EHPA or PC88A alone. Furthermore, the Fourier Transform Infrared (FT-IR) spectra were employed to analyse the mechanism of extraction. The results suggested that the cation exchange (P OH bands) and coordination reaction (P O bands) contribute to vanadium extraction, and the structure of extracted complex was proposed. The formation of a dimer between D2EHPA and PC88A was demonstrated. Finally, after multi-stage counter-current extraction and stripping, V2O5 product with a high purity of 99.07% was obtained by oxidation, precipitation and calcination.

Large- and small-scale periodicities in the mesosphere as obtained from variations in O<sub>2</sub> and OH nightglow emissions

Abstract. Using 3 years (2013–2015) of O2(0–1) and OH(6–2) band nightglow emission intensities and corresponding rotational temperatures as tracers of mesospheric dynamics, we have investigated large- and small-timescale variations in the mesosphere over a low-latitude location, Gurushikhar, Mount Abu (24.6° N, 72.8° E), in India. Both O2 and OH intensities show variations similar to those of the number of sunspots and F10.7 cm radio flux with coherent periodicities of 150 ± 2.1, 195 ± 3.6, 270 ± 6.4, and 420 ± 14.8 days, indicating a strong solar influence on mesospheric dynamics. In addition, both mesospheric airglow intensities also showed periodicities of 84 ± 0.6, 95 ± 0.9, and 122 ± 1.3 days which are of atmospheric origin. With regard to the variability of the order of a few days, O2 and OH intensities were found to be correlated, in general, except when altitude-dependent atmospheric processes were operative. To understand mesospheric gravity wave behavior over the long term, we have carried out a statistical study using the periodicities derived from the nocturnal variations in all four parameters (O2 and OH intensities and their respective temperatures). It was found that the major wave periodicity of around 2 h duration is present in all the four parameters. Our analyses also reveal that the range of periods in O2 and OH intensities and temperatures is 11 to 24 and 20 to 60 min, respectively. Periods less than 15 min were not present in the temperatures but were prevalent in both emission intensities. No seasonal dependence was found in either the wave periodicities or the number of their occurrence.

Spatially resolved measurements and diagnostics of digitally controlled rotating field pulsed plasma operated in helium at 20 kHz

Using optical emission spectrometry, fundamental properties are investigated of a stable, planar atmospheric pressure micro discharge, several dozen microliters in volume, driven by a digitally controlled 20kHz rotating microsecond pulsed power. The discharge is generated by rectangular wave pulses using helium as the working gas. At a low cost, the digitally controlled plasma source produces a highly symmetrical, non-stationary helium discharge maintained in open air within 5 electrodes positioned in the plane toward the center. It has been shown that the geometrical shapes of the momentary discharges, which occur between the electrodes, are not arc-like shaped, but rather have a diffusive character and the resulting plasma can become doughnut-like in shape.Rotational and vibrational temperatures from OH and N2 bands, excitation temperatures from He lines and ionization temperatures from Ca lines, as well as electron number densities from Hβ Stark broadening have been estimated along the plasma diameter using axial viewing. The results demonstrated that Texc (He) reaches stable value of 3800K for selected plasma generation conditions (one anode and two cathodes commutation mode, cathode pulse width 8 microseconds, supplied power 200W, helium gas flow 1L·min−1), while the Trot (OH) is considerably lower (1700K). The electron number density has been evaluated to be (1.7–3.3)×1014cm−3 and both Tion (Ca) and Tvib (N2) varied, throughout in the 4500–5100K and 4000–4800K ranges respectively, reaching its peak value near 2mm off the plasma axis.Spatial measurements revealed symmetrical distribution of the plasma parameters, while the measurements of calcium and nitrogen ionic emission confirmed symmetrical doughnut shape of the discharge. Moreover, the processes running inside the discharge and their interaction with the surrounding atmosphere have been described in accordance to the recorded spectra. Spectroscopic observation has shown the existence of N2+ molecular ions, although their emission profile differs significantly from neutral N2. Namely, the population of ionic molecules forms a doughnut shape, while the N2 population exhibits disk shape, indicating that plasma ionization zone is located off-axis.