Hydroxyl Absorption Research Articles

Reactive Aging of Films of Secondary Organic Material Studied by Infrared Spectroscopy

The reactive aging of films of secondary organic material (SOM) to ozone, irradiation, and water was studied by attenuated total reflectance infrared spectroscopy (ATR-IR). The films were prepared by deposition onto the ATR elements of particles produced by reaction of isoprene with hydroxyl radicals and of α-pinene with ozone in the Harvard Environmental Chamber (HEC). The infrared spectra showed that the isoprene-derived film had strong hydroxyl absorptions whereas the α-pinene-derived film had strong carbonyl absorptions. The organic films were exposed to dry and humid flows of ozone, as well as to ultraviolet irradiation, to mimic reactive aging processes that can occur in the troposphere. Both the isoprene- and α-pinene-derived films were nonreactive with respect to ozone exposure, for both dry and humid conditions, indicating that the secondary organic material consisted mostly of saturated organic species. Both films, however, were susceptible to aging by ultraviolet radiation possibly due to the presence of organic hydroperoxides, and all functional groups other than carbonyls decreased upon irradiation. In regard to hygroscopicity, as a benchmark the ratio x(W_CO) for oxalic acid of the intensity of the water-bending peak to that of carbonyl absorption (arising from carboxylic acids) was recorded from 20% to 80% relative humidity (RH). This quantity was then also measured for the isoprene- and α-pinene-derived organic films. The result of (x(W_CO))(isoprene) > (x(W_CO))(benchmark) across the range of studied RH values shows that species other than carboxylic acids contributed significantly to the hygroscopicity of the isoprene-derived film. The spectra were consistent with alcohols and hydroperoxides as the hygroscopic components. By comparison, the result of (x(W_CO))(pinene) ≈ (x(W_CO))(benchmark) indicates a dominance of carboxylic acids with respect to the hygroscopicity of this film.

EFFECT OF THERMAL TREATMENT WITH METHYLOLUREA IMPREGNATED ON POPLAR WOOD

The aim of this research was to study the physical and chemical performance of poplar wood treated by chemi-thermal modification. A thermal treatment was used to catalyze the effect of the methylolurea impregnated pre-treatment by curing the poplar wood at 160 °C under atmospheric conditions. The results showed that the thermal treatment played an important role in the chemical and mechanical performance. Such an approach not only can significantly reduce the hygroscopicity, but also can increase the bending strength and compressive strength parallel to grain. The positions of the XRD peaks did not change, which indicated that the structure of cellulose was not noticeably affected by the thermal treatment. The FT-IR analysis showed that the intensity of hydroxyl and carbonyl absorption peaks decreased significantly, which indicated that the NH-CH2-OH of methylolurea reacted with the wood carboxyl (C=O) and hydroxyl (-OH). The TGA showed that the thermal stability of treated wood improved. The SEM showed that the cell wall and vessels were filled with impregnated chemicals.

The C-O Stretching Infrared Band as a Probe of Hydrogen Bonding in Ethanol–Water and Methanol–Water Mixtures

ABSTRACT Infrared spectra of the ethanol–water and methanol–water mixtures in the mole fraction range of 0.1 to 0.9 were recorded in the attenuated reflection (ATR) mode. Traditionally, the hydrogen bonding of water with other molecules has been studied by investigation of the OH stretching band frequencies and intensities of water. However, in the case of alcohol–water mixtures, this procedure presents a problem due to the complete overlap of the hydroxyl absorptions from the alcohol and water. In the present study, we have adopted an alternative approach of understanding the ethanol–water and methanol–water hydrogen bonds through the analysis of the C-O stretching band. The intrinsic high intensity of the C-O band and nearly complete absence of its overlap with the water bands make it a good candidate for the study of hydrogen bonding interactions in alcohol–water mixtures. The integrated areas of the C-O stretching band versus mole fractions were plotted for both mixtures. In the case of methanol–water mixtures, the C-O stretching band area plot was linear, whereas such plot for the ethanol–water mixtures had two distinct slopes that switched at the 0.5 mole fraction. The C-O band plot areas were used to explain the molecular associations in the mixtures studied.

Reversible Superhydrophobic–Superhydrophilic Transition of ZnO Nanorod/Epoxy Composite Films

Tuning the surface wettability is of great interest for both scientific research and practical applications. We demonstrated reversible transition between superhydrophobicity and superhydrophilicity on a ZnO nanorod/epoxy composite film. The epoxy resin serves as an adhesion and stress relief layer. The ZnO nanorods were exposed after oxygen reactive ion etching of the epoxy matrix. A subsequent chemcial treatment with fluoroalkyl and alkyl silanes resulted in a superhydrophobic surface with a water contact angle up to 158.4° and a hysteresis as low as 1.3°. Under UV irradiation, the water contact angle decreased gradually, and the surface eventually became superhydrophilic because of UV induced decomposition of alkyl silanes and hydroxyl absorption on ZnO surfaces. A reversible transition of surface wettability was realized by alternation of UV illumination and surface treatment. Such ZnO nanocomposite surface also showed improved mechanical robustness.

Yb3+ doped fluorophosphate laser glasses with high gain coefficient and improved laser property

Yb3+ doped fluorophosphate glasses with high stimulated emission cross-section, large gain coefficient and low hydroxyl absorption coefficient were prepared by high temperature melting for fiber laser applications, and their spectral, general laser parameters were investigated accordingly by means of fluorescence emission spectrum, decay cure and infrared absorption spectra. Compared with previously reported fluorophosphate glasses, the investigated fluorophosphate glasses have highest grain coefficient and maintain a maximum laser systematical factor over other various types of laser glasses. The introduction of fluorides to fluorophosphate glasses results in the low level of hydroxyl absorption coefficient and concentration. All these advantages might mean that Yb3+ doped fluorophosphate glasses are a good candidate as an active laser media for short pulse, high power laser generation used for next generation nuclear fusion.

Research of Low Rank Bituminous Coal Heat Treating and Hydrogenation Upgrading

This paper developments the research of improving the plasticity of low rank bituminous coal. The purpose is to improve the caking property of low rank bituminous coal and expand coking coal resources. The hydrothermal treatment, co-pyrolysis adding waste plastic and hydrogenation processing are chosen to process low rank bituminous coal. Several means including FTIR spectroscopy, thermogravimetric analysis, gas chromatographic(GC) and caking index are used to analyze the treated coal and generated gas products. The results show that the carboxyl groups of coal are removed after hydrothermal treatment, and the intensity of hydroxyl absorption increases. The oxygen-containing functional groups except hydroxyl groups of coal are removed after hydrogenation. The hydrogenation has obvious effects on the changes of coal structure. The reactivity and caking property of hydrotreated coal increases significantly, the indexes of coke quality of hydrotreated coal is measured to reach 16. The co-pyrolysis hydrogenation of plastic and coal results show that coal can prevent the thermal decomposition products of plastics from escaping. The caking index of hydrotreated coal with plastic is much same as that of hydrotreated coal. The addition of plastic in hydrogenation processing can not directly improve the coal plasticity.

M3 spectral analysis of lunar swirls and the link between optical maturation and surface hydroxyl formation at magnetic anomalies

We examined the lunar swirls using data from the Moon Mineralogy Mapper (M3). The improved spectral and spatial resolution of M3 over previous spectral imaging data facilitates distinction of subtle spectral differences, and provides new information about the nature of these enigmatic features. We characterized spectral features of the swirls, interswirl regions (dark lanes), and surrounding terrain for each of three focus regions: Reiner Gamma, Gerasimovich, and Mare Ingenii. We used Principle Component Analysis to identify spectrally distinct surfaces at each focus region, and characterize the spectral features that distinguish them. We compared spectra from small, recent impact craters with the mature soils into which they penetrated to examine differences in maturation trends on‐ and off‐swirl. Fresh, on‐swirl crater spectra are higher albedo, exhibit a wider range in albedos and have well‐preserved mafic absorption features compared with fresh off‐swirl craters. Albedoand mafic absorptions are still evident in undisturbed, on‐swirl surface soils, suggesting the maturation process is retarded. The spectral continuum is more concave compared with off‐swirl spectra; a result of the limited spectral reddening being mostly constrained to wavelengths less than ∼1500 nm. Off‐swirl spectra show very little reddening or change in continuum shape across the entire M3 spectral range. Off‐swirl spectra are dark, have attenuated absorption features, and the narrow range in off‐swirl albedos suggests off‐swirl regions mature rapidly. Spectral parameter maps depicting the relative OH surface abundance for each of our three swirl focus regions were created using the depth of the hydroxyl absorption feature at 2.82 μm. For each of the studied regions, the 2.82 μm absorption feature is significantly weaker on‐swirl than off‐swirl, indicating the swirls are depleted in OH relative to their surroundings. The spectral characteristics of the swirls and adjacent terrains from all three focus regions support the hypothesis that the magnetic anomalies deflect solar wind ions away from the swirls and onto off‐swirl surfaces. Nanophase iron (npFe0) is largely responsible for the spectral characteristics we attribute to space weathering and maturation, and is created by vaporization/deposition by micrometeorite impacts and sputtering/reduction by solar wind ions. On the swirls, the decreased proton flux slows the spectral effects of space weathering (relative to nonswirl regions) by limiting the npFe0 production mechanism almost exclusively to micrometeoroid impact vaporization/deposition. Immediately adjacent to the swirls, maturation is accelerated by the increased flux of protons deflected from the swirls.

Thermal removal from near-infrared imaging spectroscopy data of the Moon

[1] In the near-infrared from about 2 μm to beyond 3 μm, the light from the Moon is a combination of reflected sunlight and emitted thermal emission. There are multiple complexities in separating the two signals, including knowledge of the local solar incidence angle due to topography, phase angle dependencies, emissivity, and instrument calibration. Thermal emission adds to apparent reflectance, and because the emission's contribution increases over the reflected sunlight with increasing wavelength, absorption bands in the lunar reflectance spectra can be modified. In particular, the shape of the 2 μm pyroxene band can be distorted by thermal emission, changing spectrally determined pyroxene composition and abundance. Because of the thermal emission contribution, water and hydroxyl absorptions are reduced in strength, lowering apparent abundances. It is important to quantify and remove the thermal emission for these reasons. We developed a method for deriving the temperature and emissivity from spectra of the lunar surface and removing the thermal emission in the near infrared. The method is fast enough that it can be applied to imaging spectroscopy data on the Moon.

Solar wind contribution to surficial lunar water: Laboratory investigations

Remote infrared spectroscopic measurements have recently re-opened the possibility that water is present on the surface of the Moon. Analyses of infrared absorption spectra obtained by three independent space instruments have identified water and hydroxyl (–OH) absorption bands at ∼3 μm within the lunar surface. These reports are surprising since there are many mechanisms that can remove water but no clear mechanism for replenishment. One hypothesis, based on the spatial distribution of the –OH signal, is that water is formed by the interaction of the solar wind with silicates and other oxides in the lunar basalt. To test this hypothesis, we have performed a series of laboratory simulations that examine the effect of proton irradiation on two minerals: anorthite and ilmenite. Bi-directional infrared reflection absorption spectra do not show any discernable enhancement of infrared absorption in the 3 μm spectral region following 1 or 100 keV proton irradiation at fluences between 10 16 and 10 18 ions cm −2. In fact, the post-irradiation spectra are characterized by a decrease in the residual O–H band within both minerals. Similarly, secondary ion mass spectrometry shows a decrease rather than an increase of the water group ions following proton bombardment of ilmenite. The absence of significant formation of either –OH or H 2O is ascribed to the preferential depletion of oxygen by sputtering during proton irradiation, which is confirmed by post-irradiation surface analysis using X-ray photoelectron spectroscopy measurements. Our results provide no evidence to support the formation of H 2O in the lunar regolith via implantation of solar wind protons as a mechanism responsible for the significant O–H absorption in recent spacecraft data. We determine an upper limit for the production of surficial –OH on the lunar surface by solar wind irradiation to be 0.5% (absorption depth).

Chemical and Physical Changes for Dimensionally Stability of Compressed Wood

The objective of this study was to determine the chemical and physical changes of chemical modified on poplar wood. The chemical modifier was impregnated into cell lumen space by pulse-dipping machine to improve the dimension stability and mechanical property of timber. The timbers were compressed and dried by the multilayer hot-press drying to produce the modified timber. The modified timber had better dimension stability than the natural wood when they were immerged water continuous eight-hour. Characteristics of Fourier Transform Infrared Spectroscopy (FTIR) for modified were studied by the FTIR spectrometer. The intensity of hydroxyl absorption peak in the infrared absorption spectrogram decreased significantly, and that of carbonyl decreased lightly, which due to the bond of the function groups of -NHCH2OH of urea-formaldehyde prepolymer react with the wood carboxyl (C=O) and hydroxyl(-OH). The morphologic models of chemical within wood were discovered by SEM.

Effects of soil sample pretreatments and standardised rewetting as interacted with sand classes on Vis-NIR predictions of clay and soil organic carbon

Numerous studies have examined the soil analytical potential of diffuse reflectance spectroscopy in the near infrared range, alone or combined with the visible range (Vis-NIR). Soil organic matter (SOM), soil organic carbon (SOC) and clay content are the most commonly and successfully predicted parameters, but predictions are quite variable due e.g. to the range of soil types covered by the calibrations. Especially organic matter predictions are also suggested to be influenced by for example soil moisture content and inclusion of the visible range in the calibration. Excess quartz sand is also suggested to have a negative influence. This study was undertaken to examine the effect of a selection of standardised sample pretreatment procedures, including rewetting, on predictions of clay and SOC content. A subset of 400 samples was selected from a dataset of 3000 Swedish agricultural soils to cover clay and organic matter contents without co-variation. The selected samples were analysed by NIR and Vis-NIR on air dry samples, either carefully mixed to avoid stratification of particle size classes or shaken to promote separation, resulting in predominantly larger particles being analysed. Unshaken samples were also analysed immediately after standardised additional drying at 35 °C for 12 h and stepwise volumetric rewetting up to 30%. Shaking and additional drying had small negative effects on clay predictions, while drying only had small positive effects on SOC predictions. Volumetric rewetting to 20 or 30% before scanning reduced clay prediction errors by up to 15%, RMSEP reduced from 5.4% clay to 4.5% clay, and SOC prediction errors by up to 30%, from 0.9% SOC to 0.6% SOC, indicating that standardised rewetting should be considered. The mechanisms concerned could not be specifically identified, but known bands for water, hydroxyl and clay mineral-dependent absorption near 1400, 1900 and 2200 nm were involved in the improved clay calibrations and bands near 1700, 2000, 2300 and 2350 nm in the improved SOC calibrations. The SOC predictions were most inaccurate for soils with a high sand content. For these samples the average prediction error was more than twice as high as those for less sandy samples. Rewetting eliminated this bias, largely explaining the positive effects of rewetting.

UV/VIS, FTIR spectrum and Anticandidial activity of Streptomyces strains

Two different species Streptomyces aureofaciens and S. albidoflavus were collected from Microbial Type Culture Collection Centre, Chandigarh, India. These two species were extensively studied for their in vitro anticandidial activity. The result indicated that S. aureofaciens was highly active against Candida albicans. The UV spectral analysis of the produced antifungal metabolite of S. aureofaciens and S. albidoflavus showed the absorbance peaks at 240nm. The FTIR spectral study revealed that the ethyl acetate extracts of S. aureofaciens and S. albidoflavus fermentation broth exhibited absorption from 2956 to 2360.7cm -1 and from 3310 to 2358.8cm -1 , respectively, which indicate hydroxyl groups and absorption at 1639 cm -1 indicating a double bond of non polyenic compound.

Thermoluminescence, infrared reflectivity and electron paramagnetic resonance properties of hemimorphite

Silicate mineral hemimorphite has been investigated concerning its TL, IR and EPR properties. A broad TL peak around 180 °C and a weaker and narrower peak around 360 °C were found in a sample annealed at 600 °C for 1 h and then irradiated. The deconvolution using the CGCD method revealed peaks around 132, 169, 222 and 367 °C. The reflectivity measurements showed several bands in the NIR region due to H 2O, OH and Al–OH complexes. No band was observed in the visible region. The thermal treatments were carried out from ∼110 to 940 °C and dehydration was observed, first causing a diminishing optical absorption in general and the disappearance of water and hydroxyl absorption bands. The EPR spectrum of natural hemimorphite, presented Cu 2+ signals at g = 2.4 and g = 2.1 plus E 1′ signal superposed to Fe 3+ signal around g = 2.0.

Spectral reflectance for the mineralogical evaluation of Brazilian low clay activity soils

Highly weathered tropical soils are very important in terms of agricultural production but there are only a few spectral studies that have evaluated them in detail. Measurements of electromagnetic radiation (EMR) interactions with soil samples can provide useful information regarding mineralogy, organic matter content, granulometry as well as other important soil parameters. The objective of this study was to evaluate the relationship between analytical and spectral parameters of six important classes of tropical Brazilian soils. Spectral data were obtained under laboratory conditions using an IRIS (400–2500 nm) spectroradiometer. Soil chemical analyses were conducted as performed for pedological surveys. Spectral curves provided useful pedological information. Diagnostic mineralogical features were found for “absorption bands” that are well‐defined “valleys” centred in some wavelengths of the spectral curve. The main absorption bands were centred at 450 and 850 nm and were attributed to interactions between EMR and the content of iron oxide in the soil. Water and hydroxyl absorption bands at 1450, 1950 and 2200 nm were also enhanced, and allowed a correlation with the presence of either 2 : 1 or kaolinitic mineralogy. Important pedological characteristics such as granulometry, quartz and the presence of magnetite could also be inferred. Reflectance increased as the iron content decreased and the soil's texture changed from clay to sandy. Iron forms differentially influenced the spectral data: crystalline forms were responsible for concavities in the 450 and 1100 nm spectral range and amorphous forms reduced the intensity of reflectance, but did not alter the concavities. Rich quartz soils reflected more than soils rich in iron and magnetite. The 1 : 1 mineralogy presented spectral contours that differed from the 2 : 1 mineralogy when evaluated with the bands at 1950 and 2200 nm. In conclusion, laboratory EMR analysis of soil samples collected in the field can provide a great deal of pedological information and assist traditional methods of soil evaluation.

Hydroxyl Radical Self-Recombination Reaction and Absorption Spectrum in Water Up to 350 °C

The rate constant for the self-recombination of hydroxyl radicals (*OH) in aqueous solution giving H2O2 product has been measured from 150 to 350 degrees C by direct measurement of the *OH radical transient optical absorption at 250 nm. The values of the rate constant are smaller than previously predicted by extrapolation to the 200-350 degrees C range and show virtually no change in this range. In combining these measurements with previous results, the non-Arrhenius behavior can be well described in terms of the Noyes equation kobs-1 = kact-1+ kdiff-1, using the diffusion-limited rate constant kdiff estimated from the Smoluchowski equation and an activated barrier rate kact nearly equal to the gas-phase high-pressure limiting rate constant for this reaction. The aqueous *OH radical spectrum between 230 and 320 nm is reported up to 350 degrees C. A weak band at 310 nm grows in at higher temperature, while the stronger band at 230 nm decreases. An isosbestic point appears near 305 nm. We assign the 230 nm band to hydrogen-bonded *OH radical, and the 310 nm band is assigned to "free" *OH. On the basis of the spectrum change relative to room temperature, over half of the *OH radicals are in the latter form at 350 degrees C.

Quantitative mapping of arid alluvial fan surfaces using field spectrometer and hyperspectral remote sensing

Mapping and dating of arid and semi-arid alluvial fans are of great importance in many Quaternary studies. Yet the most common mapping method of these features is based on visual, qualitative interpretation of air-photos. In this study we examine the feasibility of mapping arid alluvial surfaces by using airborne hyperspectral reflective remote sensing methodology. This technique was tested on Late Pleistocene to Holocene alluvial fan surfaces located in the hyperarid southern Arava valley, Israel. Results of spectral field measurements showed that the surface reflectance is controlled by two main surficial processes, which are used as relative age criteria: the degree of desert pavement development (gravel coverage %) controls the absorption feature depths, while the rock coating development influences significantly the overall reflectance of the surface, but its effect on the absorption feature depths is limited. We show that as the percent of the surface covered by gravels increases, the absorption feature depth of the common gravels, in this case carbonate at 2.33 μm, increases as well; whereas the absorption features depth of the fine particle in-between the gravels, decrease (hydroxyl and ferric absorption features at 2.21 μm, and 0.87 μm, respectively), as the fines are removed from the surface. Using these correlations we were able to map the surface gravel coverage (%) on the entire alluvial fan, by calculating the gravel coverage (%) in each pixel of the hyperspectral image. The prediction of gravel coverage (%) is with accuracy of ± 15% (e.g. gravel coverage of 50% can be predicted to be 35% to 65%). Using extensive accuracy assessment data, we show that the spectral based mapping maintained high accuracy degree ( R 2 = 0.57 to 0.83). The quantitative methodology developed in this study for mapping alluvial surfaces can be adapted for other surfaces and piedmonts throughout the arid regions of the world.

Water content in natural eclogite and implication for water transport into the deep upper mantle

Infrared spectroscopy and ion micro-probe measurements showed that the major constituent minerals of eclogites from the Kokchetav massif, which have been subducted to ∼180 km depths, contain significant amounts of water up to 870 ppm H 2O (by weight) in omphacite, 130 ppm H 2O in garnet and 740 ppm H 2O in rutile. Omphacite shows three hydroxyl absorption bands at 3440–3460, 3500–3530 and 3600–3625 cm − 1 , garnet has a single band at 3580–3630 cm − 1 and rutile has a single sharp band at 3280 cm − 1 . The hydroxyl absorbance at these wavenumbers changes with the crystal orientation in polarized infrared radiation, indicating that the water is structurally incorporated in these minerals. The water contents in omphacite and garnet increase systematically with the metamorphic pressure of the host eclogites. The partitioning coefficient of the water content between coexisting garnet and omphacite is similar in different eclogites, D Grt/Omp∼0.1–0.2, but decreases slightly at high pressure. Based on the mineral proportions of the eclogites, we estimate bulk-rock water content in the eclogites ranging from 3070 to 300 ppm H 2O (by weight). Although hydrous minerals are absent in the diamond-grade eclogite (∼60 kbar and ∼1000 °C), trace amounts of water are incorporated in the nominally anhydrous minerals such as omphacite and garnet. The presence of significant water in these minerals implies that the subducting oceanic crust can transport considerable amounts of water into the deep upper mantle beyond the stability of hydrous minerals. Such water may be stored in the deep upper mantle and have an important influence on dynamics in the Earth's interior.

FTIR Spectrum of Phenocryst Olivine as an Indicator of Silica Saturation in Magmas

Fourier Transform infrared (FTIR) absorption spectra of hydroxyl were measured on olivine phenocrysts from hydrous basaltic melts that originated in island-arc tectonic settings. The basaltic melts encompass a wide range of silica activities from orthopyroxene-saturated hypersthene-normative to nepheline-normative compositions. The intensities and wavenumber placement of hydroxyl absorption bands correlate with the degree of silica saturation of the parent melt from which the olivine crystallized. Olivines from silica-undersaturated nepheline-normative melts absorb IR radiation in the wavenumber range 3430–3590 cm−1 (Group 1). In contrast, olivines from orthopyroxene-saturated boninitic melts exhibit hydroxyl absorption bands in the wavenumber range 3285–3380 cm−1 (Group 2). Olivines crystallized at intermediate silica activities exhibit a combination of the two groups of hydroxyl IR bands, where the proportion of Group 2 bands increases with increasing silica saturation of the parent melt. The positions of hydroxyl absorption peaks observed here for natural samples are consistent with previous measurements on experimentally annealed olivines. Thus protonation experiments can be employed to make spectroscopically dry olivine structures visible by IR, yielding information on the silica saturation of the parental magmas. Hydroxyl concentrations in the studied olivines were estimated to be 1–2 ppm, corresponding to an olivine–melt partition coefficient of ∼(1·0 ± 0·3) × 10−4.

VLBI imaging of OH absorption: the puzzle of the nuclear region of NGC 3079

Broad hydroxyl (OH) absorption lines in the 1667- and 1665-MHz transitions towards the central region of NGC 3079 have been observed at high resolution with the European VLBI Network (EVN). Velocity fields of two OH absorption components have been resolved across the unresolved nuclear radio continuum source of extention similar to10 pc. The velocity field of the OH absorption close to the systemic velocity shows rotation in nearly the same sense as that of the edge-on galactic-scale molecular disc probed by CO(1-0) emission. The velocity field of the blueshifted OH absorption displays a gradient in almost the opposite direction. The blueshifted velocity field represents a non-rotational component, which may trace an outflow from the nucleus, or material driven and shocked by the kiloparsec-scale superbubble. This OH absorption component traces a structure that does not support a counter-rotating disc suggested on the basis of the neutral hydrogen absorption.

A high-resolution radio study of neutral gas in the starburst galaxy NGC 520

We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ∼10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (HI) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H i absorption (N H ∼ 10 2 2 atoms cm - 2 ) traces a velocity gradient of 0.5 km s - 1 pc - 1 across the central kpc of NGC 520. The HI absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here.