Spectrum Of Mercury Research Articles

Cosmic pears from the Havelland (Germany): Ribbeck, the twelfth recorded aubrite fall in history

AbstractIn 1889 the German poet and novelist Theodor Fontane wrote the popular literary ballad “Herr von Ribbeck auf Ribbeck im Havelland.” The Squire von Ribbeck is described as a gentle and generous person, who often gives away pears from his pear trees to children passing by and continued donating pears after his death. Now, 135 years later the rock called Ribbeck is giving us insight into processes that happened 4.5 billion years ago. The meteorite Ribbeck (official find location: 52°37′15″N, 12°45′40″E) fell January 21, 2024, and has been classified as a brecciated aubrite. This meteoroid actually entered the Earth's atmosphere at 00:32:38 UTC over Brandenburg, west of Berlin, and the corresponding fireball was recorded by professional all sky and video cameras. More than 200 pieces (two proved by radionuclide analysis to belong to this fresh fall) were recovered totaling about 1.8 kg. Long‐lived radionuclide and noble gas data are consistent with long cosmic ray exposure (55–62 Ma) and a preatmospheric radius of Ribbeck between 20 and 30 cm. The heavily brecciated aubrite consists of major (76 ± 3 vol%) coarse‐grained FeO‐free enstatite (En99.1Fs<0.04Wo0.9), with a significant abundance (15.0 ± 2.5 vol%) of albitic plagioclase (Ab95.3 An2.0Or2.7), minor forsterite (5.5 ± 1.5 vol%; Fo99.9) and 3.5 ± 1.0 vol% of opaque phases (mainly sulfides and metals) with traces of nearly FeO‐free diopside (En53.2Wo46.8) and K‐feldspar (Ab4.6Or95.4). The rock has a shock degree of S3 (U‐S3), and terrestrial weathering has affected metals and sulfides, resulting in the brownish appearance of rock pieces and the partial destruction of certain sulfides already within days after the fall. The bulk chemical data confirm the feldspar‐bearing aubritic composition. Ribbeck is closely related to the aubrite Bishopville. Ribbeck does not contain solar wind implanted gases and is a fragmental breccia. Concerning the Ti‐ and O‐isotope compositions, the data are similar to those of other aubrites. They are also similar to E chondrites and fall close to the data point for the bulk silicate Earth (BSE). Before the Ribbeck meteoroid entered Earth's atmosphere, it was observed in space as asteroid 2024 BX1. The aphelion distance of 2024 BX1's orbit lies in the innermost region of the asteroid belt, which is populated by the Hungaria family of minor planets characterized by their E/X‐type taxonomy and considered as the likely source of aubrites. The spectral comparison of an average large‐scale emission spectrum of Mercury converted into reflectance and of the Ribbeck meteorite spectrum does not show any meaningful similarities.

Low sulfide concentration in Mercury’s smooth plains inhibits hollows

MESSENGER (Mercury, Surface, Space Environment, Geochemistry, and Ranging) mission to Mercury led to the discovery of hollows. These geological landforms have no close counterpart on other airless silicate bodies. Multispectral images and geochemical measurements by MESSENGER suggest that hollows are formed by the loss of volatile-bearing minerals. We investigated the mineralogical composition of the hollows using near-ultraviolet to near-infrared spectra obtained by MESSENGER. We compared reflectance spectra of hollows with laboratory spectra of Mercury's analogs: sulfides, chlorides, silicates, and graphite. The best candidates to reproduce the curvature of the hollow spectra are calcium sulfide, magnesium sulfide, and sodium sulfide. In addition, we performed spectral modeling with spectra obtained at the highest spectral and spatial resolution within the hollows. Our results show that the enrichment of sulfides in hollow material is up to two times higher than the sulfide concentration derived from chemical measurements of Mercury's high-reflectance smooth plains. This result explains the small percentage of hollows found within these plains.

Influence of unburned carbon on mercury chemical forms in fly ash produced from a coal-fired power plant

The chemical forms of mercury in coal-fired power plant fly ash were determined qualitatively and quantitatively using X-ray absorption near edge structure (XANES) analysis. Mercury content in the fly ash increased linearly with an increase in the content of unburned carbon. The inflection point method, using the first and second derivatives of XANES spectra, was used to estimate the type and abundance of chemical forms present. The XANES spectrum of fly ash mercury was modeled by a linear combination fitting of control mercury compounds, with their abundance ratios used as fitting parameters. The inflection point difference in energy was used as the requirements for simulation. The fly ash sample contained 2.6 ppm of mercury which combined with sulfur, chlorine and oxygen. The determined abundance ratios of C-Hg-S, C-Hg-Cl and C-Hg-O were 18, 27 and 36%, respectively. The unburned carbon in the fly ash was impregnated with sulfur and exposed to gaseous mercury oxide. The amount of captured mercury increased dramatically with the increase in sulfur content while chlorine and oxygen in the unburned carbon also influenced on the mercury chemical forms.

Mid‐infrared reflectance spectroscopy of aubrite components

AbstractAubrites Peña Blanca Spring and Norton County were studied in the mid‐infrared reflectance as part of a database for the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument on the ESA/JAXA BepiColombo mission to Mercury. Spectra of bulk powder size fractions from Peña Blanca Spring show enstatite Reststrahlen bands (RB) at 9 µm, 9.3 µm, 9.9 µm, 10.4 µm, and 11.6 µm. The transparency feature (TF) is at 12.7 µm, the Christiansen feature (CF) at 8.1–8.4 µm. Micro‐FTIR of spots with enstatite composition in Norton County and Peña Blanca Spring shows four types: Types I and II are similar to the bulk powder spectra but vary in band shape and probably display axis orientation. Type III has characteristic strong RB at 9.2 µm, 10.4 µm, and 10.5 µm, and at 11.3 µm. Type IV is characterized by a strong RB at 10.8−11.1 µm. Types III and IV could show signs of incipient shock metamorphism. Bulk results of this study confirm earlier spectral studies of aubrites that indicate a high degree of homogeneity and probably make the results of this study representative for spectral studies of an aubrite parent body. Spectral types I and II occur in all mineralogical settings (mineral clasts, matrix, melt, fragments in melt vein), while spectral type III was only observed among the clasts, and type IV in the melt. Comparison with surface spectra of Mercury does not obtain a suitable fit, only type IV spectra from quenched impact glass show similarity, in particular the 11 µm feature. Results of this study will be available upon request or via the IRIS database (Münster) and the Berlin Emissivity Database (BED).

Revised analysis of the third spectrum of mercury: Hg III

The doubly charged mercury (Hg III) is having the closed sub-shell 5d10(1S0) as its ground state and the first exited configuration(s) of the type 5d9nl (n ≥ 5). The spectrum of mercury was recorded on a 3-m normal incidence vacuum spectrograph at the spectroscopy laboratory of St. F. X. University in Canada. The excitation source used was a triggered spark in the wavelength region of 300–2000 Å. The theoretical calculations (inclusive of extended configurations) for the ion were accomplished by means of Cowan's quasi-relativistic Hartree-Fock code with superposition of configurations for appropriate interpretation of energy levels. Least squares fitted parametric calculations were used to elucidate the observed level structure. The obtained energy level values were optimized using a level optimization program (LOPT). A gross set of energy eigenvalues along with their LS-compositions, wavelengths and weighted transition probabilities of Hg2+ in the wavelength range 590 Å to 8200 Å are given. The ionization potential of Hg III was found to be 278,200 ± 400 cm−1 (34.49 ± 0.05 eV).

Mid-infrared spectroscopy of planetary analogs: A database for planetary remote sensing

The MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission will provide mid-infrared data, which will be crucial to characterize the surface mineralogy of Mercury. In order to interpret the results, we are creating a database of mid-infrared spectra. As part of a study of synthetic glasses which are to serve as analog materials for the interpretation of remote sensing and modeling data, we present mid-infrared data for analog materials of Mercury regolith, surface and mantle compositions. In addition, we provide data for similar analogs of Earth, Moon, Venus, and Mars rocks for a coherent picture.The analog samples have been first characterized by optical microscopy, Raman spectroscopy and EMPA. Powdered size fractions (0–25 μm, 25–63 μm, 63–125 μm, and 125–250 μm) were studied in reflectance in the mid-infrared range from 2.5 to 18 μm (550 to 2000 cm−1), additional micro-FTIR analyses were also obtained.Results for the size fractions of the surface and regolith analogs for Mercury show typical features for amorphous material with Christiansen Features (CF) at 8–8.1 μm, Reststrahlen Bands (RB) at 9.8–9.9 μm, and the Transparency Feature (TF) at 12 μm. The six bulk silicate Mercury analogs have varying CF positions from 8.1 to 9 μm, with RB crystalline features of various olivines dominating in most samples. Similarly, bulk silicate analogs of the other planetary bodies show glassy features for the surface analogs with CF from 7.9 μm (Earth Continental Crust) to 8.3 μm (Lunar Mare), strong RB from 9.5 μm (Earth Continental Crust) to 10.6 μm (Lunar Mare and Highlands). TF are usually very weak for the glassy analogs.Bulk silicate analogs for the other planetary bodies are again dominated by crystalline olivine features. Trends between SCFM (SiO2/(SiO2 + CaO + FeO + MgO)) index reflecting polymerization, CF and RB positions, and the SiO2 contents in previous studies are basically confirmed, but there is indication that several samples (Moon Mare and Highlands) do not follow the trend observed for low SiO2 samples and the RB position in earlier studies. Comparison with a ground based mid-IR spectrum of Mercury demonstrates general similarity in band positions with glassy Mercury surface and regolith material, and a chondrite based model of the planet. However, no mix so far can explain all spectral features.

Development of a High-Resolution Laser Absorption Spectroscopy Method with Application to the Determination of Absolute Concentration of Gaseous Elemental Mercury in Air.

Isotope dilution-cold-vapor-inductively coupled plasma mass spectrometry (ID-CV-ICPMS) has become the primary standard for measurement of gaseous elemental mercury (GEM) mass concentration. However, quantitative mass spectrometry is challenging for several reasons including (1) the need for isotopic spiking with a standard reference material, (2) the requirement for bias-free passive sampling protocols, (3) the need for stable mass spectrometry interface design, and (4) the time and cost involved for gas sampling, sample processing, and instrument calibration. Here, we introduce a high-resolution laser absorption spectroscopy method that eliminates the need for sample-specific calibration standards or detailed analysis of sample treatment losses. This technique involves a tunable, single-frequency laser absorption spectrometer that measures isotopically resolved spectra of elemental mercury (Hg) spectra of 6 1S0 ← 6 3P1 intercombination transition near λ = 253.7 nm. Measured spectra are accurately modeled from first-principles using the Beer-Lambert law and Voigt line profiles combined with literature values for line positions, line shape parameters, and the spontaneous emission Einstein coefficient to obtain GEM mass concentration values. We present application of this method for the measurement of the equilibrium concentration of mercury vapor near room temperature. Three closed systems are considered: two-phase mixtures of liquid Hg and its vapor and binary two-phase mixtures of Hg-air and Hg-N2 near atmospheric pressure. Within the experimental relative standard uncertainty, 0.9-1.5% congruent values of the equilibrium Hg vapor concentration are obtained for the Hg-only, Hg-air, Hg-N2 systems, in confirmation with thermodynamic predictions. We also discuss detection limits and the potential of the present technique to serve as an absolute primary standard for measurements of gas-phase mercury concentration and isotopic composition.

IR spectroscopy of synthetic glasses with Mercury surface composition: Analogs for remote sensing

In a study to provide ground-truth data for mid-infrared observations of the surface of Mercury with the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission, we have studied 17 synthetic glasses. These samples have the chemical compositions of characteristic Hermean surface areas based on MESSENGER data.The samples have been characterized using optical microscopy, EMPA and Raman spectroscopy. Mid-infrared spectra have been obtained from polished thin sections using Micro-FTIR, and of powdered size fractions of bulk material (0–25, 25–63, 93–125 and 125–250µm) in the 2.5–18µm range.The synthetic glasses display mostly spectra typical for amorphous materials with a dominating, single Reststrahlen Band (RB) at 9.5–10.7µm. RB Features of crystalline forsterite are found in some cases at 9.5–10.2µm, 10.4–11.2µm, and at 11.9µm. Dendritic crystallization starts at a MgO content higher than 23wt.% MgO.The Reststrahlen Bands, Christiansen Features (CF), and Transparency Features (TF) shift depending on the SiO2 and MgO contents. Also a shift of the Christiansen Feature of the glasses compared with the SCFM (SiO2/(SiO2+CaO+FeO+MgO)) index is observed. This shift could potentially help distinguish crystalline and amorphous material in remote sensing data. A comparison between the degree of polymerization of the glass and the width of the characteristic strong silicate feature shows a weak positive correlation.A comparison with a high-quality mid-IR spectrum of Mercury shows some moderate similarity to the results of this study, but does not explain all features.

Removal of mercury (II) from aqueous solution with three commercial raw activated carbons

In order better to comprehend the fundamental kinetics and adsorption mechanism of raw activated carbon, three typical commercial raw materials, including peach stone based activated carbon (PSAC), coal based activated carbon (CAC), and coconut husk based activated carbon (CHAC) were employed to remove mercury (II) from aqueous solutions in static batch adsorption experiments. The adsorbents were characterized by Fourier transform infrared spectrometry, X-ray diffraction analysis, surface area and porosity analysis, scanning electron microscopy, point of zero charge, isoelectric point, and X-ray photoelectron spectrometry, respectively. Four types of adsorption kinetic models and seven adsorption isotherm models were used to simulate the adsorption process. Initial solution pH, adsorbent dose, initial mercury (II) concentration, and soaking time were analyzed. The results show that theoretical maximum adsorption capacities in Langmuir monolayer model were 59.5, 48.9, and 44.9 mg/g for PSAC, CAC, and CHAC, respectively, at room temperature with initial mercury (II) concentrations of 40–450 mg/L and a pH of 4. Removal efficiencies of 94.1–99.5 % were achieved by the three absorbents. The pseudo-first-order kinetic model represented high correlations for the three adsorbents. The XPS spectra of mercury, fitting of intra-particle diffusion model and the calculation of the adsorption heat in Temkin model all indicated that the physisorption for mercury (II) was the predominant process for the three activated carbons.

Development of a 170Tm source for mercury monitoring studies in humans using XRF

The goals of the present study were to develop a 170Tm radioisotope and generate a K XRF spectrum of mercury. Thulium foil and thulium oxide powder were both tested for impurities and the latter was found to be a better prospect for further studies. The 170Tm radioisotope was developed from thulium oxide powder following the method of disolution and absorption. A suitable source holder and collimator were also designed based on Monte Carlo simulations. Using the radioisotope thus developed, a mercury XRF spectrum was successfully generated.

Space weathering of silicate regoliths with various FeO contents: New insights from laser irradiation experiments and theoretical spectral simulations

To investigate effects of micrometeorite bombardment on optical spectra and composition of planetary and asteroid regoliths with low Fe contents, we irradiated samples of a Fe-poor plagioclase feldspar (andesine–labradorite) using a nanosecond pulsed laser. We measured reflectance spectra of irradiated and non-irradiated areas of the samples (pressed pellets) between 0.5 and 18μm and performed SEM/EDS and TEM studies of the samples. Bulk FeO content of 0.72wt.% in the samples is comparable, for example, to FeO content in silicates on the surface of Mercury, that was recently mapped by NASA’s MESSENGER mission and will be spectrally mapped by remote sensing instruments MERTIS and SYMBIO-SYS on board the ESA BepiColombo spacecraft. We also employed theoretical spectral modeling to characterize optical alteration caused by formation of nano- and submicrometer Fe0 inclusions within space-weathered surface layers and grain rims of a Fe-poor regolith. The laser-irradiated surface layer of plagioclase reveals significant melting, while reflectance spectra show mild darkening and reddening in the visible and near-infrared (VNIR). Our spectral modeling indicates that the optical changes observed in the visible require reduction of bulk FeO (including Fe from mineral impurities found in the sample) and formation of nanophase (np) Fe0 within the glassy surface layer. A vapor deposit, if present, is optically too thin to contribute to optical modification of the investigated samples or to cause space weathering-induced optical alteration of Fe-poor regoliths in general. Due to low thickness of vapor deposits, npFe0 formation in the latter can cause darkening and reddening only for a regolith with rather high bulk Fe content. Our calculations show that only a fraction of bulk Fe is likely to be converted to npFe0 in nanosecond laser irradiation experiments and probably in natural regolith layers modified by space weathering. The previously reported differences in response of different minerals to laser irradiation, and probably to space weathering-induced heating are likely controlled by their differences in electrical conductivities and melting points. For a given mineral grain, its susceptibility to melting/vaporization is also affected by electric conductivities of adjacent grains of other minerals in the regolith. Published nanosecond laser irradiation experiments simulate optical alteration of immature regoliths, since only the uppermost surface layer of an irradiated pellet is subject to heating. According to our calculations, if regolith particles due to impact-induced turnover are mantled with npFe0-bearing rims of the same thickness, then even low contents of Fe similar to our sample or Mercury’ surface can cause significant darkening and reddening, provided a melt layer, rather than a thin vapor deposit is involved into npFe0 formation. All spectral effects observed in the thermal infrared (TIR) after irradiation of our feldspar sample are likely to be associated with textural changes. We expect that mineralogical interpretation of the BepiColombo MERTIS infrared spectra of Mercury between 7 and 17μm will be influenced mostly by textural effects (porosity, comminution) and impact glass formation rather than formation of npFe0 inclusions.

The low-iron, reduced surface of Mercury as seen in spectral reflectance by MESSENGER

The MESSENGER spacecraft’s Mercury Atmospheric and Surface Composition Spectrometer (MASCS) obtained more than 1.6million reflectance spectra of Mercury’s surface from near-ultraviolet to near-infrared wavelengths during the first year of orbital operations. A global analysis of spectra in the wavelength range 300–1450nm shows little regional variation in absolute reflectance or spectral slopes and a lack of mineralogically diagnostic absorptions. In particular, reflectance spectra show no clear evidence for an absorption band centered near 1μm that would be associated with the presence of ferrous iron in silicates. There is, however, evidence for an ultraviolet absorption possibly consistent with a very low iron content (2–3wt% FeO or less) in surface silicates and for the presence of small amounts of metallic iron or other opaque minerals in the form of nano- or micrometer-sized particles. These findings are consistent with MESSENGER X-ray and gamma-ray measurements of Mercury’s surface iron abundance. Although X-ray and gamma-ray observations indicate higher than expected quantities of sulfur on the surface, reflectance spectra show no absorption bands diagnostic of sulfide minerals. Whereas there is strong evidence of water ice in permanently shadowed craters near Mercury’s poles, MASCS spectra provide no evidence for hydroxylated materials near permanently shadowed craters.

The threshold photoelectron spectrum of mercury

The threshold photoelectron spectrum of mercury has been recorded over the energy range (10–40 eV) which covers the region from the lowest state of the singly charged ion, 5d106s(2S1/2), to the double charged ionic state, 5d9(2D3/2)6s(1D2). Synchrotron radiation has been used in conjunction with the penetrating-field threshold-electron technique to obtain the spectrum with high resolution. The spectrum shows many more features than observed in previous photoemission measurements with many of these assigned to satellite states converging to the double ionization limit.

Line broadening in the neutral and ionized mercury spectra

The neutral, singly, doubly and triply ionized mercury (Hg I–IV, respectively) spectral line shapes and line center positions have been investigated in the laboratory helium plasma at electron densities ranging between 9.3×1022m−3 and 1.93×1023m−3 and electron temperatures around 19,500K, both interesting for astrophysics. The mercury (natural isotope composition) atoms were sputtered from the cylindrical amalgamated gold plates located in the homogenous part of the pulsed helium discharge operating at a pressure of 665Pa in a flowing regime. The mercury spectral line profiles were recorded using the McPherson model 209 spectrograph and the Andor ICCD camera as the detection system. This research presents Stark broadening parameters, the width (W) and the shift (d), of one Hg I, 19 Hg II, 6 Hg III and 4 Hg IV lines, not investigated so far. Our experimental W values were compared with the data calculated applying various approaches. The shape and intensity of astrophysically important 398.4nm Hg II spectral line was discussed taking into account the isotope shift, hyperfine structure and Penning effects. At the mentioned plasma parameters the Stark broadening is found to be a main line broadening mechanism of the lines (λ>200nm) in the Hg I–IV spectra.

Note: Simple means for selective removal of the 365 nm line from the Hg spectrum using Dy

The emission spectrum of mercury has a notable line at about 365 nm under both low and medium-high pressure conditions. A simple filter based on a solution of dysprosium ions, Dy(3+), is shown to be very useful for applications of Hg-light sources where this line is unwanted. The presented filter is cheap, robust, and stable towards degradation or bleaching - even under intense irradiation. The absorption spectrum for the Dy-filter is presented along with emission spectra from both low-pressure and high-pressure Hg-lamps to illustrate the utility of the technique under best-case and worst-case conditions. Attenuation of the 365 nm spectral line is almost total for the low-pressure source whereas for the high-pressure source the attenuation is about a factor of three.

The optical effects of small iron particles that darken but do not redden: Evidence of intense space weathering on Mercury

Submicroscopic iron particles larger than about 50 nm, infused throughout mineral grains or glasses, are abundant in planetary materials altered by their environment such as shocked meteorites and lunar agglutinate glasses. Such particles darken their host material but do not redden their spectra but to date there has been no theoretical treatment of their optical effects. Using Mie theory, we modify the Hapke (2001) radiative transfer model of the effects of space weathering to include these effects. Comparison with laboratory measurements shows that the new treatment reproduces the relationship between submicroscopic iron size, abundance and reflectance. We apply this new model to near-IR spectra of Mercury recently obtained by the MESSENGER spacecraft and find that submicroscopic iron is much more abundant on Mercury than in lunar soils, with typical total submicroscopic iron abundances near 3.5 wt.% compared to about 0.5 wt.% for lunar soils We also find that the ratio of iron particles that darken but do not redden to the abundance of very small iron particles that impart the red slope to space weathered material is much larger than lunar (6 vs. 2). Both the total submicroscopic iron abundance and ratio of particle size fractions are consistent with the higher production of melt and vapor in micrometeorite impact on Mercury relative to the Moon ( Cintala, 1992) that enables more accumulation of space weathering products before sequestration by regolith overturn. The radiative transfer model cannot directly constrain the abundance of opaque minerals on Mercury because of ambiguities between the darkening effects of opaques and submicroscopic iron particles larger than 50 nm, but assuming the opaques are the ultimate source of the submicroscopic iron, our results place a lower limit of 4–20 wt.% on opaque abundance on Mercury depending on the composition of the opaque phase and whether titanium metal also contributes to the space weathering effect.

A comparison of the ultraviolet to near-infrared spectral properties of Mercury and the Moon as observed by MESSENGER

Measurements of the disk-integrated reflectance spectrum of Mercury and the Moon have been obtained by the MESSENGER spacecraft. A comparison of spectra from the two bodies, spanning the wavelength range 220–1450 nm, shows that the absolute reflectance of Mercury is lower than that of the nearside waxing Moon at the same phase angle with a spectral slope that is less steep at visible and near-infrared wavelengths. We interpret these results and the lack of an absorption feature at a wavelength near 1000 nm as evidence for a Mercury surface composition that is low in ferrous iron within silicates but is higher in the globally averaged abundance of spectrally neutral opaque minerals than the Moon. Similar conclusions have been reached by recent investigations based on observations from both MESSENGER and Mariner 10. There is weak evidence for a phase-reddening effect in Mercury that is slightly larger in magnitude than for the lunar nearside. An apparent absorption in the middle-ultraviolet wavelength range of the Mercury spectrum detected from the first MESSENGER flyby of Mercury is found to persist in subsequent observations from the second flyby. The current model of space weathering on the Moon, which also presumably applies to Mercury, does not provide an explanation for the presence of this ultraviolet absorption.

Effects of mercury(ii) on structural properties, electronic structure and UV absorption spectra of a duplex containing thymine–mercury(ii)–thymine nucleobase pairs

Structural properties, electronic structure and UV absorption spectra of mercury(ii) mediated metal-DNA complex, thymine-mercury(ii)-thymine base pair (T-Hg(II)-T), were theoretically and computationally investigated along with experimental data [Ono et al., J. Am. Chem. Soc., 2006, 128(7), 2172-2173]. The results were obtained by density functional theory (DFT) calculations for ground state and time-dependent DFT (TD-DFT) calculations for excited states associated with the polarized continuum model (PCM) in order to account for the bulk solvent effect. The LUMO of T-Hg(II)-T was stabilized due to the presence of Hg(II) since an unoccupied 6p orbital interacted with the 2p orbitals of thymine N3 atoms in the same way as in a pi-conjugated system. Thus, excitations in T-Hg(II)-T involve transitions qualitatively different from those of the thymine-thymine mismatch base pair (T-T). Since conventional DFT functionals lack correct description of dispersion forces, a method previously developed in our research group which combines DFT and a van der Waals correction functional was introduced to study multiple stacking nucleobase pairs. Based on the evaluated distance and the interaction energy between two stacking nucleobase pairs, the selective capturing of Hg(II) ion by T-T compared to other metal ions is explained. The calculated UV absorption spectra of multiple stacking nucleobase pairs reproduced the decrease of absorption around 260 nm and the red-shift of the main peak experimentally observed in the presence of Hg(II) ion. Detailed analysis of the electronic structure revealed that the metal-metal interaction between two Hg(II) in multiple stacking T-Hg(II)-T is the origin of the significant changes in UV absorption spectra.

A Hapke model implementation for compositional analysis of VNIR spectra of Mercury

An implementation of Hapke’s radiative transfer-based photometric model for light scattering in semi-transparent porous media is presented with special emphasis on the analysis of reflectance spectra of Mercury. The model allows intimate mixing of an arbitrary number of regolith components with varying modal abundances, modal chemistries and grain sizes, matured by microphase iron. Reflectance spectra of suites of silicates of varying grain sizes and chemistries are used to calculate the imaginary coefficient of the complex index of refraction as a function of chemistry, thus limiting the modeling effects of chemically atypical laboratory samples, and allowing controlled modeling of minerals with varying chemical compositions. The performance of the model in the visual to near-infrared wavelength range is evaluated for a range of chemically characterized silicate mixtures of terrestrial powders, meteorite powders, matured lunar return samples, and remotely sensed lunar spectra.

Spectral emissivity measurements of Mercury's surface indicate Mg- and Ca-rich mineralogy, K-spar, Na-rich plagioclase, rutile, with possible perovskite, and garnet

Mid-infrared 2-D spectroscopic measurements from 8.0 to 12.7 μm of Mercury were taken using Boston University's Mid-Infrared Spectrometer and Imager (MIRSI) mounted on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, 7–11 April 2006. Measurements reported here cover radar bright region C, a dark plains region west of Caloris Basin, and the interior of Caloris Basin. By use of spectral deconvolution with a large spectral library composed of many mineral compositions and grain size separates, we fitted, or “unmixed”, the Mercury spectra. We find mineral suites composed of magnesium-rich orthopyroxene and olivine, Ca-, Mg-, Na-rich clinopyroxene, potassium feldspar, and Na-bearing plagioclase feldspar. Both Ca- and Mg-rich garnet (pyrope and grossular, respectively) are apparently present in small amounts. Opaque minerals are required for spectral matching, with rutile (TiO 2) repeatedly providing the “best fit”. However, in the case of the radar bright region C, perovskite also contributed to a very good fit. Caloris Basin infill is rich in both potassium feldspar and Na-rich plagioclase. There is little or no olivine in the Caloris interior smooth plains. Together with the high alkali content, this indicates that resurfacing magmas were low to intermediate in SiO 2. Data suggest the dark plains exterior to Caloris are highly differentiated low-iron basaltic magmas resulting in material that might be classified as oligoclase basalts.