Band Strengths Research Articles

A New Method for Measuring Infrared Band Strengths in H2O Ices: First Results for OCS, H2S, and SO2

Infrared (IR) band strengths are needed to extract accurate molecular abundances from astronomical observations of interstellar and solar system ices. However, laboratory measurements of such intensities often have required multiple assumptions about ice composition and thickness. Here we describe a method that circumvents most of the common assumptions and uncertainties in IR band-strength determinations. We have applied the method to measure IR band strengths of OCS, H2S, and SO2 in the absence and presence of H2O ice at 10 K, the first measurements of their type. Our results show for the first time that the presence of H2O makes little difference in IR intensities for these three sulfur-containing molecules’ strongest IR features. The immediate application will be to laboratory studies of low-temperature chemistry of interstellar and cometary ices.

Longitudinal Variation of H2O Ice Absorption on Miranda

Many tidally locked icy satellites in the outer solar system show leading/trailing hemispherical asymmetries in the strength of near-infrared (NIR) H2O ice absorption bands, in which the absorption bands are stronger on the leading hemisphere. This is often attributed to a combination of magnetospheric irradiation effects and impact gardening, which can modify grain size, expose fresh ice, and produce dark contaminating compounds that reduce the strength of absorption features. Previous research identified this leading/trailing asymmetry on the four largest classical Uranian satellites but did not find a clear leading/trailing asymmetry on Miranda, the smallest and innermost classical moon. We undertook an extensive observational campaign to investigate variations of the NIR spectral signature of H2O ice with longitude on Miranda’s northern hemisphere. We acquired 22 new spectra with the TripleSpec spectrograph on the ARC 3.5 m telescope and four new spectra with GNIRS on Gemini North. Our analysis also includes three unpublished and seven previously published spectra taken with SpeX on the 3 m IRTF. We confirm that Miranda has no substantial leading/trailing hemispherical asymmetry in the strength of its H2O ice absorption features. We additionally find evidence for an anti-Uranus/sub-Uranus asymmetry in the strength of the 1.5 μm H2O ice band that is not seen on the other Uranian satellites, suggesting that additional endogenic or exogenic processes influence the longitudinal distribution of H2O ice band strengths on Miranda.

Infrared Spectra and Intensities of Amorphous and Crystalline Allene

The infrared (IR) spectra, including spectral intensities, of solid hydrocarbons are of interest to astrochemists and astronomers for the relevance of these compounds to surface chemistry in the outer solar system and beyond. However, although the vibrational modes and IR peak positions of many such compounds have long been studied, much less attention has been paid to the IR intensities needed to quantify both astronomical observations and laboratory results. Here we present mid- and near-IR transmission spectra of a relatively little-studied solid hydrocarbon, allene (1,2-propadiene). Spectra of both amorphous and polycrystalline allene are shown for the first time along with optical constants, band strengths, and absorption coefficients. We also report a density and refractive index (670 nm) for each form of solid allene. A radiation-chemical experiment on allene’s formation is described, as are some applications and suggestions for future work.

Sakurai’s Object revisited: new laboratory data for carbonates and melilites suggest the carrier of 6.9-μm excess absorption is a carbonate

ABSTRACTWe present new room-temperature 1100–1800-cm−1 spectra of melilite silicates and 600–2000-cm−1 spectra of three randomly orientated fine-grained carbonates to determine the possible carrier(s) of a 6.9-μm absorption feature observed in a variety of dense astronomical environments, including young stellar objects and molecular clouds. We focus on the low-mass post-asymptotic giant branch star Sakurai’s Object, which has been forming substantial quantities of carbonaceous dust since an eruptive event in the 1990s. Large melilite grains cannot be responsible for the 6.9-μm absorption feature because the similarly shaped feature in the laboratory spectrum was produced by very low (0.1 per cent by mass) carbonate contamination, which was not detected at other wavelengths. Due to the high band strength of the 6.9-μm feature in carbonates, we conclude that carbonates carry the astronomical 6.9-μm feature. Replacement of melilite with carbonates in models of Sakurai’s Object improves fits to the 6–7-μm Spitzer spectra without significantly altering other conclusions of Bowey’s previous models except that there is no link between the feature and the abundance of melilite in meteorites. With magnesite (MgCO3), the abundance of 25-μm-sized SiC grains is increased by 10–50 per cent and better constrained. The mass of carbonate dust is similar to the mass of polycyclic aromatic hydrocarbon dust. Existing experiments suggest that carbonates are stable below 700 K; however, it is difficult to ascertain the applicability of these experiments to astronomical environments, and more studies are required.

Theoretical study of the helical conformers and ECD spectra of 8-aminoquinoline polymers

In this study, the helical conformers and absorption spectra of three types of 8-aminoquinoline oligoamides were studied. The stable conformers of these oligoamides connected with chiral β-pinene at their terminals were searched, and their dominant conformers and corresponding Boltzmann statistical weights were obtained. The excitation energy and oscillator strength of the dominant conformers were calculated, and the UV and electronic circular dichroism (ECD) spectra were also simulated. β-pinene can form delocalized π-bonds at the C-terminal, which results in a strong R band for CQn. Furthermore, the degree of polymerization also affected the strength of the absorption band for all the oligoamides.

The Infrared Database of Extragalactic Observables from Spitzer. II. The Database and Diagnostic Power of Crystalline Silicate Features in Galaxy Spectra

Abstract We present the Infrared Database of Extragalactic Observables from Spitzer (IDEOS), a homogeneous, publicly available, database of 77 fitted mid-infrared observables in the 5.4–36 μm range, comprising measurements for 3335 galaxies observed in the low-resolution staring mode of the Infrared Spectrometer on board the Spitzer Space Telescope. Among the included observables are polycyclic aromatic hydrocarbon fluxes and their equivalent widths, the strength of the 9.8 μm silicate feature, emission-line fluxes, solid-state features, rest-frame continuum fluxes, synthetic photometry, and a mid-infrared spectral classification. The IDEOS spectra were selected from the Cornell Atlas of Spitzer-IRS Sources. To our surprise, we have detected at a >95% confidence level crystalline silicates in the spectra of 786 IDEOS galaxies. The detections range from single-band detections to detections of all fitted crystalline bands (16, 19, 23, 28, and 33 μm). We find the strength of the crystalline silicate bands to correlate with the amorphous silicate strength and the change from an emission to an absorption feature to occur at higher obscuration as the wavelength of the crystalline silicate band is longer. These observed characteristics are consistent with an origin for the amorphous and crystalline silicate features in a centrally heated dust geometry, either an edge-on disk or a cocoon. We find the 23 and 33 μm crystalline silicate bands to be well suited to classify the obscuration level of galactic nuclei, even in the presence of strong circumnuclear star formation. Based on our detection statistics, we conclude that crystalline silicates are a common component of the interstellar medium of galactic nuclei.

Infrared Spectral Intensities of Amine Ices, Precursors to Amino Acids.

Here, we address the paucity of infrared (IR) spectral data needed to quantify low-temperature experiments with amine ices, such as the formation of amino acids, by reporting new IR results on solid phases of methylamine (CH3NH2) and ethylamine (CH3CH2NH2), precursors to glycine and alanine, respectively. Mid-IR band strengths and absorption coefficients for CH3NH2 and CH3CH2NH2, in both amorphous and crystalline forms, are presented, along with measurements of a density and refractive index (670 nm) for each. For these same compounds, we also have calculated IR optical constants, and they are being made available in electronic form. Some applications of our new results are described along with proposals for future investigations. Suggestions are made related to the methods employed in such work, and particularly to the application of Beer's Law to the IR study of compounds of astrobiological interest. Comments are also included on the methods used, and the results presented in a recently published work on amino-acid IR intensities.

Ammonia Ices Revisited: New IR Intensities and Optical Constants for Solid NH3

Abstract Solid ammonia (NH3) is the only nitrogen-containing polyatomic molecule reported in both interstellar and solar system ices. However, an examination of the literature reveals significant omissions and difficulties in earlier work that can hinder quantitative measurements of solid NH3 by infrared (IR) methods by both astronomical observers and laboratory spectroscopists. Here we reinvestigate the IR spectra of NH3 ices in amorphous and crystalline forms to determine mid- and near-IR intensities. The IR absorption coefficients, band strengths, and optical constants are presented for both amorphous and crystalline NH3, along with new density and refractive index (λ = 670 nm) measurements needed to quantify our IR results. We find that two widely used approximate IR band strengths for amorphous NH3 are nearly 30% higher than measured values after corrections for the compound’s density. We have also used our new results to rescale two NH3 near-IR band strengths in the literature, finding that they increase by about 60%. Some applications of our new results are described along with suggestions for future studies. Optical constants are available in electronic form.

Infrared spectra and optical constants of astronomical ices: IV. Benzene and pyridine

Infrared (IR) spectra of two solid aromatic compounds, benzene (C6H6) and pyridine (C5H5N), have been recorded in their amorphous and crystalline states. Measurements of density and refractive index (λ = 670 nm) are reported for each form of each compound, quantities needed to compute IR intensities and optical constants for use in laboratory experiments and astronomical observations. These are the first such measurements of each compound's density, refractive index, and spectra at temperatures relevant to the outer solar system and interstellar medium, with all measurements being made in a single laboratory. We have used these results to determine both IR band strengths and optical constants for benzene and pyridine ices in amorphous and crystalline forms. Also, the intensity of benzene's IR absorbance near 1477 cm−1 is measured in samples containing H2O-ice and compared to the strength of the same band in anhydrous amorphous benzene, the first comparison of this type for this compound. Suggestions are made for applications and future work related to the chemistry of icy bodies in the Solar System and the interstellar medium.

Infrared Spectroscopy and Photochemistry of Anthracoronene in Cosmic Water Ice.

We present a laboratory study of the polycyclic aromatic hydrocarbon (PAH) anthracoronene (AntCor, C36H18) in simulated interstellar ices in order to determine its possible contribution to the broad infrared absorption bands in the 5–8 μm wavelength interval. The Fourier transform infrared (FTIR) spectrum of AntCor, codeposited with water ice, was collected. The FTIR spectrum of the sample irradiated with ultraviolet photons was also collected. Unirradiated and UV-irradiated AntCor embedded in water ice have not been studied before; therefore, the molecule’s band positions and intensities were compared to published data on AntCor in an argon matrix and theoretical calculations (DFT), as well as the published results of its parent molecules, coronene and anthracene, in water ice. The experimental band strengths for unirradiated AntCor exhibit variability as a function of PAH:H2O concentration, with two distinct groupings of band intensities. AntCor clustering occurs for all concentrations and has a significant effect on PAH degradation rates and photoproduct variability. Near-IR spectra of irradiated AntCor samples show that AntCor+ production increases as the concentration of AntCor in water ice decreases. Photoproduct bands are assigned to AntCor+, cationic alcohols, protonated AntCor, and ketones. We report the rate constants of the photoproduct production for the 1:1280 AntCor:H2O concentration. CO2 production from AntCor is much less than what was previously reported for Ant and Cor and exhibits two distinct regimes as a function of AntCor:H2O concentration. The contribution of AntCor photoproducts to astronomical spectra can be estimated by comparison with the observed intensities in the 7.4–8.0 μm range.

Absorption Spectra and the Electronic Structure of Gallic Acid in Water at Different pH: Experimental Data and Theoretical Cluster Models.

Gallic acid (GA) has been characterized in terms of its optical properties in aqueous solutions at varying pH in experiments and in theoretical calculations by analyzing the protonated and deprotonated forms of GA. This work is part of a series of studies of the optical properties of different carboxylic acids in aqueous media. The experimental electronic spectra of GA exhibit two strong well-separated absorption peaks (B- and C-bands), which agree with previous studies. However, in the current study, an additional well-defined low-energy shoulder band (A-band) in the optical spectra of GA was identified. It is likely that the A-band occurs for other carboxylic acids in solution, but because it can overlap with the B-band, it is difficult to discern. The theoretical calculations based on density functional theory were used to simulate the optical absorption spectra of GA in water at different pH to prove the existence of this newly found shoulder band and to describe and characterize the full experimental optical spectra of GA. Different cluster models were tested: (i) all water molecules are coordinated near the carboxy-group and (ii) additional water molecules near the hydroxy-groups of the phenyl ring were included. In this study, we found that both the polarizable continuum model (dielectric property of a medium) and neighboring water molecules (hydrogen-bonding) play significant roles in the optical spectrum. The results showed that only an extended cluster model with water molecules near carboxy- and hydroxy-groups together with the polarizable continuum model allowed us to fully reproduce the experimental data and capture all three absorption bands (A, B, and C). The oscillator strengths of the absorption bands were obtained from the experimental data and compared with theoretical results. Additionally, our work provides a detailed interpretation of the pH effects observed in the experimental absorption spectra.

Two-dimensional correlation spectroscopy indicates the infrared spectral markers of the optimum scorching degree of rhubarb (Rhei Radix et Rhizoma) to enhance the anti-inflammatory activity

Rhubarb has been used as herbal purgative with a long and worldwide history. But purgation is a side effect of rhubarb in many cases. In traditional Chinese medicine, rhubarb can be stir-baked to scorch to attenuate the purgative function while enhance other bioactivities such as the anti-inflammatory effect. However, the over-scorched rhubarb will lose necessary active ingredients and even generate toxic ingredients. Nowadays, the scorching degree of rhubarb is still determined by the intuitive observation of color changes in production. Therefore, this research was designed to develop more reasonable and objective criteria to evaluate the scorching degree to ensure the efficacy, safety and consistency of the scorched rhubarb. Taking the example of the rhubarb baked at 200 °C for different times, the combination of trait indicator (color), chemical indicator (combined and free AQs, sennosides, gallic acid, 5-HMF) and biological indicator (anti-inflammatory) showed that the rhubarb baked for 30 min can be treated as the right scorched. Two-dimensional correlation spectroscopy helped to reveal the infrared spectral markers of the water extract near 1694 cm−1, 1442 cm−1 and 825 cm−1, as well as the relative strength of the absorption bands of the powder near 1610 cm−1 and 1020 cm−1, to discriminate the right-scorched and over-scorched rhubarb. In conclusion, the combination of trait, chemical and biological indicators can provide reasonable and objective criteria for the optimum scorching degree of rhubarb, while FTIR spectroscopy can assess the right endpoint of the scorching process in a rapid, cheap and green way.

Sensitivity of the electronic and topological properties of tetradymites upon atomic mutations

The tetradymite compounds are known as good thermoelectric materials and also strong topological insulators, which exhibit unique electronic structures governed by several essential material features such as containing heavy elements and having small band gap. Here we demonstrate by first-principles calculations that for a given alloyed tetradymite, its topological nature actually shows certain sensitivity on the detailed atomic configurations, even if all of them have the same stoichiometric composition. Specifically, some tetradymites are found to be robust topological insulators (or normal insulators) upon arbitrary atomic mutations, which however can induce transition from topologically trivial to non-trivial or vice versa for other tetradymites. The underlying physical mechanisms are discussed in terms of the band gaps and strength of spin–orbit coupling in some exampling tetradymites.

A CO2 Cycle on Ariel? Radiolytic Production and Migration to Low-latitude Cold Traps

Abstract CO2 ice is present on the trailing hemisphere of Ariel but is mostly absent from its leading hemisphere. The leading/trailing hemispherical asymmetry in the distribution of CO2 ice is consistent with radiolytic production of CO2, formed by charged particle bombardment of H2O ice and carbonaceous material in Ariel’s regolith. This longitudinal distribution of CO2 on Ariel was previously characterized using 13 near-infrared reflectance spectra collected at “low” sub-observer latitudes between 30°S and 30°N. Here we investigated the distribution of CO2 ice on Ariel using 18 new spectra: 2 collected over low sub-observer latitudes, 5 collected at “mid” sub-observer latitudes (31°N–44°N), and 11 collected over “high” sub-observer latitudes (45°N–51°N). Analysis of these data indicates that CO2 ice is primarily concentrated on Ariel’s trailing hemisphere. However, CO2 ice band strengths are diminished in the spectra collected over mid and high sub-observer latitudes. This sub-observer latitudinal trend may result from radiolytic production of CO2 molecules at high latitudes and subsequent migration of this constituent to low-latitude cold traps. We detected a subtle feature near 2.13 μm in two spectra collected over high sub-observer latitudes, which might result from a “forbidden” transition mode of CO2 ice that is substantially stronger in well-mixed substrates composed of CO2 and H2O ice, consistent with regolith-mixed CO2 ice grains formed by radiolysis. Additionally, we detected a 2.35 μm feature in some low sub-observer latitude spectra, which might result from CO formed as part of a CO2 radiolytic production cycle.

Infrared analysis of Valine degradation by keV electrons. Measurements and CASINO-extended model predictions

ABSTRACTDegradation of L-valine by 0.06–1.0-keV electron beams is analysed in laboratory, at 10, 150, and 300 K. Valine film thicknesses are measured by profilometry, permitting band strength determination for selected valine bands. The column density evolutions during the irradiation are measured via infrared spectroscopy and destruction cross-sections are extracted; the latter range from 1–100 × 10−16 cm2. Data show that, in general, destruction cross-sections depend not only on projectile energy and sample temperature but also on sample thickness and beam fluence. In order to understand these findings, a statistical model is proposed for describing the radiolysis of organic materials. Comparing predictions with experimental results for valine, the main trends are reproduced. The quantitative disagreement indicates that it is necessary to include sputtering in the model. A major contribution of the model is to permit to simulate, layer by layer, the sample degradation rate as a function of fluence. The model assumes that the destruction cross-section of precursor molecules is proportional to the local stopping power and uses the Monte Carlo CASINO code to determine the deposited energy distribution in the bulk. As astrophysical implications, the radiolysis of valine dissolved in H2O ice and shielded by a CO2 layer is predicted, as an attempt to analyse the degradation of realistic cosmic materials by keV electrons.

Absolute Absorption Cross Section and Orientation of Dangling OH Bonds in Water Ice

Abstract The absolute absorption cross section of dangling OH bonds in water ice, a free OH stretch mode by three-coordinated surface water molecules, is derived experimentally as 1.0 ± 0.2 × 10−18 cm2 at 3696 cm−1 for amorphous water at 90 K using infrared multiple-angle incidence resolution spectrometry (IR–MAIRS). The integrated absorption cross section (band strength) of the dangling OH bond at 90 K (1.4 ± 0.3 × 10−17 cm molecule−1 at 3710–3680 cm−1) is found to be more than 1 order of magnitude smaller than those in bulk ice or liquid water. This indicates that a lack of hydrogen-bonding significantly decreases the band strength of dangling OH bonds. The present study also provides average molecular orientations of dangling OH bonds at 10 K and 90 K, because both the surface-parallel (in-plane) and surface-perpendicular (out-of-plane) vibration spectra of dangling OH bonds are quantitatively measured by IR–MAIRS. The intensity ratio of the dangling-OH peaks between in-plane to out-of-plane spectra shows the isotropic nature (random orientation) of the two- and three-coordinated dangling OH bonds in microporous amorphous water prepared at 10 K; however, the three-coordinated dangling OH bonds in nonporous amorphous water prepared at 90 K are dominantly located at the top ice surface and oriented perpendicular to it. These findings provide fundamental insights into the relationship between the structure and optical properties of ice surfaces, and aid quantitative understanding of the surface structure of interstellar ices and their laboratory analogs.

The Infrared Complex Refractive Index of Amorphous Ammonia Ice at 40 K (1.43–22.73 μm) and Its Relevance to Outer Solar System Bodies

Abstract A near-IR absorption band at 2.2 μm linked to ammonia-containing ice has been detected on icy bodies throughout the solar system and appears in the extensive volume of data for Pluto and Charon returned by New Horizons. This band is an important clue for understanding the abundance of ammonia and ammoniated compounds on the surface of outer solar system bodies and requires new laboratory data for its full analysis. To satisfy this data need, the complex refractive index of amorphous ammonia ice was calculated from experimental infrared transmission spectra with ice deposition and measurements conducted at 40 K, a characteristic surface temperature for outer solar system bodies. The measured imaginary part of the complex refractive index and associated band strength calculations are generally larger than prior published values for amorphous ammonia ice at 30 K. The complex refractive index for amorphous ammonia at 40 K computed in the mid-infrared region (2.5–22.73 μm) will also be valuable for interpreting observations of both solar system and astrophysical sources anticipated with the Near InfraRed Spectrograph and Mid-Infrared Instrument on the James Webb Space Telescope.

Comparative Analysis of the Mechanical Properties of Polymer Matrix Composites Reinforced with Fiberglass Fabric

The composites materials are increasingly displacing the traditional ones and are the most widely used of all groups of engineering materials. Polymer matrix composites have the greatest application and they are used for equipment operating in the sea-water environment and polymer pipes. In this article, the mechanical properties of six types of polymer matrix composites reinforced with fiberglass fabric are considered and analyzed. Two types of resin were used for the matrix – polyester resin and vinyl ester resin. The both types of matrices are reinforced with three different fiberglass fabric- monoaxial, biaxial and triaxial fiberglass. The investigated composites are obtained by mechanical pressing in the form of sixlayer panels. A comparative analysis of tensile strength and banding strength of the six types investigated composites was made. A macrofractographic analysis of the structure was also performed.

Infrared detection of Criegee intermediates

AbstractIn this mini‐review article, we present the recent progress of utilizing three types of infrared (IR) spectroscopic tools to investigate the chemistry of Criegee intermediates (CIs). The first part of this article described a recent work of Wang et al., which utilized rapid‐scan FTIR to detect CIs created from ozonolysis. The second part of this article describes the advantages of quantum cascade lasers (QCLs) used as novel IR spectroscopic tools to probe CIs and the key concepts of experimental implementations. We also summarize the works of Chang and co‐workers, which utilized distributed feedback QCLs with thermal chirping to detect the simplest CI, CH2OO, and the subsequent kinetics measurements, such as reactions of CH2OO with ozone, CH3SH, and dimethyl sulfoxide. In the last part of this article, we described the key ideas of external‐cavity QCLs coupled with off‐axis integrated cavity output spectroscopy, which was proposed by Chung et al., and also the latest progress on determination of the band strength of CH2OO and its rate coefficient with O3.

Crystalline ices – Densities and comparisons for planetary and interstellar applications

Results are presented from recent density measurements on twenty-nine crystalline ices at temperatures applicable to the outer Solar System and the interstellar medium. For each ice we report both a density and a refractive index at 670 nm, quantities needed to calculate infrared band strengths, complex indices of refraction, and, ultimately, molecular abundances. Comparisons are made between densities obtained from micrometer-size crystalline ice samples prepared by vapor-phase deposition and the larger crystals (mm scale) used in diffraction work, and often made by the slow cooling of a liquid or a vapor in a sealed capillary tube. A strong positive correlation is found between the two sets of crystalline-ice densities.