NIST Database Research Articles

Numerical techniques for infrared spectra analysis of organic and inorganic volatile compounds for biomedical applications

We consider the possibility of using a combination of machine and deep learning in the spectral analysis for multicomponent gas mixtures. The experimental setup consists of a quantum cascade laser with a tuning range of 5.3 to 12.8 μm, a peak power up to 150 mW, and a Herriot astigmatic gas cell with an optical path of up to 76 m. We used acetone, ethanol, methanol, acetaldehyde, and ethylene as test substances for the described techniques. For detection and clustering biomarkers, we used machine learning methods such as t-distributed stochastic neighbor embedding, principal component analysis, and classification methods such as decision tree, k-nearest neighbors, logistic regression, and support vector machines. We used a shallow convolutional neural network (CNN) based on TensorFlow (Google) and Keras for spectral analysis of gas mixtures. We modeled IR spectra of pure substances using an NIST database as training and validation sets. Then we used experimental spectra as a test set. We showed that logistic regression gives us the best result for pure substances’ classification. Next, we modeled gas mixtures from synthetic IR spectra for CNN as training and validation sets. We showed that neural networks trained on synthetic spectra can recognize synthetic gas mixtures and experimental individual gaseous substances. We suggest using machine learning methods for pure substances clustering and classification and CNN for gas mixture components identification. We experimentally obtained minimum detectable concentration at ppm level for pure substances. Finally, we estimated that detection limits for the described experimental setup and numerical techniques occurs at levels around 10 to 50 ppb.

An Updated Formalism for Line-driven Radiative Acceleration and Implications for Stellar Mass Loss

Abstract Radiation contributes to the acceleration of large-scale flows in various astrophysical environments because of strong opacity in the spectral lines. Quantification of the associated force is crucial to understanding these line-driven flows, and a large number of lines (due to the full set of elements and ionization stages) must be taken into account. Here we provide new calculations of the dimensionless line strengths and associated opacity-dependent force multipliers for an updated list of approximately 4.5 million spectral lines compiled from the NIST, CHIANTI, CMFGEN, and TOPbase databases. To maintain generality of application to different environments, we assume local thermodynamic equilibrium, illumination by a Planck function, and the Sobolev approximation. We compute the line forces in a two-dimensional grid of temperatures (i.e., values between 5200 and 70,000 K) and densities (varying over 11 orders of magnitude). Historically, the force multiplier function has been described by a power-law function of optical depth. We revisit this assumption by fitting alternate functions that include saturation to a constant value (Gayley’s Q ¯ parameter) in the optically thin limit. This alternate form is a better fit than the power-law form, and we use it to calculate example mass-loss rates for massive main-sequence stars. Because the power-law force multiplier does not continue to arbitrarily small optical depths, we find a sharp decrease, or quenching, of line-driven winds for stars with effective temperatures less than about 15,000 K.

The ExoMolOP database: Cross sections andk-tables for molecules of interest in high-temperature exoplanet atmospheres

Here we present a publicly available database of opacities for molecules of astrophysical interest named ExoMolOP that has been compiled for over 80 species, and is based on the latest line list data from the ExoMol, HITEMP, and MoLLIST databases. These data are generally suitable for characterising high-temperature exoplanet or cool stellar and substellar atmospheres, and have been computed at a variety of pressures and temperatures, with a few molecules included at room temperature only from the HITRAN database. The data are formatted in different ways for four different exoplanet atmosphere retrieval codes; ARCiS, TauREx, NEMESIS, and petitRADTRANS, and include both cross sections (atR=λ/Δλ= 15000) andk-tables (atR=λ/Δλ= 1000) for the 0.3–50μm wavelength region. Opacity files can be downloaded and used directly for these codes. Atomic data for alkali metals Na and K are also included, using data from the NIST database and the latest line shapes for the resonance lines. Broadening parameters have been taken from the literature where available, or have been estimated from the parameters of a known molecule with similar molecular properties where no broadening data are available.

Изучение кинетики реакции нуклеофильного замещения 7-амино-3-трет-бутил-4-оксо-8-циано-6Н-пиразоло[5,1-с][1,2,4]-триазина хлористым бензилом

The purpose of the study.The aim of the work was to study the kinetics of the nucleophilic substitution reaction be-tween 7-amino-3-tert-butyl-4-oxo-8-cyano-6H-pyrazolo[5,1-c][1,2,4]-triazine and benzyl chloride. Research methods.7-amino-1-benzyl-3-tert-butyl-4-oxo-8-cyano-6H-pyrazolo[5,1-c][1,2,4]-triazine was synthesized by the nucleophilic substitution reaction by the interaction of 7-amino-3-tert-butyl-4-oxo-8-cyano-6h-pyrazolo[5,1-c][1,2,4]-triazine with benzyl chloride. The IR spectra of the initial and obtained compounds were obtained using the Agilent Cary 660 FTIR IR-Fourier spectrometer. UV spectra were taken on a Shimadzu UV-1800 spectrophotometer and a digital STUART Melting point SMP30 device with a resolution of 0.10С was used to determine the melting temperature. Kinetic control of the process under study was carried out by TLC (planar chromatography). During the analysis, Sorbfil PTSH-AF-V-UV chromatographic plates with high efficiency were used. The chromatograms were developed at a wavelength of 254 nm using a SORBFIL video sensor based on a lighting camera. Chromatograms were processed in the computer program "Sorbflil TLC View 1.8". Results.The interaction of 7-amino-3-tert-butyl-4-oxo-8-cyano-6H-pyrazolo[5,1-c][1,2,4]-triazine and benzyl chloride PhCH2Cl produced a white crystalline substance with Tpl =194,6-195,20C. The yield of the product was 1,1g (79% of the theoretical). When analyzing the IR spectrum of the obtained compound, the presence in its structure was revealed: 1,2,4-triazine ring (at 943 and 1096 cm-1 peaks characteristic of the "skeletal vibrations" of the triazine ring were detected); pyrazole ring (peaks at 1591 and 1350 cm-1), NH2 groups (at 3202 cm-1, a peak corresponding to the valence vibrations of the amino group was manifested), C≡N groups (peak at 2220 cm-1), C=O groups (peak at 1702 cm-1), groups with (4)=O (peak at 1626 cm-1). The existence of peaks of the benzyl group is analyzed using the NIST database. Transitions were observed in the UV spectrum at 255nm (π→σ* transition of the functional group C=O) and 318 nm (π→π* transition of the aromatic system). To determine the kinetic parameters of the reaction, the data obtained using the TLC method were processed using differential and integral methods, as well as the Van't-Hoff method. Conclusion. During kinetic studies, it was found that the nucleophilic substitution between 7-amino-3-tert-butyl-4-oxo-8-cyano-6H-pyrazolo[5,1-c][1,2,4]-triazine and benzyl chloride has that the reaction order is 0,9, the rate constant is 0.0064 min-1.

Gas chromatography coupled with mass spectrometry for the rapid characterization and screening of volatile oil of euphorbia fischeriana steud

Gas chromatography (GC)-mass spectrometry is a powerful tool which is used in the analysis of volatile components in food and herbal medicine. Euphorbia fischeriana Steud., a traditional Chinese herb, has been used for thousands of years in China. Recently, scientists are exploring more on the pharmacological action of E. fischeriana. However, so far, there is no information regarding the volatile constituents of E. fischeriana. Therefore, in this study, we aimed to investigate and characterize the global chemical ingredients of volatile oil of E. fischeriana under in vitro and in vivo conditions. In this study, an accurate and rapid GC combined with the mass spectrometric method and MassHunter tool were employed to identify the comprehensive constituents and explored the absorbed components in rat serum after oral administration of E. fischeriana. According to our results, a total of 28 compounds were identified via in vitro analysis by matching with the NIST database. Of them, the following 14 compounds were tentatively characterized in the serum samples: (−)-alpha-cedrene; (+/-)-sesquithuriferone; cedrol; acorenone; neocembrene; geranylgeraniol; abietatriene; abieta-7,13-diene; cembrenol; sclareol; ethyl linoleate; isopimara-7,15-dien-3-one; abietadienal; and abietinol. Most of the compounds identified were diterpenes and sesquiterpenes. These results might be useful in various pharmacological and pharmacodynamic research, and the established method could offer valuable chemical information for bioactive volatile components characterization.

The fully relativistic multi-configuration Dirac–Hartree–Fock method for atomic structure calculations for multiply charged ions: the example of Ca XV

In this work, fully relativistic multi-configuration Dirac–Hartree–Fock approach for calculating atomic structure parameters has been presented and compared to other approaches such as Hartree–Fock pseudo-Relativistic (HFR) method. As an example of application, results of fully relativistic calculations for the ion Ca XV have been obtained and compared to Hartree–Fock pseudo-relativistic calculations and to NIST database values.This example is important for plasma diagnostic and astrophysical studies because Ca XV atomic data of high accuracy are still very scarce.

Effects of anion and alkyl chain length of cation on the thermophysical properties of imidazolium-based ionic liquid

Abstract This study focused on the effects of anions and the alkyl chain length of cations on the thermophysical properties of imidazolium-based ionic liquid (ILs). The data were obtained from references and the NIST database. The studied parameters include the melting temperature (Tm), glass transition temperature (Tg), decomposition temperature (Td), enthalpy of fusion (ΔHm), and thermal conductivity ( λ ). The variations of Tm with the anions in [C16MIM][A] where A = Br, Cl, BF4, PF6, and TFO, generally decreased with increasing anion radius, except for A = PF6, due to strong hydrogen bonds for the sake of an F atom. The values of the critical temperatures (Tm, Tg, and Td) generally show a strong variation with the number of carbon atom or alkyl chain length (the number of n in [CnMIM][A] for A = BF4, NTf2, and PF6). The variation of Tm corresponding to n shows non-monotonous variations. This characteristic is the result of the combination of interaction potentials in the crystalline and liquid phases. The variation of Tg corresponding to n shows even–odd alternation, presumably due to the competition between the electrostatic and van der Waals forces. Many types of ILs have a relatively high Td value, enabling them to remain in the liquid state above 400 °C, they have excellent catalytic activity and dynamic properties. The variation of Td with n appears different to that of Tm. Furthermore, the variation of ΔHm with n seems to follow that of Tm. This behaviour is in accordance with the thermodynamic relation between ΔHm, Tm, and the entropy of the system. The values of λ varied weakly with the alkyl chain length, and strongly depend on the type of anion.

Energy levels and transition probabilities of N+, F3+, and Ne4+ ions

Abstract Term energies, oscillator strengths, transition probabilities, and transition wavelengths among the low-lying states of (1s2)2s22p2, 2s22p3p, 2s2p3, 2s22p3s, and 2s22p3d 1,3,5 L L = S, P, D, F in N+, F3+, and Ne4+ ions were calculated by using the multiconfiguration Rayleigh-Ritz variation method and restricted variation method. The transition oscillator strengths and transition probabilities for the electric dipole transitions are both given in length and velocity gauges. Deviations between these two gauge values are discussed. The calculated atomic parameters are in good agreement with the observed experimental results and other theoretical data. Furthermore, the uncertainty of each electric dipole transition is estimated. Several uncertainties of transition parameters are improved when comparing with values from national institute of standards and technology NIST database. Atomic parameters presented in this paper should be useful for identifying the levels as well as for precise spectral modeling in astrophysical and laboratory plasmas in the future work.

Spectroscopic plasma diagnosis of V2O5 at a Variable of Operating Power and Pressure With Radio Frequency Magnetron Sputtering

In this paper, we investigate the basic characteristics of “magnetron sputtering plasma” using the target V2O5. The “magnetron sputtering plasma” is produced using “radio frequency (RF)” power supply and Argon gas. The intensity of the light emission from atoms and radicals in the plasma measured by using “optical emission spectrophotometer”, and the appeared peaks in all patterns match the standard lines from NIST database and employed are to estimate the plasma parameters, of computes electron temperature and the electron density. The characteristics of V2O5 sputtering plasma at multiple discharge provisos are studied at the “radio frequency” (RF) power ranging from 75 - 150 Watt and gas pressure (0.1, 0.08) mbar. One can observe that the intensity of the emission lines increases with increasing the sputtering power. We find that the electron temperature excess drastically from 0.95 eV to 1.11eV when the emptying gas pressure excess of 0.1 to 0.08 mbar. On the other hand the excess electron temperature from 0.9 to 1.01 eV with increasing sputtering power from 100 to 125 Watt, while the electron density decrease from 5.9×1014 to 4.5×1014 cm−3 with increasing sputtering power. and electron density decrease with increasing of pressure from 4.25×1014 to 2.80×1014 cm−3, But the electron density maximum values 5.9×1014 at pressure 0.08 mbar.

Investigation of the Zeeman—hyperfine structure of atomic niobium

Laser spectroscopy was used for the investigation of the Zeeman-hf structure of 22 lines of atomic niobium in the visible region between 573.7 and 649.4 nm. We used two methods of laser absorption spectroscopy: laser induced fluorescence (LIF) method and optogalvanic spectroscopy (OG). The source of niobium atoms was a hollow cathode discharge tube. The magnetic field of approximately 800 G was generated by a permanent neodymium magnet. We determined experimentally for the first time the Lande gJ factors for 10 levels. We also verified earlier experimental data on the hf structure as well as data from the NIST database regarding Lande gJ factors.

Predicting in silico electron ionization mass spectra using quantum chemistry

Compound identification by mass spectrometry needs reference mass spectra. While there are over 102 million compounds in PubChem, less than 300,000 curated electron ionization (EI) mass spectra are available from NIST or MoNA mass spectral databases. Here, we test quantum chemistry methods (QCEIMS) to generate in silico EI mass spectra (MS) by combining molecular dynamics (MD) with statistical methods. To test the accuracy of predictions, in silico mass spectra of 451 small molecules were generated and compared to experimental spectra from the NIST 17 mass spectral library. The compounds covered 43 chemical classes, ranging up to 358 Da. Organic oxygen compounds had a lower matching accuracy, while computation time exponentially increased with molecular size. The parameter space was probed to increase prediction accuracy including initial temperatures, the number of MD trajectories and impact excess energy (IEE). Conformational flexibility was not correlated to the accuracy of predictions. Overall, QCEIMS can predict 70 eV electron ionization spectra of chemicals from first principles. Improved methods to calculate potential energy surfaces (PES) are still needed before QCEIMS mass spectra of novel molecules can be generated at large scale.

Identifying an unknown compound in flue gas of semiconductor industry – Forensics of a perfluorocarbon

This study investigated the source of a false positive signal in the measurement of total non-methane organic compounds (TNMOCs) by an on-line analyzer based on flame ionization detection (FID) in the flue gas released from a semiconductor fabrication plant. Since no release of volatile organic compounds (VOCs) into the waste gas stream in acid/base ventilation was assured by the plant authority, the positive detection of VOCs became a subject of dispute. In addition to the TNMOC analysis of 5 samples, the investigation used the method that coupled thermal desorption (TD) with gas chromatography mass spectrometry (GC/MS), dubbed TD-GC/MS, to identify the substance that produced the FID signals of TNMOCs. The waste gas was collected with sampling canisters and analyzed by in-laboratory TD-GC/MS. However, mass scanning from 45 to 250 m/z to remove interference from air matrix of O2, N2 and CO2 forbid detecting any ion fragments smaller than 45 m/z and, thus, led to poor match in mass (MS) library search. As a result, a highly retentive porous layer open tubular (PLOT) capillary column was employed to separate the unknown away from the air peak. The success of acquiring all key ion fragments of 31, 50, 69, and 131 m/z resulted in an excellent match with octafluorocyclobutane (C4F8) in the NIST database. A gas standard was then prepared and injected to confirm the identity of C4F8 by the identical mass spectrum and GC retention time. The concentrations of C4F8 found in the 5 flue gas samples varying from 3.32 to 6.21 ppmv were very close to the NMOC range of 3.48–6.62 ppmv as reported by the TNMOC analyzer, proving that the FID signals observed from TNMOC method were mostly produced from C4F8. Consequently, the method of TD-GC/MS would be an ideal method to pre-screen the presence of PFCs before a non-distinguishable TNMOC analyzer is applied to approximate the VOC level as part of the integrated effort to monitor VOC in flue gas.

General Design and Thermodynamic Analysis of a Supercritical Carbon Dioxide Cannon

This paper presents a new supercritical carbon dioxide (SCO2) cannon based on the carbon dioxide (CO2)’s thermodynamic cycle under constant volume. First, Virial equation and NIST database are applied to formulate SCO2’s property and analyze the thermodynamic cycle, which is aimed to get the optimization equation using the cannon’s exit velocity as objective function. Then the cannon’s structural parameters, such as diaphragm thickness and barrel length, and CO2’s filling mass, are optimized. Finally, the flow field and velocity’s change during the launch process is performed with FLUENT. In field test, the ultra-high pressure sensor and ultra-high speed camera are used to measure the pressure distribution along the barrel’s axial direction and the projectile’s exit velocity under different conditions. The results show that all the performance indexes meet the design requirement. The innovative SCO2 cannon in this paper has obvious advantages such as high safety, low cost and fast loading, which can be applied in many situations such as disaster relief, peacekeeping and anti-terrorism. Moreover, the unique energy storage method and thermodynamic design ensure its subsequent development.

Analysis of Ilmenite Slag Using Laser-Induced Breakdown Spectroscopy

The feasibility of using laser-induced breakdown spectroscopy (LIBS) for the compositional analysis of ilmenite slag was explored. The slag was obtained from a pilot-scale ilmenite smelting furnace. The composition of major oxides TiO2, FeO, and MgO are determined by the calibrated LIBS method. LIBS measurements are done under normal atmosphere and temperature. A Q-switched Nd:YAG laser operating at 355 nm was used to create a plasma on an ilmenite slag sample. The characteristic lines based on the NIST database of Fe, Mg, and Ti can be identified on the normalized LIBS spectra for the slag samples. The spectral range chosen for the study is 370 to 390 nm. Calibration curves were plotted using the data collected from various industrial ilmenite samples of varying compositions of TiO2, FeO, and MgO. The univariate simple linear regression technique was used to do the analysis and the prediction accuracy was checked by the root mean square error (RMSE). To validate the application of LIBS, both qualitative and quantitative analysis is done and compared to the analytical ICP-OES results. The model predicts the magnesium content with the highest accuracy and gives good prediction for iron and titanium content. This study demonstrates the capability of using LIBS for the surface analysis of the ilmenite slag sample.

Fourier-Transform VUV Spectroscopy of 14,15N and 12,13C

Accurate Fourier-transform spectroscopic absorption measurements of vacuum ultraviolet transitions in atomic nitrogen and carbon were performed at the Soleil synchrotron. For 14N, transitions from the 2s22p34S3/2 ground state and from the 2s22p32P and 2D metastable states were determined in the 95–124 nm range at an accuracy of 0.025cm−1. The combination of these results with data from previous precision laser experiments in the vacuum ultraviolet range reveals an overall and consistent offset of −0.04 cm−1 from values reported in the NIST database. The splittings of the 2s22p34S3/2 – 2s2p44PJ transitions are well-resolved for 14N and 15N and the isotope shifts determined. While excitation of a 2p valence electron yields very small isotope shifts, excitation of a 2s core electron results in large isotope shifts, in agreement with theoretical predictions. For carbon, six transitions from the ground 2s22p23PJ and 2s22p3s3PJ excited states at 165 nm are measured for both 12C and 13C isotopes.

Tungsten-based material as promising new lead-free gamma radiation shielding material in nuclear medicine.

The main objective of this study was to evaluate the efficacy of tungsten carbide as new lead-free radiation shielding material in nuclear medicine by evaluating the attenuation properties. The elemental composition of tungsten carbide was analysed using Field-Emission Scanning Electron Microscopy (FESEM) with energy dispersive X-ray (EDX). The purity of tungsten carbide was 99.9%, APS: 40-50µm. Three discs of tungsten carbide was fabricated with thickness of 0.1cm, 0.5cm and 1.0cm. Three lead discs with similar thickness were used to compare the attenuation properties with tungsten carbide discs. Energy calibration of gamma spectroscopy was performed by using 123I, 133Ba, 152Eu, and 137Cs. Gamma radiation from these sources were irradiated on both materials at energies ranging from 0.160MeV to 0.779MeV. The experimental attenuation coefficients of lead and tungsten carbide were compared with theoretical attenuation coefficients of both materials from NIST database. The half value layer and mean free path of both materials were also evaluated in this study. This study found that the peaks obtained from gamma spectroscopy have linear relationship with all energies used in this study. The relative differences between the measured and theoretical mass attenuation coefficients are within 0.19-5.11% for both materials. Tungsten carbide has low half value layer and mean free path compared to lead for all thickness at different energies. This study shows that tungsten carbide has high potential to replace lead as new lead-free radiation shielding material in nuclear medicine.

Measuring the oscillator strength of intercombination lines of helium-like V ions in a laser-produced-plasma

We present results of measurements of the oscillator strength of intercombination lines of He-like Vanadium ions in high energy density (HED) laser-produced-plasmas and compare them with the simulations from commonly used codes and data from the NIST database. Whilst not yet sufficiently accurate to constrain different trusted atomic-physics models for the particular system studied, our results are in agreement with the available data within experimental error bars, yet differ from cruder approximations of the oscillator strength used in certain atomic-kinetics packages, suggesting that this general method could be further extended to be used as a measurement of the oscillator strength of additional atomic transitions under the extreme conditions that are achieved in HED experiments.

Investigation of a Collisional Radiative Model for Laser-Produced Plasmas

Plasmas of a variety of types can be described by the collisional radiative (CR) model developed by Colombant and Tonan. From the CR model, the ion distribution of a plasma at a given electron temperature and density can be found. This information is useful for further simulations, and due to this, the employment of a suitable CR model is important. Specifically, ionization bottlenecks, where there are enhanced populations of certain charge states, can be seen in these ion distributions, which in some applications are important in maintaining large amounts of a specific ion. The present work was done by implementing an accepted CR model, proposed by Colombant and Tonon, in Python and investigating the effects of variations in the ionization energy and outermost electron subshell occupancy term on the positions of ionization bottlenecks. Laser Produced Plasmas created using a Nd:YAG laser with an electron density of ∼ne = 1021 cm−3 were the focus of this work. Plots of the collisional ionization, radiative recombination, and three-body recombination rate coefficients as well as the ion distribution and peak fractional ion population for various elements were examined. From these results, it is evident that using ionization energies from the NIST database and removing the orbital occupancy term in the CR model produced results with ionization bottlenecks in expected locations.

Electron Impact Excitation of Singly Charged Indium Ion

We study electron impact excitation of In\({}^{+}\) using relativistic distorted wave method and report cross sections for 37 transitions among the fine-structure levels of \(5s^2\), \(5s5p\), \(5s5d\), \(5s6s\) and \(5s6p\) configurations at the scattered electron energies upto 200 eV. The bound state wavefunctions of the target ion are obtained within multi-configuration Dirac-Fock approach. Our calculated oscillator strengths are compared with the results from the NIST database and other theoretical calculations. Cross sections are fitted with an analytical formula and the fitting parameters are made available for their possible applications in plasma modeling.

Decomposition pathway and kinetic analysis of perfluoroketone C5F10O

Recently, perfluoroketone C5F10O has been seen as a promising alternative gas for sulphur hexafluoride (SF6), of which the global warming potential (GWP) is extremely high. C5F10O has a good insulation property and the GWP value is only 1, thus can be used as insulation medium in gas-insulated switchgears. In this study, the decomposition pathway of C5F10O and the recombination processes of free radicals are firstly explored. Secondly, the rate constants of the reactions are calculated based on the variational transition state theory, which then are fitted in the NIST form. The results not only provide the basic data for the chemical kinetics calculations, but also supplementary data for the NIST database. Finally, the chemical kinetic calculations are performed to study the decomposition characteristics at 400 °C and 700 °C. Only 4% C5F10O decomposes at 400 °C, while 96% decomposes at 700 °C. The stable products like CO, C2F4, C2F6, C3F6 are formed. The mole fraction of CF4 is above 10–10 at 400 °C. A certain amount of C2F2 is produced at 700 °C. Besides, precise chemical kinetic composition results at steady state during the thermal decomposition of C5F10O are obtained. By analyzing the energy change of reactions, the formation of products is explained theoretically. The results not only reveal the decomposition mechanism of C5F10O and recombination mechanism of the stable products, but also provide the guidance for electrical engineering.