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Muonium is an exotic atom made up of an antimuon and an electron, which was discovered in 1960 by Vernon W. Hughes and is given the chemical symbol Mu. During the muon's 2.2 µs lifetime, muonium can undergo chemical reactions. Because, like a proton, the antimuon's mass is vastly larger than that of the electron, muonium is more similar to atomic hydrogen than positronium. Its Bohr radius and ionization energy are within 0.5% of hydrogen, deuterium, and tritium, and thus it can usefully be considered as an exotic light isotope of hydrogen.
Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum.
Raman spectroscopy is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified.
Chemometrics is the science of extracting information from chemical systems by data-driven means. Chemometrics is inherently interdisciplinary, using methods frequently employed in core data-analytic disciplines such as multivariate statistics, applied mathematics, and computer science, in order to address problems in chemistry, biochemistry, medicine, biology and chemical engineering. In this way, it mirrors other interdisciplinary fields, such as psychometrics and econometrics.
A mass spectrum is a histogram plot of intensity vs. mass-to-charge ratio (m/z) in a chemical sample, usually acquired using an instrument called a mass spectrometer. Not all mass spectra of a given substance are the same; for example, some mass spectrometers break the analyte molecules into fragments; others observe the intact molecular masses with little fragmentation. A mass spectrum can represent many different types of information based on the type of mass spectrometer and the specific experiment applied. Common fragmentation processes for organic molecules are the McLafferty rearrangement and alpha cleavage. Straight chain alkanes and alkyl groups produce a typical series of peaks: 29 (CH3CH2+), 43 (CH3CH2CH2+), 57 (CH3CH2CH2CH2+), 71 (CH3CH2CH2CH2CH2+) etc.
In Raman spectroscopy, the depolarization ratio is the intensity ratio between the perpendicular component and the parallel component of Raman scattered light.
In particle physics, the quantum yield of a radiation-induced process is the number of times a specific event occurs per photon absorbed by the system.
Naturally occurring tungsten (74W) consists of five isotopes. Four are considered stable (182W, 183W, 184W, and 186W) and one is slightly radioactive, 180W, with an extremely long half-life of 1.8 ± 0.2 exayears (1018 years). On average, two alpha decays of 180W occur per gram of natural tungsten per year, so for most practical purposes, 180W can be considered stable. Theoretically, all five can decay into isotopes of element 72 (hafnium) by alpha emission, but only 180W has been observed to do so. The other naturally occurring isotopes have not been observed to decay (they are observationally stable), and lower bounds for their half-lives have been established:
Natural hafnium (72Hf) consists of five observationally stable isotopes (176Hf, 177Hf, 178Hf, 179Hf, and 180Hf) and one very long-lived radioisotope, 174Hf, with a half-life of 7.0×1016 years. In addition, there are 34 known synthetic radioisotopes, the most stable of which is 182Hf with a half-life of 8.9×106 years. This extinct radionuclide is used in hafnium–tungsten dating to study the chronology of planetary differentiation.
Mass spectrometry is a scientific technique for measuring the mass-to-charge ratio of ions. It is often coupled to chromatographic techniques such as gas- or liquid chromatography and has found widespread adoption in the fields of analytical chemistry and biochemistry where it can be used to identify and characterize small molecules and proteins (proteomics). The large volume of data produced in a typical mass spectrometry experiment requires that computers be used for data storage and processing. Over the years, different manufacturers of mass spectrometers have developed various proprietary data formats for handling such data which makes it difficult for academic scientists to directly manipulate their data. To address this limitation, several open, XML-based data formats have recently been developed by the Trans-Proteomic Pipeline at the Institute for Systems Biology to facilitate data manipulation and innovation in the public sector. These data formats are described here.
An aglycone is the chemical compound remaining after the glycosyl group on a glycoside is replaced by a hydrogen atom. For example, the aglycone of a cardiac glycoside would be a steroid molecule.
The Joint Committee on Atomic and Molecular Physical Data (JCAMP) defined several JCAMP-DX file formats in chemistry. IUPAC took over the responsibility of maintaining and extending the JCAMP-DX standards from JCAMP in 1995.
In a chemical analysis, the internal standard method involves adding the same amount of a chemical substance to each sample and calibration solution. The internal standard responds proportionally to changes in the analyte and provides a similar, but not identical, measurement signal. It must also be absent from the sample matrix to ensure there is no other source of the internal standard present. Taking the ratio of analyte signal to internal standard signal and plotting it against the analyte concentrations in the calibration solutions will result in a calibration curve. The calibration curve can then be used to calculate the analyte concentration in an unknown sample.
A mass chromatogram is a representation of mass spectrometry data as a chromatogram, where the x-axis represents time and the y-axis represents signal intensity. The source data contains mass information; however, it is not graphically represented in a mass chromatogram in favor of visualizing signal intensity versus time. The most common use of this data representation is when mass spectrometry is used in conjunction with some form of chromatography, such as in liquid chromatography–mass spectrometry or gas chromatography–mass spectrometry. In this case, the x-axis represents retention time, analogous to any other chromatogram. The y-axis represents signal intensity or relative signal intensity. There are many different types of metrics that this intensity may represent, depending on what information is extracted from each mass spectrum.
Alpha-cleavage (α-cleavage) in organic chemistry refers to the act of breaking the carbon-carbon bond adjacent to the carbon bearing a specified functional group.
Vibrational circular dichroism (VCD) is a spectroscopic technique which detects differences in attenuation of left and right circularly polarized light passing through a sample. It is the extension of circular dichroism spectroscopy into the infrared and near infrared ranges.
Transmission Raman spectroscopy (TRS) is a variant of Raman spectroscopy which is advantageous in probing bulk content of diffusely scattering samples. Although it was demonstrated in the early days of Raman spectroscopy it was not exploited in practical settings until much later, probably due to limitations of technology at the time. It was rediscovered in 2006, where the authors showed that it was capable of allowing Raman spectroscopy through many millimetres of tabletted or powdered samples. In addition, this research has also identified several highly beneficial analytical properties of this approach, including the ability to probe bulk content of powders and tissue in the absence of subsampling and to reject Raman and fluorescence components originating from the surface of the sample.
In mass spectrometry, resolution is a measure of the ability to distinguish two peaks of slightly different mass-to-charge ratios ΔM, in a mass spectrum.
In statistics, the bootstrap error-adjusted single-sample technique is a non-parametric method that is intended to allow an assessment to be made of the validity of a single sample. It is based on estimating a probability distribution representing what can be expected from valid samples. This is done use a statistical method called bootstrapping, applied to previous samples that are known to be valid.
Spectral line shape or spectral line profile describes the form of an electromagnetic spectrum in the vicinity of a spectral line – a region of stronger or weaker intensity in the spectrum. Ideal line shapes include Lorentzian, Gaussian and Voigt functions, whose parameters are the line position, maximum height and half-width. Actual line shapes are determined principally by Doppler, collision and proximity broadening. For each system the half-width of the shape function varies with temperature, pressure and phase. A knowledge of shape function is needed for spectroscopic curve fitting and deconvolution.
References
- ↑ McDonald, Robert S.; Wilks, Paul A. (January 1988). "JCAMP-DX: A Standard Form for Exchange of Infrared Spectra in Computer Readable Form" (PDF). Applied Spectroscopy. 42 (1): 151–162. Bibcode:1988ApSpe..42..151M. doi:10.1366/0003702884428734. S2CID 97461751.
- ↑ Davies, Antony N.; Lampen, Peter (August 1993). "JCAMP-DX for NMR" (PDF). Applied Spectroscopy. 47 (8): 1093–1099. Bibcode:1993ApSpe..47.1093D. doi:10.1366/0003702934067874. S2CID 95829936.
- ↑ Lampen, Peter; Hillig, Heinrich; Davies, Antony N.; Linscheid, Michael (December 1994). "JCAMP-DX for Mass Spectrometry" (PDF). Applied Spectroscopy. 48 (12): 1545–1552. Bibcode:1994ApSpe..48.1545L. doi:10.1366/0003702944027840. S2CID 96773027.
- ↑ Baumbach, Jörg Ingo; Davies, Antony N.; Lampen, Peter; Schmidt, Hartwig (2001). "JCAMP-DX. A Standard Format for the Exchange of Ion Mobility Spectrometry Data: (IUPAC Recommendations 2001)" (PDF). Pure and Applied Chemistry. 73. doi:10.1515/iupac.73.0843.
- ↑ Woollett, Benjamin; Klose, Daniel; Cammack, Richard; Janes, Robert W.; Wallace, B. A. (3 October 2012). "JCAMP-DX for circular dichroism spectra and metadata (IUPAC Recommendations 2012)". Pure and Applied Chemistry. 84 (10): 2171–2182. doi: 10.1351/PAC-REC-12-02-03 . S2CID 98027191.
- ↑ Lampen, Peter; Lambert, Jörg; Lancashire, R. J.; McDonald, R. S.; McIntyre, P. S.; Rutledge, D. N.; Fröhlich, Thorsten; Davies, Antony N. (30 August 1999). "An Extension to the JCAMP-DX Standard File Format, JCAMP-DX V.5.01". Pure and Applied Chemistry. 71 (8): 1549–1556. doi: 10.1351/pac199971081549 . S2CID 61246579.
- ↑ Davies, A. N.; Hillig, H.; Linscheid, M. (1990). "JCAMP — DX, A Standard?". Software Development in Chemistry 4. pp. 147–156. doi:10.1007/978-3-642-75430-2_17. ISBN 978-3-540-52173-0.
- ↑ Lancashire, Robert J (December 2007). "The JSpecView Project: an Open Source Java viewer and converter for JCAMP-DX, and XML spectral data files". Chemistry Central Journal. 1 (1): 31. doi: 10.1186/1752-153X-1-31 . PMC 2203984 . PMID 18067663.