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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.
Laser-induced breakdown spectroscopy (LIBS) is a type of atomic emission spectroscopy which uses a highly energetic laser pulse as the excitation source. The laser is focused to form a plasma, which atomizes and excites samples. The formation of the plasma only begins when the focused laser achieves a certain threshold for optical breakdown, which generally depends on the environment and the target material.
Bismuth (83Bi) has 41 known isotopes, ranging from 184Bi to 224Bi. Bismuth has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic weight can be given as 208.98040(1). Although bismuth-209 is now known to be radioactive, it has classically been considered to be a stable isotope because it has a half-life of approximately 2.01×1019 years, which is more than a billion times the age of the universe. Besides 209Bi, the most stable bismuth radioisotopes are 210mBi with a half-life of 3.04 million years, 208Bi with a half-life of 368,000 years and 207Bi, with a half-life of 32.9 years, none of which occurs in nature. All other isotopes have half-lives under 1 year, most under a day. Of naturally occurring radioisotopes, the most stable is radiogenic 210Bi with a half-life of 5.012 days. 210mBi is unusual for being a nuclear isomer with a half-life multiple orders of magnitude longer than that of the ground state.
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Fellgett's advantage or the multiplex advantage is an improvement in signal-to-noise ratio (SNR) that is gained when taking multiplexed measurements rather than direct measurements. The name is derived from P. B. Fellgett, who first made the observation as part of his PhD. When measuring a signal whose noise is dominated by detector noise, a multiplexed measurement such as the signal generated by a Fourier transform spectrometer can produce a relative improvement in SNR, compared to an equivalent scanning monochromator, of the order of the square root of m, where m is the number of sample points comprising the spectrum.
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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.
Two dimensional correlation analysis is a mathematical technique that is used to study changes in measured signals. As mostly spectroscopic signals are discussed, sometime also two dimensional correlation spectroscopy is used and refers to the same technique.
Spectral line shape describes the form of a feature, observed in spectroscopy, corresponding to an energy change in an atom, molecule or ion. This shape is also referred to as the spectral line profile. 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.