Inorganic Chemistry (journal)
Inorganic Chemistry is a biweekly peer-reviewed scientific journal published by the American Chemical Society since 1962. It covers research in all areas of inorganic chemistry. Inorganic Chemistry is abstracted and indexed in Chemical Abstracts Service, Scopus, EBSCOhost, Thomson-Gale, ProQuest, PubMed, Web of Science, SwetsWise; the current editor-in-chief is William B. Tolman
Spectroscopy is the study of the interaction between matter and electromagnetic radiation. Spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism; the concept was expanded to include any interaction with radiative energy as a function of its wavelength or frequency, predominantly in the electromagnetic spectrum, though matter waves and acoustic waves can be considered forms of radiative energy. Spectroscopic data are represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. Spectroscopy in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of physics and astronomy, allowing the composition, physical structure and electronic structure of matter to be investigated at atomic scale, molecular scale, macro scale, over astronomical distances. Important applications arise from biomedical spectroscopy in the areas of tissue analysis and medical imaging. Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are used to describe experimental spectroscopic methods.
Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers. Daily observations of color can be related to spectroscopy. Neon lighting is a direct application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies. Neon lamps use collision of electrons with the gas to excite these emissions. Inks and paints include chemical compounds selected for their spectral characteristics in order to generate specific colors and hues. A encountered molecular spectrum is that of nitrogen dioxide. Gaseous nitrogen dioxide has a characteristic red absorption feature, this gives air polluted with nitrogen dioxide a reddish-brown color. Rayleigh scattering is a spectroscopic scattering phenomenon. Spectroscopic studies were central to the development of quantum mechanics and included Max Planck's explanation of blackbody radiation, Albert Einstein's explanation of the photoelectric effect and Niels Bohr's explanation of atomic structure and spectra.
Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect and quantify information about the atoms and molecules. Spectroscopy is used in astronomy and remote sensing on Earth. Most research telescopes have spectrographs; the measured spectra are used to determine the chemical composition and physical properties of astronomical objects. One of the central concepts in spectroscopy is its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency. This plot is one type of spectrum, with the peak referred to as a spectral line, most spectral lines have a similar appearance. In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon.
The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy of a photon is related to its frequency by E = h ν where h is Planck's constant, so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can excite resonant interactions. Spectra of atoms and molecules consist of a series of spectral lines, each one representing a resonance between two different quantum states; the explanation of these series, the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first explained by the Rutherford-Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can overlap and appear to be a single transition if the density of energy states is high enough.
Named series of lines include the principal, sharp and fundamental series. Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques; the various implementations and techniques can be classified in several ways. The types of spectroscopy are distinguished by the type of radiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy; the types of radiative energy studied include: Electromagnetic radiation was the first source of energy used for spectroscopic studies. Techniques that employ electromagnetic radiation are classified by the wavelength region of the spectrum and include microwave, terahe
Bisulfite sequencing is the use of bisulfite treatment of DNA before routine sequencing to determine the pattern of methylation. DNA methylation was the first discovered epigenetic mark, remains the most studied. In animals it predominantly involves the addition of a methyl group to the carbon-5 position of cytosine residues of the dinucleotide CpG, is implicated in repression of transcriptional activity. Treatment of DNA with bisulfite converts cytosine residues to uracil, but leaves 5-methylcytosine residues unaffected. Therefore, DNA, treated with bisulfite retains only methylated cytosines. Thus, bisulfite treatment introduces specific changes in the DNA sequence that depend on the methylation status of individual cytosine residues, yielding single-nucleotide resolution information about the methylation status of a segment of DNA. Various analyses can be performed on the altered sequence to retrieve this information; the objective of this analysis is therefore reduced to differentiating between single nucleotide polymorphisms resulting from bisulfite conversion.
Bisulfite sequencing applies routine sequencing methods on bisulfite-treated genomic DNA to determine methylation status at CpG dinucleotides. Other non-sequencing strategies are employed to interrogate the methylation at specific loci or at a genome-wide level. All strategies assume that bisulfite-induced conversion of unmethylated cytosines to uracil is complete, this serves as the basis of all subsequent techniques. Ideally, the method used would determine the methylation status separately for each allele. Alternative methods to bisulfite sequencing include Combined Bisulphite Restriction Analysis and methylated DNA immunoprecipitation. Methodologies to analyze bisulfite-treated DNA are continuously being developed. To summarize these evolving methodologies, numerous review articles have been written; the methodologies can be divided into strategies based on methylation-specific PCR, strategies employing polymerase chain reaction performed under non-methylation-specific conditions. Microarray-based methods use PCR based on non-methylation-specific conditions also.
The first reported method of methylation analysis using bisulfite-treated DNA utilized PCR and standard dideoxynucleotide DNA sequencing to directly determine the nucleotides resistant to bisulfite conversion. Primers are designed to be strand-specific as well as bisulfite-specific, flanking the methylation site of interest. Therefore, it will amplify both methylated and unmethylated sequences, in contrast to methylation-specific PCR. All sites of unmethylated cytosines are displayed as thymines in the resulting amplified sequence of the sense strand, as adenines in the amplified antisense strand. By incorporating high throughput sequencing adaptors into the PCR primers, PCR products can be sequenced with massively parallel sequencing. Alternatively, labour-intensively, PCR product can be cloned and sequenced. Nested PCR methods can be used to enhance the product for sequencing. All subsequent DNA methylation analysis techniques using bisulfite-treated DNA is based on this report by Frommer et al..
Although most other modalities are not true sequencing-based techniques, the term "bisulfite sequencing" is used to describe bisulfite-conversion DNA methylation analysis techniques in general. Pyrosequencing has been used to analyze bisulfite-treated DNA without using methylation-specific PCR. Following PCR amplification of the region of interest, pyrosequencing is used to determine the bisulfite-converted sequence of specific CpG sites in the region; the ratio of C-to-T at individual sites can be determined quantitatively based on the amount of C and T incorporation during the sequence extension. The main limitation of this method is the cost of the technology. However, Pyrosequencing does well allow for extension to high-throughput screening methods. A further improvement to this technique was described by Wong et al. which uses allele-specific primers that incorporate single-nucleotide polymorphisms into the sequence of the sequencing primer, thus allowing for separate analysis of maternal and paternal alleles.
This technique is of particular usefulness for genomic imprinting analysis. This method is based on the single-strand conformation polymorphism analysis method developed for single-nucleotide polymorphism analysis. SSCA differentiates between single-stranded DNA fragments of identical size but distinct sequence based on differential migration in non-denaturating electrophoresis. In MS-SSCA, this is used to distinguish between bisulfite-treated, PCR-amplified regions containing the CpG sites of interest. Although SSCA lacks sensitivity when only a single nucleotide difference is present, bisulfite treatment makes a number of C-to-T conversions in most regions of interest, the resulting sensitivity approaches 100%. MS-SSCA provides semi-quantitative analysis of the degree of DNA methylation based on the ratio of band intensities. However, this method is designed to assess all CpG sites as a whole in the region of interest rather than individual methylation sites. A further method to differentiate converted from unconverted bisulfite-treated DNA is using high-resolution melting analysis, a quantitative PCR-based technique designed to distinguish SNPs.
The PCR amplicons are analyzed directly by temperature ramping and resulting liberation of an intercalating fluorescent dye during melting. The degree of methylation, as represented by the C-to-T content in th
Acid dissociation constant
An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid–base reactions. K a =; the chemical species HA, A−, H+ are said to be in equilibrium when their concentrations do not change with the passing of time, because both forward and backward reactions are occurring at the same fast rate. The chemical equation for acid dissociation can be written symbolically as: HA ↽ − − ⇀ A − + H + where HA is a generic acid that dissociates into A−, the conjugate base of the acid and a hydrogen ion, H+, it is implicit in this definition that the quotient of activity coefficients, Γ, Γ = γ A − γ H + γ A H is a constant that can be ignored in a given set of experimental conditions. For many practical purposes it is more convenient to discuss the logarithmic constant, pKa p K a = − log 10 The more positive the value of pKa, the smaller the extent of dissociation at any given pH —that is, the weaker the acid.
A weak acid has a pKa value in the approximate range −2 to 12 in water. For a buffer solution consisting of a weak acid and its conjugate base, pKa can be expressed as: p K a = pH − log 10 The pKa for a weak monoprotic acid is conveniently determined by potentiometric titration with a strong base to the equivalence point and taking the pH value measured at one-half this volume as being equal to pKa; that is because at this half equivalence point, the number of moles of strong base added is one-half the number of moles of weak acid present, while the concentrations of the conjugate base and the remaining weak acid are the same. Acids with a pKa value of less than about −2 are said to be strong acids. In water, the dissociation of a strong acid in dilute solutions is complete such that the final concentration of the undissociated acid final is low. Consider a strong monoprotic acid, such as HCl; because of their 1:1 ratio, the final concentration of the conjugate base, final, is taken to be equal to the concentration of the hydronium ion, which can be directly measured by a pH meter.
For strong monoprotic acids like HCl, final and are both nearly equal to the initial concentration of initial placed into solution. With conventional acid-base titration methods it is difficult to measure the pH of a strong acid solution and, hence, to determine the or final, with a sufficient number of significant figures to and compute the low values encountered for final, which can be as low as 10-9 mol per liter for some strong acids. Furthermore, if 100% dissociation is assumed, final is zero and the fraction within parenthesis in the equation above becomes undefined; because the second expression on the right-hand side of the above equation is therefore indeterminable by conventional titration methods, the entire equation is not as useful a means of experimentally measuring pKa for strong acids as it is for weak acids. However, pKa and/or Ka values for strong acids can be estimated by theoretical means, such as computing gas phase dissociation constants and using Gibbs free energies of solvation for the molecular anions.
It is possible to use spectroscopy in some cases to determine the ratio of the concentrations of the conjugate base produced and the undissociated acid. For example, the Raman spectra of dilute nitric acid solutions contain signals of the nitrate ion and as the solutions become more concentrated signals of undissociated nitric acid molecules emerge; the acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction. The value of the pKa changes with temperature and can be understood qualitatively based on Le Châtelier's principle: when the reaction is endothermic, Ka increases and pKa decreases with
Sodium bisulfite is a chemical compound with the chemical formula NaHSO3. Sodium bisulfite is a food additive with E number E222; this salt of bisulfite can be prepared by bubbling sulfur dioxide in a solution of sodium carbonate in water. Sodium bisulfite in contact with chlorine bleach will generate heat and form sodium bisulfate and sodium chloride. Sodium bisulfite can be prepared by bubbling excess sulfur dioxide through a solution of suitable base, such as sodium hydroxide or sodium bicarbonate. SO2 + NaOH → NaHSO3 SO2 + NaHCO3 → NaHSO3 + CO2 Sodium bisulfite is a weakly acidic species with a pKa of 6.97. Its conjugate base is the sulfite ion, SO32−: HSO3− ↔ SO32− + H+The theoretical protonated species is sulfurous acid, it forms a bisulfite adduct with aldehyde groups and with certain cyclic ketones to give a sulfonic acid. This reaction is useful for purification procedures. Contaminated aldehydes in a solution precipitate as the bisulfite adduct which can be isolated by filtration; the reverse reaction takes place in presence of a base such as sodium bicarbonate or sodium hydroxide and the bisulfite is liberated as sulfur dioxide.
Examples of such procedures are described for benzaldehyde, 2-tetralone, the ethyl ester of pyruvic acid and glyoxal. In the ring-expansion reaction of cyclohexanone with diazald, the bisulfite reaction is reported to be able to differentiate between the primary reaction product cycloheptanone and the main contaminant cyclooctanone; the other main use of sodium bisulfite is as a mild reducing agent in organic synthesis in particular in purification procedures. It can efficiently remove traces or excess amounts of chlorine, iodine, hypochlorite salts, osmate esters, chromium trioxide and potassium permanganate. A third use of sodium bisulfite is as a decoloration agent in purification procedures because it can reduce coloured oxidizing agents, conjugated alkenes and carbonyl compounds. Sodium bisulfite is the key ingredient in the Bucherer reaction. In this reaction an aromatic hydroxyl group is replaced by an aromatic amine group and vice versa because it is a reversible reaction; the first step in this reaction is an addition reaction of sodium bisulfite to an aromatic double bond.
The Bucherer carbazole synthesis is a related organic reaction that uses sodium bisulfite as a reagent. While the related compound, sodium metabisulfite, is used in all commercial wines to prevent oxidation and preserve flavor, sodium bisulfite is sold by some home winemaking suppliers for the same purpose. In fruit canning, sodium bisulfite is used to kill microbes. In the case of wine making, sodium bisulfite releases sulfur dioxide gas when added to water or products containing water; the sulfur dioxide kills yeasts and bacteria in the grape juice before fermentation. When the sulfur dioxide levels have subsided, fresh yeast is added for fermentation, it is added to bottled wine to prevent the formation of vinegar if bacteria are present, to protect the color and flavor of the wine from oxidation, which causes browning and other chemical changes. The sulfur dioxide reacts with oxidation by-products and prevents them from causing further deterioration. Sodium bisulfite is added to leafy green vegetables in salad bars and elsewhere, to preserve apparent freshness, under names like LeafGreen.
The concentration is sometimes high enough to cause allergic reactions. On July 8, 1986, sodium bisulfite was banned from use by the FDA on fresh fruits and vegetables in the United States following the deaths of 13 people and many illnesses among asthmatics. Sodium bisulfite is used in the analysis of the methylation status of cytosines in DNA. In this technique, sodium bisulfite deaminates cytosine into uracil, but does not affect 5-methylcytosine, a methylated form of cytosine with a methyl group attached to carbon 5; when the bisulfite-treated DNA is amplified via polymerase chain reaction, the uracil is amplified as thymine and the methylated cytosines are amplified as cytosine. DNA sequencing techniques are used to read the sequence of the bisulfite-treated DNA; those cytosines that are read as cytosines after sequencing represent methylated cytosines, while those that are read as thymines represent unmethylated cytosines in the genomic DNA. Sodium bisulfite is a common reducing agent in the chemical industry, as it reacts with dissolved oxygen: 2 NaHSO3 + O2 → 2 NaHSO4It is added to large piping systems to prevent oxidative corrosion.
In biochemical engineering applications, it is helpful to maintain anaerobic conditions within a reactor. Sodium bisulfite should not be confused with sodium bisulfate, used as a pH lowering chemical for swimming pools. In drinking water treatment, sodium bisulfite is added after super chlorination, to reduce the residual chlorine before discharging to the service reservoir. In wastewater treatment, sodium bisulfite is added following disinfection with chlorine prior to discharging the effluent to the receiving water. Residual chlorine can have a negative impact on aquatic life. In steam boilers, sodium bisulfite has been a reliable oxygen scavenger in boiler feedwater for 60 years; this compound is characterized as having fast reaction times, low use-cost, years of proven performance, availability. Sodium bisulfite when used in steam boilers has USDA approvals. Sodium metabisul
Sulfonamide is a functional group, the basis of several groups of drugs, which are called sulphonamides, sulfa drugs or sulpha drugs. The original antibacterial sulfonamides are synthetic antimicrobial agents that contain the sulfonamide group; some sulfonamides are devoid of antibacterial activity, e.g. the anticonvulsant sultiame. The sulfonylureas and thiazide diuretics are newer drug groups based upon the antibacterial sulfonamides. Allergies to sulfonamide are common; the overall incidence of adverse drug reactions to sulfa antibiotics is 3%, close to penicillin. It is important to make a distinction between sulfa drugs and other sulfur-containing drugs and additives, such as sulfates and sulfites, which are chemically unrelated to the sulfonamide group, do not cause the same hypersensitivity reactions seen in the sulfonamides. Nowadays, while sulfonamides appear in the prescriptions written by doctors in developed countries, sulfonamides are still common antimicrobial medications in developing countries owing to their low price.
In bacteria, antibacterial sulfonamides act as competitive inhibitors of the enzyme dihydropteroate synthase, an enzyme involved in folate synthesis. Sulfonamides are therefore bacteriostatic and inhibit growth and multiplication of bacteria, but do not kill them. Humans, in contrast to bacteria, acquire folate through the diet. Sulfonamides are used to treat allergies and cough, as well as antifungal and antimalarial functions; the moiety is present in other medications that are not antimicrobials, including thiazide diuretics, loop diuretics, acetazolamide and some COX-2 inhibitors. Sulfasalazine, in addition to its use as an antibiotic, is used in the treatment of inflammatory bowel disease. Sulfonamide drugs were the first antibacterials to be used systemically, paved the way for the antibiotic revolution in medicine; the first sulfonamide, trade-named Prontosil, was a prodrug. Experiments with Prontosil began in 1932 in the laboratories of Bayer AG, at that time a component of the huge German chemical trust IG Farben.
The Bayer team believed that coal-tar dyes which are able to bind preferentially to bacteria and parasites might be used to attack harmful organisms in the body. After years of fruitless trial-and-error work on hundreds of dyes, a team led by physician/researcher Gerhard Domagk found one that worked: a red dye synthesized by Bayer chemist Josef Klarer that had remarkable effects on stopping some bacterial infections in mice; the first official communication about the breakthrough discovery was not published until 1935, more than two years after the drug was patented by Klarer and his research partner Fritz Mietzsch. Prontosil, as Bayer named the new drug, was the first medicine discovered that could treat a range of bacterial infections inside the body, it had a strong protective action against infections caused by streptococci, including blood infections, childbed fever, erysipelas, a lesser effect on infections caused by other cocci. However, it had no effect at all in the test tube, exerting its antibacterial action only in live animals.
It was discovered by Bovet, Federico Nitti and J. and Th. Jacques Tréfouël, a French research team led by Ernest Fourneau at the Pasteur Institute, that the drug was metabolized into two pieces inside the body, releasing from the inactive dye portion a smaller, active compound called sulfanilamide; the discovery helped establish the concept of "bioactivation" and dashed the German corporation's dreams of enormous profit. The result was a sulfa craze. For several years in the late 1930s, hundreds of manufacturers produced tens of thousands of tons of myriad forms of sulfa; this and nonexistent testing requirements led to the elixir sulfanilamide disaster in the fall of 1937, during which at least 100 people were poisoned with diethylene glycol. This led to the passage of the Federal Food and Cosmetic Act in 1938 in the United States; as the first and only effective antibiotic available in the years before penicillin, sulfa drugs continued to thrive through the early years of World War II. They are credited with saving the lives of tens of thousands of patients, including Franklin Delano Roosevelt Jr. and Winston Churchill.
Sulfa had a central role in preventing wound infections during the war. American soldiers were issued a first-aid kit containing sulfa pills and powder, were told to sprinkle it on any open wound; the sulfanilamide compound is more active in the protonated form. The drug has low solubility and sometimes can crystallize in the kidneys, due to its first pKa of around 10; this is a painful experience, so patients are told to take the medication with copious amounts of water. Newer analogous compounds prevent this complication because they have a lower pKa, around 5–6, making them more to remain in a soluble form. Many thousands of molecules containing the sulfanilamide structure have been created since its discovery, yielding improved formulations with greater effectiveness and less toxicity. Sulfa drugs are still used for conditions such as acne and urinary tract in
Raman spectroscopy. Raman spectroscopy is used in chemistry to provide a structural fingerprint by which molecules can be identified, it relies on inelastic scattering, or Raman scattering, of monochromatic light from a laser in the visible, near infrared, or near ultraviolet range. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down; the shift in energy gives information about the vibrational modes in the system. Infrared spectroscopy yields complementary, information. A sample is illuminated with a laser beam. Electromagnetic radiation from the illuminated spot is collected with a lens and sent through a monochromator. Elastic scattered radiation at the wavelength corresponding to the laser line is filtered out by either a notch filter, edge pass filter, or a band pass filter, while the rest of the collected light is dispersed onto a detector. Spontaneous Raman scattering is very weak, as a result the main difficulty of Raman spectroscopy is separating the weak inelastically scattered light from the intense Rayleigh scattered laser light.
Raman spectrometers used holographic gratings and multiple dispersion stages to achieve a high degree of laser rejection. In the past, photomultipliers were the detectors of choice for dispersive Raman setups, which resulted in long acquisition times. However, modern instrumentation universally employs notch or edge filters for laser rejection and spectrographs either axial transmissive, Czerny–Turner monochromator, or FT, CCD detectors; the advanced types of Raman spectroscopy include surface-enhanced Raman, resonance Raman, tip-enhanced Raman, polarized Raman, stimulated Raman, transmission Raman, spatially offset Raman, hyper Raman. The magnitude of the Raman effect correlates with polarizability of the electrons in a molecule, it is a form of inelastic light scattering. This excitation puts the molecule into a virtual energy state for a short time before the photon is emitted. Inelastic scattering means that the energy of the emitted photon is of either lower or higher energy than the incident photon.
After the scattering event, the sample is in a different vibrational state. For the total energy of the system to remain constant after the molecule moves to a new rovibronic state, the scattered photon shifts to a different energy, therefore a different frequency; this energy difference is equal to that between the initial and final rovibronic states of the molecule. If the final state is higher in energy than the initial state, the scattered photon will be shifted to a lower frequency so that the total energy remains the same; this shift in frequency is called downshift. If the final state is lower in energy, the scattered photon will be shifted to a higher frequency, called an anti-Stokes shift, or upshift. For a molecule to exhibit a Raman effect, there must be a change in its electric dipole-electric dipole polarizability with respect to the vibrational coordinate corresponding to the rovibronic state; the intensity of the Raman scattering is proportional to this polarizability change. Therefore, the Raman spectrum depends on the rovibronic states of the molecule.
The Raman effect is based on the interaction between the electron cloud of a sample and the external electric field of the monochromatic light, which can create an induced dipole moment within the molecule based on its polarizability. Because the laser light does not excite the molecule there can be no real transition between energy levels; the Raman effect should not be confused with emission, where a molecule in an excited electronic state emits a photon and returns to the ground electronic state, in many cases to a vibrationally excited state on the ground electronic state potential energy surface. Raman scattering contrasts with infrared absorption, where the energy of the absorbed photon matches the difference in energy between the initial and final rovibronic states; the dependence of Raman on the electric dipole-electric dipole polarizability derivative differs from IR spectroscopy, which depends on the electric dipole moment derivative, the atomic polar tensor. This contrasting feature allows rovibronic transitions that might not be active in IR to be analyzed using Raman spectroscopy, as exemplified by the rule of mutual exclusion in centrosymmetric molecules.
Transitions which have large Raman intensities have weak IR intensities and vice versa. If a bond is polarized, a small change in its length such as that occurs during a vibration, has only a small resultant effect on polarization. Vibrations involving polar bonds are therefore, comparatively weak Raman scatterers; such polarized bonds, carry their electrical charges during the vibrational motion, this results in a larger net dipole moment change during the vibration, producing a strong IR absorption band. Conversely neutral bonds suffer large changes in polarizability during a vibration. However, the dipole moment is not affected such that while vibrations involving predominantly this type of bond are strong Raman scatterers, they are weak in the IR. A third vibrational spectroscopy technique, inelastic incoherent n