Raman methanol

H. Nakamura, and I. Obata. Bus-seiron Kenkyu No. 85, 36-48 (1955). Raman methanol and its aqueous solutions. 

Several properties of the filler are important to the compounder (279). Properties that are frequentiy reported by fumed sihca manufacturers include the acidity of the filler, nitrogen adsorption, oil absorption, and particle size distribution (280,281). The adsorption techniques provide a measure of the surface area of the filler, whereas oil absorption is an indication of the stmcture of the filler (282). Measurement of the sdanol concentration is critical, and some techniques that are commonly used in the industry to estimate this parameter are the methyl red absorption and methanol wettabihty (273,274,277) tests. Other techniques include various spectroscopies, such as diffuse reflectance infrared spectroscopy (drift), inverse gas chromatography (igc), photoacoustic ir, nmr, Raman, and surface forces apparatus (277,283—290). 

Figure 3.6. Resonance Raman spectra of the ground state of DMABN, DMABN- N, DMABN-A, DMABN-A obtained with 330nm excitation in methanol.

Figure 3.14. Picosecond Kerr gated time-resolved resonance Raman (ps-K-TR ) spectra of the ICT state of DMABN (a), DMABN-N (b) and DMABN-dg (c) obtained by 267 nm pnmp, 330nm probe in methanol at 50ps delay time. (Reprinted with permission from reference [28]. Copyright (2001) American Chemical Society.)...

Upon dilution in solvents which may associate via hydrogen bonds (water, methanol, dioxane) the situation is more complex. I.R. and Raman spectroscopy indicate the formation of various monomer-solvent complexes (4, 6). The corresponding absorption bands are in the same range as the characteristic bands for open dimers and oligomers and the latter cannot therefore be determined quantitatively. However, the viscosity of carboxylic acids was found to rise upon addition of water or methanol (4, 7) suggesting that these solvents bind together "oligomers". The persis-... 

For organic hydrogen bonds, methanol takes the role that HF has for inorganic hydrogen bonds it is the simplest conceivable prototype. Its cluster spectroscopy has been reviewed together with that of water clusters [98], While the monomer vibrational dynamics is in general well-studied [214 217], different values for the fundamental O—H stretching band center are in use [63, 64, 75, 173, 189, 218]. Based on combined Raman and IR evidence, a value of 3684 3686 cm 1 appears well-justified [16, 65, 77, 82, 216]. It serves as an important reference for vibrational red shifts in methanol clusters. 

Figure 6. The complex OH stretching spectrum of methanol trimer (bottom) can be explained by sum (v5), difference (vD), and hot bands (vH) involving the OH fundamental (vF) and two umbrella modes of the methyl groups, which are nearly degenerate in the ground state but soften and split after OH stretching excitation. vR is the predominantly Raman active concerted stretching mode [16].

Infrared, Raman, microwave, and double resonance techniques turn out to offer nicely complementary tools, which usually can and have to be complemented by quantum chemical calculations. In both experiment and theory, progress over the last 10 years has been enormous. The relationship between theory and experiment is symbiotic, as the elementary systems represent benchmarks for rigorous quantum treatments of clear-cut observables. Even the simplest cases such as methanol dimer still present challenges, which can only be met by high-level electron correlation and nuclear motion approaches in many dimensions. On the experimental side, infrared spectroscopy is most powerful for the O—H stretching dynamics, whereas double resonance techniques offer selectivity and Raman scattering profits from other selection rules. A few challenges for accurate theoretical treatments in this field are listed in Table I. 

R. Wugt Larsen, P. Zielke, and M. A. Suhm. Hydrogen bonded OH stretching modes of methanol clusters A combined IR and Raman isotopomer study. J. Chem. Phys. 126, 194307 (2007). 

Y. Matsuda, M. Hachiya, A. Fujii, and N. Mikami, Stimulated Raman spectroscopy combined with vacuum ultraviolet photoionization Application to jet cooled methanol clusters as a new vibrational spectroscopic method for size selected species in the gas phase. Chem. Phys. Lett. 442, 217 219 (2007). 

I. Florian, I. Leszczynski, B. G. lohnson, and L. Goodman, Coupled cluster and density functional calculations of the molecular structure, infrared spectra, Raman spectra, and harmonic force constants for methanol. Mol. Phys. 91, 439 447 (1977). 

Time-resolved resonance Raman spectroscopy has been used to study the photorearrangement of o-nitrobenzyl esters in polar and protic solvents53 in acetonitrile, the only primary photoproduct is nitronic acid 68 with a lifetime of 80 microsecond, while in methanol the nitronic acid exists in equilibrium with the nitronate anion 69, giving a lifetime of 100 microseconds (equation 41). 

The use of surface-enhanced resonance Raman spectroscopy (SERRS) as an identification tool in TLC and HPLC has been investigated in detail. The chemical structures and common names of anionic dyes employed as model compounds are depicted in Fig. 3.88. RP-HPLC separations were performed in an ODS column (100 X 3 mm i.d. particla size 5 pm). The flow rate was 0.7 ml/min and dyes were detected at 500 nm. A heated nitrogen flow (200°C, 3 bar) was employed for spraying the effluent and for evaporating the solvent. Silica and alumina TLC plates were applied as deposition substrates they were moved at a speed of 2 mm/min. Solvents A and B were ammonium acetate-acetic acid buffer (pH = 4.7) containing 25 mM tributylammonium nitrate (TBAN03) and methanol, respectively. The baseline separation of anionic dyes is illustrated in Fig. 3.89. It was established that the limits of identification of the deposited dyes were 10 - 20 ng corresponding to the injected concentrations of 5 - 10 /ig/ml. It was further stated that the combined HPLC-(TLC)-SERRS technique makes possible the safe identification of anionic dyes [150],... 

The hydration state of risedronate sodium was monitored continuously in a fluidized bed dryer and correlated to data on the physical stability of tablets made from the monitored material [275]. The final granulation moisture was found to affect the solid-state form, which in turn dictated the drug s physical stability over time. The process of freeze-drying mannitol was monitored continuously with in-line Raman and at-line NIR spectroscopies [276]. The thin polymer solvent coatings, such as poly(vinyl acetate) with toluene, methanol, benzene, and combinations of the solvents, were monitored as they dried to generate concentra-tion/time profiles [277]. 

Fig. 8 (a) DRIFTS spectra of catalyst surface in NO flow. Absorbance increases with time, (b) In situ Raman spectra measured while methanol flowing over catalyst. ... 

The above discussion demonsi rates that it is possible to molecularly design supported metal oxide catalysts with knowledge of the surface oxide - support interactions made possible by the assistance of characterization methods such as Raman spectroscopy and the methanol oxidation reaction. The formation and location of the surface metal oxide species are controlled by the... 

The cyclic molecule Sg is maintained. This is the more usual case and it is observed in various solvents DMSO (dimethyl sulfoxide), DMF (dimethyl formamide), CS2, methanol, and so on, [2, 11, 12]. In this review, we shall denote them as classical solvents. The solutions of sulfur in these solvents are almost uncolored, sKghtly yellow, and absorbing in the UV range. A strong coloration of these solutions would indicate the presence of impurities (e.g. amines) in the solvent. The best evidence that the Sg molecule is kept intact in these solutions is provided by Raman spectroscopy [13, 14]. It must be noted that the rate of dissolution is rather slow the equilibrium is reached, at room temperature, after about one day. 

The oxidation rate of methanol in SCW and the subsequent production and destruction of the primary intermediate, formaldehyde, has been investigated using Raman spectroscopy as an in situ analytical method. Effluent samples were also examined using gas chromatography. An elementary reaction mechanism, which reproduces accurately the quantitative features of methanol oxidation and formaldehyde production, is used to identify key rate controlling reactions during the induction period and the transition to the primary oxidation path (Rice et al., 1996). 

TPRS experiments for this reaction step. The two hydrogens released in the methanol adsorption and the surface methoxy decomposition steps are eventually converted to water. Spectroscopic details about the formation of water are presently not available, but the formation of water most likely proceeds via the condensation of two surface hydroxyl groups. The reduced surface vanadia site is readily reoxidized back to vanadium (+5) by gas phase oxygen as shown by in situ Raman measurements.42... 

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