Raman water peak

Fluorescence is an extremely sensitive technique but it is not suitable as a general method to estimate natural DOC content due to the reason that it is impossible to find a reference material that would be common for all different natural waters. Characteristic for different fluorescence studies of NOM/DOM is that they may occasionally be somewhat surprising, contradictory, or laboriously explicable. The main reason for this incoherence is that fluorescence measurements are affected by many environmental factors, e.g., type of solution, pH, ionic strength, temperature, redox potential of the medium, and interactions with metal ions and organics. Several corrections are required to obtain a reliable and comparable spectrum, e.g., instrumental factors, Raman water peak, scattering effects (primary and secondary inner filter effects [31,32]), arbitrary fluorescence units should be standardized (dihydrate of quinine sulfate), etc. 

A test for the sensitivity of a fluorimeter is to measure the intensity of fluorescence of the Raman diffusion peak of a cell filled with water and with an optical pathlength of 1 cm. If the wavelength of excitation is regulated to 250 nm, at which wavelength must the measurement be made (the Raman displacement of water is 3 380 cm-1) ... 

Among the basic amino acids, SERS of histidine has been studied on a roughened Cu electrode [255] in water and D2O solutions. Depending on the pH of the solution histidine exists in five different ionic forms Eq. (6.7), which can be distinguished by the shift in Raman/SERS peak positions as studied by Martusevicius et al. [255] ... 

Figure 7. CDOM fluorescence of water from two lakes (Hargreaves, unpublished) emission scans for excitation at 370 nm (Shimadzu 551 fluorometer), before and after subtraction of water blank. Samples deionized water (DIW), L. Giles water (ca. 1 g m DOC), L. Lacawac water (ca. 5 g m DOC) The Raman scattering peak at 417 nm represents a shift in wavenumber by 3400 cm from the excitation wavenumber. The broad peak is contributed predominantly by the fulvic acid fraction of DOM. The peak wavelength and fluorescence index ratio for these samples (L. Giles, 452 nm peak and ratio = 1.5 L. Lacawac, 455 mn peak and ratio = 1.4) suggest a slight difference in CDOM...

Time-domain THz measurement for molecular mobility studies Raman signals are less affected by water peaks but confronted by fluorescence related artifacts from elastic scattering... 

Lawaetz, A. and Stedmon, C. (2009). Huorescence intensity calibration using the Raman scatter peak of water. Appl. Spectrosc., 63(8), 936-940. 

The state of aqueous solutions of nitric acid In strongly acidic solutions water is a weaker base than its behaviour in dilute solutions would predict, for it is almost unprotonated in concentrated nitric acid, and only partially protonated in concentrated sulphuric acid. The addition of water to nitric acid affects the equilibrium leading to the formation of the nitronium and nitrate ions ( 2.2.1). The intensity of the peak in the Raman spectrum associated with the nitronium ion decreases with the progressive addition of water, and the peak is absent from the spectrum of solutions containing more than about 5% of water a similar effect has been observed in the infra-red spectrum. ... 

Bolis et al (43) reported volumetric data characterizing NH3 adsorption on TS-1 that demonstrate that the number of NH3 molecules adsorbed per Ti atom under saturation conditions was close to two, suggesting that virtually all Ti atoms are involved in the adsorption and have completed a 6-fold coordination Ti(NH3)204. The reduction of the tetrahedral symmetry of Ti4+ ions in the silicalite framework upon adsorption of NH3 or H20 is also documented by a blue shift of the Ti-sensitive stretching band at 960 cm-1 (43,45,134), by a decrease of the intensity of the XANES pre-edge peak at 4967 eV (41,43,134), and by the extinction of the resonance Raman enhancement of the 1125 cm-1 band in UV-Raman spectra (39,41). As an example, spectra in Figs. 15 and 16 show the effect of adsorbed water on the UV-visible (Fig. 15), XANES (Fig. 16a), and UV-Raman (Fig. 16b) spectra of TS-1. 

The IR spectmm of water at room temperature and one atmosphere pressure [61 63] is peaked at about 3400 cm 1 and has a weak shoulder at about 3250 cm 1 and a FWHM of about 375cm 1. Raman spectra are quite different [49, 64 70] The VV spectmm is bimodal, with strong peaks at about 3400 and 3250 cm 1, and an FWHM of about 425 cm 1, while the VH spectmm peaks at about 3460 cm l, is quite asymmetric, and has a FWHM of about 300 cm 1. Note that the gas-phase water molecule has symmetric and antisymmetric stretch fundamentals (both of which are IR and Raman active) at 3657 and 3756 cm 1, respectively, and so the liquid-state spectra are significantly red-shifted from these values furthermore, the breadths of the liquid-state spectra are substantially larger than this gas-phase splitting. 

Raman scattering in water is used as a sensitivity test for fluorimeters. The test consists of measuring the signal to noise ratio of the Raman peak using a cell filled with water. For example, signal/noise will be measured at 397 nm (25191 cm1) if the excitation energy used is 350 nm (28571 cm 1). 

When an electron is injected into a polar solvent such as water or alcohols, the electron is solvated and forms so-called the solvated electron. This solvated electron is considered the most basic anionic species in solutions and it has been extensively studied by variety of experimental and theoretical methods. Especially, the solvated electron in water (the hydrated electron) has been attracting much interest in wide fields because of its fundamental importance. It is well-known that the solvated electron in water exhibits a very broad absorption band peaked around 720 nm. This broad absorption is mainly attributed to the s- p transition of the electron in a solvent cavity. Recently, we measured picosecond time-resolved Raman scattering from water under the resonance condition with the s- p transition of the solvated electron, and found that strong transient Raman bands appeared in accordance with the generation of the solvated electron [1]. It was concluded that the observed transient Raman scattering was due to the water molecules that directly interact with the electron in the first solvation shell. Similar results were also obtained by a nanosecond Raman study [2]. This finding implies that we are now able to study the solvated electron by using vibrational spectroscopy. In this paper, we describe new information about the ultrafast dynamics of the solvated electron in water, which are obtained by time-resolved resonance Raman spectroscopy. 

A further low-intensity peak, known as the Raman band, is also observed in spectra (see Fig. B3.6.1). This is a low-intensity band of scattered radiation whose distance from the excitation band is a measure of the vibrational energy of the H-0 bond in solvent water. At A,ex = 280 nm, the Raman band for water occurs at 311 nm in general, it occurs at l/ (1/X.ex) - (3.6 x 10-4), where A,ex is the excitation wavelength in nm. The intensity and resolution of the Raman band provide a useful empirical check on the performance of the spectrofluorometer. A decrease in the signal-to-noise ratio usually indicates a deterioration of the lamp. 

Chamberlain and co-workers (17) have noted that no distinct peak occurs in the infrared absorption spectrum of water below 193 cm.-1. The Raman scattering does give rise to a peak near 60 cm."1 while slow neutron scattering give rise to a number of peaks, including a notable one at 56 cm.-1. This discrepancy implies that a significant number of low frequency oscillations may exist in liquid water with little if any infrared activity. 

Raman measurements and solubility predictions of the guest molecule concentration within the bulk aqueous phase suggest that the hydrate film thickens into the water phase (Makogon et al., 1998 Subramanian and Sloan, 2000 Subramanian, 2000). The Raman peak area for methane (C-H... 

The trends shown from the predicted curves, Csh and Cs, are in qualitative agreement with corresponding dissolved methane Raman peak intensities. Therefore, the Raman spectra (Figure 3.27a) support the proposed mechanism that hydrate growth occurs in part as a result of methane diffusing from the bulk aqueous phase to the hydrate film formed at the vapor-liquid interface. This decreases the methane concentration in the bulk water phase. Hydrate growth from an aqueous... 

Figure 3.27 Methane hydrate film development at the water-methane interface from dissolved methane in the aqueous phase, as indicated from Raman spectroscopy (a) and methane solubility predictions (b). (a) A series of Raman spectra of dissolved methane collected at different temperatures during the continuous cooling process. Spectra marked A through E correspond to temperatures of 24°C, 20°C, 15.6°C, 10.2°C, and 2.8°C, respectively. (b) A schematic illustration of temperature dependencies of the equilibrium methane concentration in liquid water (C = without hydrate, Qjh = with hydrate). The scale of the vertical axis is arbitrary, but the Raman peak area is proportional to methane dissolved in water. Points A through F correspond to different temperatures during the continuous cooling process. (From Subramanian, S., Measurements ofClathrate Hydrates Containing Methane and Ethane Using Raman Spectroscopy, Ph.D. Thesis, Colorado School of Mines, Golden, CO (2000). With permission.)...

---