Spectroscopy utilization

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

The films were characterized using x-ray powder diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The photoelectron spectroscopy utilized a Vacuum Generators ESCA Lab II system with Mg(Ka) radiation. Binding energies (BE) were measured with respect to the surface C(ls) peak (284.5 eV) which was always present In these films. Scanning electron microscopy was done with a JEOL JSM-35C system. 

STM-Raman spectroscopy utilizes the effect that Raman scattering is enhanced for a molecule in the vicinity of a metal nanostructure. This enhancement effect is generally called surface-enhanced Raman scattering (SERS). When a sharp scanning probe, such as a tunneling tip for STM, is used as a metal nanostructure to enhance Raman intensity, it is called tip-enhanced Raman scattering (TERS). The concept of STM combined with Raman spectroscopy is presented in Figure 1.1. 

CARS spectroscopy utilizes three incident fields including a pump field (coi), a Stokes field (CO2 C02nonlinear polarization at cOcars = 2c0i — CO2. When coi — CO2 coincides with one of the molecular-vibration frequencies of a given sample, the anti-Stokes Raman signal is resonantly generated [22, 23]. We induce the CARS polarization by the tip-enhanced field at the metallic tip end of the nanometric scale. 

Quantitative analysis in flame atomic absorption spectroscopy utilizes Beer s law. The standard curve is a Beer s law plot, a plot of absorbance vs. concentration. The usual procedure, as with other quantitative instrumental methods, is to prepare a series of standard solutions over a concentration range suitable for the samples being analyzed, i.e., such that the expected sample concentrations are within the range established by the standards. The standards and the samples are then aspirated into the flame and the absorbances read from the instrument The Beer s law plot will reveal the useful linear range and the concentrations of the sample solutions. In addition, information on useful linear ranges is often available for individual elements and instrument conditions from manufacturers and other literature. 

The comprehensive dedicated research ultimately made it possible to decode the patterns of labelling in almost any type of tritium labelled compound at low isotopic abundance (e.g., 3 x 10 4 to 3 x 10 2 per cent. 3H per site) with the aid of 3H-NMR directly, rapidly, reliably and non-destructive analytical means. Since, 1971, the 3H-NMR spectroscopy, utilizing only millicurie (mCi) quantities of radioactivity, emerged as a most useful analytical tool for the study of tritium labelled compounds. 

Emission spectroscopy utilizes the characteristic line emission from atoms as their electrons drop from the excited to the ground state. The earliest version of emission spectroscopy as applied to chemistry was the flame test, where samples of elements placed in a Bunsen burner will change the flame to different colors (sodium turns the flame yellow calcium turns it red, copper turns it green). The modem version of emission spectroscopy for the chemistry laboratory is ICP-AES. In this technique rocks are dissolved in acid or vaporized with a laser, and the sample liquid or gas is mixed with argon gas and turned into a plasma (ionized gas) by a radio frequency generator. The excited atoms in the plasma emit characteristic energies that are measured either sequentially with a monochromator and photomultiplier tube, or simultaneously with a polychrometer. The technique can analyze 60 elements in minutes. 

Conventional Raman spectroscopy utilizes rectangular or cylindrical cuvettes. A given spectrometer collects maximum intensity of Raman radiation of a sample, if the sample is placed in the focal region of a laser beam and if a maximum amount of the Raman radiation emerging from this sample is collected by a sample optics of the spectrometer within a maximum solid angle (Schrader, 1980). As mentioned in Sec. 3.1, the optical conductance of the entrance optics should have the same value as that of the interferometer or monochromator. Inspection of conventional sample arrangements shows that these conditions were often not fulfilled optimally ... 

Technical requirements for SERS-based imaging is almost the same as the detection technologies discussed above, but imaging technology rather focuses on visualization of targeted area in cells and tissues. UV-resonance Raman spectroscopy utilizes resonance-enhanced Raman signal from certain chromophores for... 

Powdered samples of CbAsFb, CioAsFb and fluorinated CioAsFs were subjected to X-ray absorption spectroscopy utilizing the high intensity X-ray source available at the Stanford Linear Accelerator Synchrotron Facility. The samples were housed in air tight Teflon-gasketed containers provided with... 

In addition to standard methods of monitoring the reaction progress by UV and visible spectroscopies, other detection methods also can be used. For example, electron-transfer reactions between monomeric and dimeric metal carbonyl complexes in Eq. 11 have been studied by infrared stopped-flow spectroscopy utilizing a tunable CO laser as a source of infrared radiation and a HgCdGe detector [12]. 

Oare earth forms of zeolites X and Y type faujasites possess superior catalytic properties for various reactions such as alkylation, isomerization, and cracking (9, 12, 18). Structural studies involving x-ray diffraction and CO chemisorption have been made to locate the positions of the rare earth (11, 14, 16). Hydroxyl groups and their relationship to surface acidity have been studied by infrared spectroscopy, utilizing the adsorption of pyridine and other basic molecules (2, 6, 21, 22, 23). Since much of the previous research has involved measurements on mixed rare earth faujasites, a need existed for a more systematic study of the individual rare earth zeolites, in regard to both structural and catalytic properties. The present investigation deals with the Y, La, Ce, Pr, Sm,... 

XPS (x-ray photoelectron spectroscopy) utilizes photoionization and energy-disperse analysis of the emitted photoelectrons to study the composition and electronic state of a region of the surface of a zeolite. However, aU these techniques are destructive ones, and for that reason other methods such as isotopic-transient experiments or reflectance [16] and fluorescence [17] imaging can be used to estimate the effective membrane thickness. 

Veirs, D.K., Ager, J.W., Loucks, E.T. and Rosenblat, G.M. (1990) Mapping materials properties with Raman spectroscopy utilizing a 2-D detector. Appl. Opt., 29, 4969 1980. 

Table I, shows the spectrometers recently developed by the authors. All are based on the principle of multichannel spectroscopy utilizing image devices as sensors (1). In these spectrometers, a spectrum is scanned rapidly electronically, typically in 10 ms. Spectral data can be readily available ina digitized form, the sensitivity of these image devices is generally better than...

Each of the alkali metals has at least one NMR active nucleus (Table 10.1), although not all nuclei are of sufficient sensitivity to permit their routine use. For examples of NMR spectroscopy utilizing i -block metals, see Section 2.11 and worked example 18.1. 

Aim multipass cell for i.r. spectroscopy, utilizing two parallel concave mirrors, has allowed path lengths up to 150 m to be achieved. For a study of collision-induced simultaneous transitions in binary gas mixtures, a 2m sample cell has been constructed that allows pressure variation up to 1500 bar. A cell has been designed for pressures up to lOKbar and temperature variation over the range 10—300 A Pfund-type cell has been constructed for i.r. spectroscopy with... 

Fourier transform infrared (FTIR) spectroscopy has been used extensively in the past several years in the study of coal and its related products (1-13). The majority of this work has been done by transmission spectroscopy utilizing the KBr pellet technique. 

The absolute configuration of the phosphorus atom in optically active phospholene oxides was assigned by UV/CD spectroscopy utilizing theoretical calculations." ... 

Muller L (1979) Sensitivity enhanced detection of weak nuclei using heteronuclear multiple-quantum coherence. J Am Chem Soc 101 4481-4484 Mueller L, Schiksnis RA, Opella SJ (1986) Proton-detected natural-abundance N NMR spectroscopy utilizing constant-time multiple-quantum excitation. J Magn Reson 66 379-384... 

Effective Reaction Monitoring of Intermediates by ATR-IR Spectroscopy Utilizing Fibre Optic Probes... 

Light is electromagnetic radiation to which the retina of the eye is sensitive, but electromagnetic radiation also includes regions identified as infrared, ultraviolet, x-ray, gamma-ray, and radiofrequency radiation. Atomic spectroscopy utilizes primarily the ultraviolet and visible regions of the electromagnetic spectrum. It is important therefore to understand some of the basic characteristics and properties of such radiation. 

Since atomic absorption spectroscopy utilizes the ground state atom population for its measurements, it would appear that atomic absorption has a great advantage over flame emission in terms of detection limits and sensitivities of detection. An inspection of Appendix VIII, where detection limits are given for a number of elements for flame emission and atomic absorption, indicates this is not true. The reason for this apparent discrepancy lies in the relative stabilities of ground state and excited state atoms. An excited atom has a lifetime of the order of 10 -10 sec, and thus emits its energy very quickly after being excited. The usual flame emission source has an upward velocity of from 1 to 10 m/sec, so the excited atom will move only about 10 -10 m between the time of excitation and emission. 

Analogously to the LMR technique, Stark spectroscopy utilizes the Stark shift of molecular levels in electric fields to tune molecular absorption lines into resonance with lines of fixed-frequency lasers. A number of small molecules with permanent electric dipole moments and sufficiently large Stark shifts have been investigated, in particular, those molecules that have rotational spectra outside spectral regions accessible to conventional microwave spectroscopy [146]. 

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