Spectral dispersion

In Problem 50 we start by showing you how the proton spectrum varies depending on the spectrometer s magnetic field. The increased spectral dispersion at 600 MHz makes quite a difference The multiplets look completely different, as you can see better in the expansions. Even at 600 MHz spectrum simulation will be required for a complete determination of the coupling constants, but we can simplify the multiplets quite a bit using NOESY and TOCSY. 

Note that the increased spectral dispersion at 600 MHz leads to less complicated multiplets and also in one case to the separation of signals which overlap at 200 MHz. 

The commercially available laser source is a mode-locked argon-ion laser synchronously pumping a cavity-dumped dye laser. This laser system produces tunable light pulses, each pulse with a time duration of about 10 picoseconds, and with pulse repetition rates up to 80 million laser pulses/second. The laser pulses are used to excite the sample under study and the resulting sample fluorescence is spectrally dispersed through a monochromator and detected by a fast photomultiplier tube (or in some cases a streak camera (h.)) ... 

The sensitivity on the other hand is dictated by the spin density and the polarization (the relative population of a- and y3-states). The latter in turn depends on the energy separation of a- and y3-states, which increases concomitantly with field strength. Changing to a higher field will therefore not only increase spectral dispersion but also increase sensitivity because the polarization increases. The remarkable increase in resolution that is gained by going from 600 to 800 MHz is shown in Fig. 3.1. 

We performed femtosecond infrared pump-probe experiments, using pulses with a bandwidth of 200 cm"1 (FWHM). A small fraction of the infrared pulses was split off to obtain a broadband probe pulse, which was spectrally dispersed after interaction with the... 

Peng Y. and Lohmann U. (2003). Sensitivity study of the spectral dispersion of the cloud droplet size distribution on the indirect aerosol effect. Geophys. Res. Lett., 30(10), 14/1-14/4. 

FIGURE 2.1 51V NMR spectrum showing aqueous vanadate in the presence of A/fV-dimeth-ylhydroxylamine and dithiothreitol. The wide spectral dispersion of the signals is characteristic of vanadium NMR spectra. 

When the image of elongated excitation sources, e.g., arcs, flames, plasmas, etc., is focused along the slit height of a polychromator, the spatial intensity information (vertical axis) is accurately relayed to the exit focal plane, concurrently with the horizontal spectral dispersion. Thus, by (electronically) dividing the target into a few tens of tracks, the entire spectral profile of these sources can be simultaneously observed and quantitatively studied. 

Required lenses. The field lens (fl = 95 mm), Fig. 1C and D, k, see Section II, b. 2., collecting all the light from the objective produces an image of the objective pupil near the reflection grating used for spectral dispersion or the mirror substituted for topographic operation. This ensures that all the available photons reach the effective area of the grating or mirror. 

Despite the general improvement in spectral dispersion observed at high field-strengths, some examples of monosaccharide derivatives have been reported86-88 for which 220-MHz spectra failed to give more readily interpretable results, or more information, than had been obtained at 100 MHz. 

The general construction of an atomic absorption spectrometer, which need not be at all complicated, is shown schematically in Fig. 1. The most important components are the light source (A), which emits the characteristic narrow-line spectrum of the element of interest an absorption cell or atom reservoir in which the atoms of the sample to be analysed are formed by thermal molecular dissociation, most commonly by a flame (B) a monochromator (C) for the spectral dispersion of the light into its component wavelengths with an exit slit of variable width to permit selection and isolation of the analytical wavelength a photomultiplier detector (D) whose function it is to convert photons of light into an electrical signal which may be amplified (E) and eventually displayed to the operator on the instruments readout, (F). 

Infrared and Raman spectrometers usually combine a radiation source, a sample arrangement, a device for spectral dispersion or selection of radiation, and a radiation detector, connected to appropriate recording and evaluation facilities. An ideal spectrometer records completely resolved spectra with a maximum signal-to-noise ratio. It requires a minimum amount of sample which is measured nondestructively in a minimum time, and it provides facilities for storing and evaluating the spectra. It also supplies information concerning composition, constitution, and other physical properties. In practice, spectrometers do not entirely meet all of these conditions. Depending on the application, a compromise has to be found. 

In the NIR, and, more rarely, in the MIR, interference filters are sometimes employed for spectral dispersion. Sets of individual filters and variable circular filters are used especially in simple spectrometers for production control and environmental monitoring. 

The spectral dispersion for organosilicones may be considerable for certain families of compounds. This is reflected in the Si chemical shifts of siloxanes, -(SiRR 0) -, an important class of compounds which includes resins, fluids, room-temperature vulcanized and heat-cured rubber consumer products. The first, Si NMR results (5,78) reported on polydimethylsiloxanes showed that individual resonance... 

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