Resolution of the spectrometer

Each vibrational peak within an electronic transition can also display rotational structure (depending on the spacing of the rotational lines, the resolution of the spectrometer, and the presence or absence of substantial line broadening effects such as... 

The hnearity between M and makes the concept of absorbance so usehil that measurements made by sampling methods other than transmission are usually converted to a scale proportional to absorbance. The linearity between M and i is maintained only if the resolution of the spectrometer is adequate to eliminate contributions from wavelengths not absorbed by the species being measured. In addition, the apparent value of a is very dependent on resolution because a is 2l strong function of wavelength (30,31). 

The widespread occurrence of long-range couplings in both furanose and pyranose derivatives explains why so many of the P.M.R. spectra of carbohydrate derivatives are apparently poorly resolved, even when the resolution of the spectrometer is above reproach. For example, the Hi resonance of the 1,6-anhydro-D-glucose derivative (12) is coupled to all of the other six ring protons. A further example of the line-broadening effect follows a consideration of the spectrum of 5,6-dideoxy-5,6-epithio-l,2-0-isopropylidene-/ -L-idofuranose for which the half-height... 

HREELS experiments [66] were performed in a UHV chamber. The chamber was pre-evacuated by polyphenylether-oil diffusion pump the base pressure reached 2 x 10 Torr. The HREELS spectrometer consisted of a double-pass electrostatic cylindrical-deflector-type monochromator and the same type of analyzer. The energy resolution of the spectrometer is 4-6 meV (32-48 cm ). A sample was transferred from the ICP growth chamber to the HREELS chamber in the atmosphere. It was clipped by a small tantalum plate, which was suspended by tantalum wires. The sample was radia-tively heated in vacuum by a tungsten filament placed at the rear. The sample temperature was measured by an infrared (A = 2.0 yum) optical pyrometer. All HREELS measurements were taken at room temperature. The electron incident and detection angles were each 72° to the surface normal. The primary electron energy was 15 eV. 

For the ascending limb moving towards the Earth the wavelength is blue-shifted to 656.273 nm and for the descending limb moving away from the Earth the red shift is 656.326 nm. These Doppler shifts place some demands on the resolution of the spectrometer but, as can be seen from Figure 3.2, this is possible for modern telescopes. 

The appearance of only one XPS peak for a mixed valence compound is consistent with a delocalized ground state (and excited state). Bifeirocenylene (II, III) picrate, whose structure is shown in Fig. 8, probably fits in this category. The Mossbauer spectrum of the complex indicates only one kind of iron atom, and the Fe 2p3,2 spectrum consists of only one peak with a weak shoulder at higher binding energy 29). It should be recognized, however, that even in the case of a localized system in which two XPS peaks are expected, if the chemical shift between the two peaks is less than the resolution of the spectrometer, only one peak will be observed. 

With this spectrometer, a difference mid-IR spectrum at a selected time after sample excitation is recorded by sweeping from 1640 to 940 cm in steps that may be as short as approximately equal to the spectral resolution of the spectrometer—in this case, 8 cm. The sample solution is pumped through a flow cell that has IR-transmitting Cap2 windows set with a 0.1-mm optical pathlength. The Bap2 windows have also been used for the sample cell. ... 

The decay of PN in pentane was monitored at 350 nm over a temperature range of 150-270 K, which allows direct measurement of kisc and accurate barriers to cyclization. The disappearance of singlet phenyinitrene at 298 K was faster than the time resolution of the spectrometer and the lifetime (r) of PN was estimated to be 1 ns under these conditions (vide infra). The lifetime of PN was measured in CH2CI2 at ambient temperature to be about 0.6 ns. " ... 

PAD (perturbed angular distribution) is a variation of PAC with nuclear excitation by a particle beam from an accelerator. QMS is quasielastic MdBbauer-spectroscopy, QNS is quasielastic neutron spectroscopy. For MOBbauer spectroscopy (MS), perturbed angular correlation (PAC), and /J-nuclear magnetic resonance (/3-NMR), the accessible SE jump frequencies are determined by the life time (rN) of the nuclear states involved in the spectroscopic process. Since NMR is a resonance method, the resonance frequency of the experiment sets the time window. With neutron scattering, the time window is determined by the possible energy resolution of the spectrometer as explained later. 

As in QMS, the degree of coherence is changed if the scattering atom itself jumps (with a frequency 1/r which is on the order of i/t , where t is determined by the time resolution of the spectrometer). The jumping atom transfers energy either to or from the scattered neutrons. As mentioned before, the result is a broadening (8v) of the elastic line. We expect Sv to vary exponentially with temperature. 

For the TOF SIMS analysis, only slides treated with a natural pH HAPS solution were used. These were subsequently extracted with warm and hot water. They were mounted into a grid sample holder for transportation into a VG IX23S time-of-flight (TOF) SIMS instrument operating at a vacuum of < 10 Torr with a microfocused liquid Ga metal ion primary beam source (30 keVx 1.0 nA). For charge compensation, an electron flood gun was used. The working resolution of the spectrometer was determined from a lead phthalocyanine spectrum for Pb+ at mlz = 208 and the molecular ion at mlz = 720, it was 500 and 1000, respectively. 

In the case of ET AAS, it is the far superior simultaneous BC and the visibility of the spectral environment (refer to Section 4.3.3) that dramatically contributes to an overall simplification of the procedure and to an increase in accuracy of the analysis. All things that are visible are much easier to understand and control than things that remain in the dark, as is the case with LS AAS. This is particularly true for all kinds of spectral events that might result in interference, although this risk is significantly reduced in HR-CS AAS thanks to the high resolution of the spectrometer. 

The spectrometer was a Physical Electronics Model 548 modified for emplacement in a glovebox so that actinide samples could be examined. Spectra were taken using AIK radiation (1486.6 eV). The overall energy resolution of the spectrometer was 1.2 eV using an analyzer pass energy of 25 eV. The spectrometer control was interfaced to a Nicolet 1180 minicomputer providing automatic data acquisition and analysis capability. 

Close A and slowly open the valve on the HCI cylinder. Fill the system to a pressure recommended by the instrnctor (50 to 500 Torr, depending upon the resolution of the spectrometer). Close the valve on the HCI cylinder and then close B and C. Remove the cell and take a spectrum at the highest available resolution. 

Sutherland predicted an observable (140 kHz) tunneling inversion in the ground vibrational state of PH3, on the basis of their calculated inversion barrier of 6000 cm . However, subsequent quantum chemical calculations have predicted [see a much higher barrier (between 10 000 and 14 000 cm ). A molecular-beam electric resonance spectrometer has been used to measure the ground state inversion splitting in PH3. It was found that the inversion splitting must be lower than the resolution of the spectrometer (1 kHz). Similarly, in a hi -resolution infrared study of the 41 2 band of PH3, Maki et aL found that the splitting of this level must be less than 0.02 cm". ... 

Comparison with Theoretical Calculations. It appears that the polymer valence bands are (very) difficult to interpret without the aid of a theoretical basis, or a model, or of the use of a reference spectrum obtained from a model compound. Indeed, Quantum Chemical theory is nowadays able to calculate band structure and density of states for polymers, to simulate the limited resolution of the spectrometer, and to modulate these theoretical density of states to account for the photoionization cross sections that vary considerably for valence bands of polymers containing different types of atoms, and electrons with various symmetries. Consequently, one is able now to predict theoretically the energies of the various molecular orbitals, but also... 

Figure 3.3-17 Relation between the optimal spectral band width Ai>o = t /Rp and the line width AC i/2, Rq is the resolving power of the spectrometer. For a the sensitivity is low since the spectral band width is larger than the line width, also the background contributes to the noise, for b the resolution of the spectrometer is sufficient to yield a high sensitivity, c Relation between bandwidth and resolving power.

The geometry of the experiment is shown in fig. 11.14. The axis of quantisation z is the direction of the light beam. The atomic sodium beam is incident in the x direction and the electron beam in the y direction. The schematic diagram also shows the 3px and 3py lobes of the target charge cloud for the 3pi substate. The scattering plane is the zy plane so that the component px of the recoil momentum p is observed in noncoplanar-symmetric kinematics. Because of the finite angular resolution of the spectrometer the components py and pz are of the order of 0.06 a.u. rather than zero. 

Interferences for AES can be classified into two main categories, spectral and matrix interferences. Spectral interference can occur as a result of an interfering emission line from either another element or the argon source gas, impurities within or entrained into the source, e.g. molecular species such as N2. Such interferences can be eliminated or reduced either by increasing the resolution of the spectrometer or by selecting an alternative spectral emission line. 

The function of the spectrometer is to accept as much light from the source as possible and to isolate the required spectral lines. This may be impossible where there is a continuous spectrum in the same region as the analytical line for example, the magnesium line of 286.2 nm coincides with a hydroxyl band. In direct reading instruments, electronic devices may be used to supplement the resolution of the spectrometer by modulating the intensity of the analytical signal. In absorption and fluorescence the light source is modulated in emission the spectral line is scanned (816) or the sample flow modulated (M23). 

Enantiotopic nuclei or groups are capable of fulfilling all or, at least, most of the foregoing symmetry-related expectations. Their chemical shifts depend, in addition, on both the medium in which the NMR experiment is conducted and the spectral resolution of the spectrometer. The latter is influenced by, for example, the magnetic-field strength. Enantiotopic groups are isochronous in achiral or racemic media and constitute A2,X2, etc., systems. Moreover, they are potentially anisochronous in chiral media. 

An example of a blank interference is the effect of Na emission at 285.28 nm on the determination of Mg at 285.21 nm. With a moderate-resolution spectrometer, any sodium in the sample will cause high readings for magnesium unless a blank with the correct amount of sodium is subtracted. Such line interferences can, in principle, be reduced by improving the resolution of the spectrometer. The user rarely has the opportunity to change the spectrometer resolution, however. In multielement spectrometers, measurements at multiple wavelengths can be used at... 

Molecular band emission can also cause a blank interference. This is particularly troublesome in flame spectrometry, where the lower temperature and reactive atmosphere are more likely to produce molecular species. As an example, a high concentration of Ca in a sample can produce band emission from CaOH, which can cause a blank interference if it occurs at the analyte wavelength. Usually, improving the resolution of the spectrometer will not reduce band emission, since tbe narrow analyte lines are superimposed on a broad molecular emission band. Flame or plasma background radiation is generally well compensated by measurements on a blank solution. 

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