Single channel spectrum

OPUS differentiates between the Raman spectrum and the single channel spectrum. The single channel spectrum of the Stokes and anti-Stokes Raman scattering for a sulphur sample is shown in Fig. 4.4. Note that the abscissa here is expressed in absolute wavenumbers. Therefore, the exciting laser line appears at vl = 9394 cm and the bands at wavenumbers lower and higher than 9394 cm arise from Stokes and anti-Stokes Raman scattering, respectively. On the other hand, a standard Raman spectrum comprises the spectral range from 0 to 3500 cm. Load the file RAMAN SULPHUR and find out the difference between these two types of spectra. 

Let us illustrate this conversion. The Raman spectrum of diamond shows a sharp band at 1331 cm. Assuming RLW = 9394 cm this band appears at 8063 cm in the single channel spectrum. As another example. Fig. 10.25 shows both types of spectra for ethanol on the left there is the Raman spectrum over the range from 100 to 3500 cm and on the right the single channel spectrum between 5894 and 9294 cm . Notice that the spike at 9394 cm is due to the laser line. 

Figure 10.25. The Raman spectrum and single channel spectrum of ethanol. 

The wavenumber region and data point spacing, as well as the units of the x-axes will be taken from a single channel spectrum that is entered in the black-... 

Mertz signed The modified Mertz function is used, if the single channel spectrum is expected to contain negative contributions. 

Keep in mind that the transformation interferogram to spectrum always results in a single channel spectrum. Therefore, a calculated spectrum must be converted in a respective way. 

Again, it is advised that, if the interferogram is perfectly symmetric or perfectly antisymmetric, you should select the symmetric transformation. Define the data range used for the transformation on the Frequency Range page and start the transformation. The result is a single channel spectrum. In the case of an antisymmetric transformation only the real part of the single channel spectrum will be saved. 

Note the total absorptions by water vapour bands in the single channel spectrum (left) and the discontinuity in the resulting absorption spectrum (right panel). See text and captions of Figures 6.1 and 6.2 for further details. 

Photomultipliers are used as detectors in the single-channel instruments. GaAs cathode tubes give a flat frequency response over the visible spectrum to 800 nm in the near IR. Contemporary Raman spectrometers use computers for instrument control, and data collection and storage, and permit versatile displays. 

Figure 1.33 The underlying principle of the Redfield technique. Complex Fourier transformation and single-channel detection gives spectrum (a), which contains both positive and negative frequencies. These are shown separately in (b), corresponding to the positive and negative single-quantum coherences. The overlap disappears when the receiver rotates at a frequency that corresponds to half the sweep width (SW) in the rotating frame, as shown in (c). After a real Fourier transformation (involving folding about n = 0), the spectrum (d) obtained contains only the positive frequencies.

Figure 3. Pulse height spectrum of gamma radiations. Window of single channel analyzer fixed to optimize intensity of 14.4-k,e,v, radiation...

Once we have the appropriate nuclide, we must separate the radiation of interest from all other radiation present. A typical gamma spectrum is shown in Figure 3 for cobalt-57 in palladium. The radiations which can be identified include the 6-k.e.v. x-ray, the 14-k.e.v. y-ray of interest, and a sum peak and palladium x-ray peak, both lying at about 21 k.e.v. If one now sets the single-channel analyzer window correctly, one observes essentially only the 14-k.e.v. peak, but all of this is not recoil-free radiation it includes other radiation which falls into the window from various gamma quantum de-excitation processes. 

Researchers have oscillated between emphasizing specificity of neurons ( labeled lines ) and responses to a spectrum of tastants by one cell. More recently, patterns of activation of a number of sensory cells are favored for coding specific taste sensations (Smith and Margolskee, 2001). Neural distinction of different tastes requires simultaneous activation of different cell types. The brain receives a single channel of information, simply bitter for a number of different compounds. 

The irregularity of the spectrum has consequences on the properties of the matrix elements of observables like the electric dipole moment and, thus, on the radiative transition probabilities. For radiative transitions, a single channel is open and the statistics of the intensities follow a Porter-Thomas or x2 distribution with parameter v = 1, as observed in NO2 [5, 6]. 

Smaller values of are obtained for interferometers operated in a double-beam mode, since the moveable mirror must be left stationary for a fraction of the cycle time to allow the detector to stabilize each time the beam is switched from the sample to the reference position. With an optical null grating spectrometer the chopper is used not only to modulate the beam but also to alternate the beam between sample and reference channels. Thus, it takes approximately the same time to measure a transmittance spectrum using a double beam optical null spectrometer as it takes to measure a single-beam spectrum with the same S/R. Hence, for this type of spectrometer may be assigned a value of 2. 

Intensity Coding/Coupling. The intensity coding/coupling tool combines channel pairs or multiple channels and transmits only a single channel plus directional information for parts of the spectrum. 

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