Continuous wave spectrum

Time The excitation lasts some ten or so microseconds and the return to equilibrium generally less than 10 seconds. A continuous wave spectrum lasts in the region of 4 to 5 minutes. 

The inherent low sensitivity of C NMR requires that the results of at least a few hundred, and normally several thousand, spectra be averaged in order to be able to detect the absorption peaks above the noise in a normal sample. Since a single continuous-wave spectrum takes between 100 and 500 seconds, simple signal averaging in order to obtain satisfactory signal-to-noise ratios is generally prohibitive. 

Line width from continuous-wave spectrum in the absorption mode. CF indicates that fitting of experimental spectra to a Lorentzian curve was performed. 

Line width from continuous-wave spectrum in the dispersion mode. 

In this approach one uses narrow-band continuous wave (cw) lasers for continuous spectroscopic detection of reactant and product species with high time and frequency resolution. Figure B2.5.11 shows an experimental scheme using detection lasers with a 1 MFIz bandwidth. Thus, one can measure the energy spectrum of reaction products with very high energy resolution. In practice, today one can achieve an uncertainty-limited resolution given by... 

In the continuous wave (CW) experimental setup a sample is constantly illuminated by a probe beam and the steady state change in the transmission is detected (see Fig. 7-1). An argon ion laser has been used to generate the pump beam and the probe beam was from an incandescent lamp (tungsten or others), producing a broad spectrum (0.5 to 5 pm) [6]. Both pump and probe beams are directed onto the sample film and the transmitted probe light is collected, filtered through a monochromator, and detected by a photodetector. Both the pump and the probe... 

C60 has been used to produce solvent-cast and LB films with interesting photoelec-trochemical behavior. A study of solvent-cast films of C60 on Pt rotating disc electrodes (RDEs) under various illumination conditions was reported [284]. Iodide was used as the solution-phase rednctant. The open-circuit potential shifted by 74 mV per decade of illumination intensity from a continuous wave (cw) argon-ion laser. The photocurrent versus power was measured at -0.26 V under chopped illumination (14-Hz frequency, vs. SCE) up to 30 mW cm and was close to linear. The photoexcitation spectrum (photocurrent versus wavelength) was measured at 0.02 V (vs. SCE) from 400 to 800 mn and found to be... 

Continuous wave A method of recording an NMR spectrum in which the field B] is applied continuously and either the magnitude of Bo or the radiofrequency is varied so that the nuclei are brought successively into resonance. 

Historically, this has been the most constrained parameter, particularly for confocal laser scanning microscopes that require spatially coherent sources and so have been typically limited to a few discrete excitation wavelengths, traditionally obtained from gas lasers. Convenient tunable continuous wave (c.w.) excitation for wide-held microscopy was widely available from filtered lamp sources but, for time domain FLIM, the only ultrafast light sources covering the visible spectrum were c.w. mode-locked dye lasers before the advent of ultrafast Ti Sapphire lasers. 

The typical way to open a billiard is to attach some reservoirs with continuous energy spectrum, for example, the leads or microwave waveguides, as shown in fig. 3 below. Full information about the scattering properties of the billiard is given by the scattering wave function which is a solution of the Schrodinger equation Hip = Exp with the total Hamiltonian... 

Fourier transform spectroscopy technology is widely used in infrared spectroscopy. A spectrum that formerly required 15 min to obtain on a continuous wave instrument can be obtained in a few seconds on an FT-IR. This greatly increases research and analytical productivity. In addition to increased productivity, the FT-IR instrument can use a concept called Fleggetts Advantage where the entire spectrum is determined in the same time it takes a continuous wave (CW) device to measure a small fraction of the spectrum. Therefore many spectra can be obtained in the same time as one CW spectrum. If these spectra are summed, the signal-to-noise ratio, S/N can be greatly increased. Finally, because of the inherent computer-based nature of the FT-IR system, databases of infrared spectra are easily searched for matching or similar compounds. 

It is observed that the infrared spectrum obtained with a continuous wave infrared spectrometer has increasing resolution as the scan speed is decreased. Explain this observation. 

Fig. 9. The continuous wave EPR spectrum of recombinant Rhodnius prolixus NPl-histamine at a microwave frequency of 9.338 GHz (trace 1) and field-sweep ESE spectra at 8.706 GHz (trace 2), 3.744 GHz (trace 3), 3.065 GHz (trace 4). Dashed arrows show the changes in magnetic fields corresponding to principalg -values at the different microwave frequencies. Inset trace 1, the primary ESE decay recorded at 8.706 GHz, Bo = 213 mT (the low-field turning point in the field-sweep ESE spectrum shown by trace 2 in the main panel). Inset trace 2, the primary ESE decay recorded at 3.065 GHz, Bo = 140.8 mT (the high-field turning point in the field-sweep ESE spectrum shown by trace 4 in the main panel). Reproduced with permission from Ref. (89).

The easiest way to reduce the amplitude of TOCSY cross peaks in the ROESY spectra is to record a spectrum with minimal spin-lock power [23]. The other possibility is to modulate the frequency of the spin-lock field [25]. However, the most convenient way is to apply a series of 180° pulses instead of a single continuous-wave pulse during the mixing time, as is done in the T-ROESY experiment. Figure 4(D) shows the T-ROESY spectrum of cyclo(Pro-Gly) recorded with = 300 ms. Although the... 

One of the main advantages of FT spectrometers is that, since the FID is in digital form, we can repeat the excitation/detection process a number of times and all the resulting scans can be added and the FT performed on the resultant FID. In this way, we can improve the signal-to-noise ratio and can detect nuclei which are not very abundant (e.g. C) or have low sensitivity to NMR (see Section 4.2). These nuclei could not have been detected on the older continuous wave instruments, as the spectrum was the result of a single scan, obtained as one of the frequency or magnetic held were varied while keeping the other constant. 

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