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Transient-response spectrometer

The low MW power levels conuuonly employed in TREPR spectroscopy do not require any precautions to avoid detector overload and, therefore, the fiill time development of the transient magnetization is obtained undiminished by any MW detection deadtime. (3) Standard CW EPR equipment can be used for TREPR requiring only moderate efforts to adapt the MW detection part of the spectrometer for the observation of the transient response to a pulsed light excitation with high time resolution. (4) TREPR spectroscopy proved to be a suitable teclmique for observing a variety of spin coherence phenomena, such as transient nutations [16], quantum beats [17] and nuclear modulations [18], that have been usefi.il to interpret EPR data on light-mduced spm-correlated radical pairs. [Pg.1566]

The TAP-2 reactor system [4] was used to perform transient response experiments under vacuum and at temperatures ranging from 300 to 400°C. A carbon loading of 100 mg was placed between two layers of quartz particles (0.2-0.3 mm particle size). Neon was used as an internal standard for calibration and as a reference for diffusion. Nitric oxide and neon were introduced by pulses in the microreactor (25.4 mm in length and 4 mm in diameter) in a volume ratio of 1 1. The reactor was continuously evacuated and the response of the pulses as a function of time was analysed on -line by a quadrupole mass spectrometer. [Pg.256]

Figure 2. Electrical schematic for the transient response dielectric spectrometer. Figure 2. Electrical schematic for the transient response dielectric spectrometer.
Nuclear spins with different electronic environments may be brought into resonance by either one of two techniques. In the frequency-sweep method, the spectrum is recorded by sweeping the applied radiation frequency. In the transient-response method, the transient signal for its component frequencies is sorted/transformed after an induction (by pulse(s) of an applied field in terms of angles, e.g. 90° or 180°) of transient response in the system. The transient signal is changed into a normal spectrum by Fourier transformation in the transient-response method, which is used by most modem NMR spectrometers. There are four parameters that define the NMR spectrum ... [Pg.199]

FIGURE 51.2 Normalized Ar transient response detected by mass spectrometer following He-He/Ar step change. Curves A and C are obtained without proper adjustment of the pressure drop in the feed lines. Curve B corresponds to equal values of pressure drop in the feed Unes. [Pg.1230]

FUV transient absorption spectrometer based on TRATR has also recently been developed and tested for aqueous solutions of phenol and tryptophan in the region of 170-185 nm [61]. In this region, a stable tunable laser was not available, and thus, white light from a laser-driven Xe lamp source was employed. The time resolution, which was determined by the time response of a continuous light detector, was 40 ns. [Pg.6]

The Imass Dynastat (283) is a mechanical spectrometer noted for its rapid response, stable electronics, and exact control over long periods of time. It is capable of making both transient experiments (creep and stress relaxation) and dynamic frequency sweeps with specimen geometries that include tension-compression, three-point flexure, and sandwich shear. The frequency range is 0.01—100 H2 (0.1—200 H2 optional), the temperature range is —150 to 250°C (extendable to 380°C), and the modulus range is 10" —10 Pa. [Pg.199]

A spectrometer with rapid response electronics should be used for electrothermal atomization, as it must follow the transient absorption event in the tube. Automatic simultaneous background correction (see Section 2.2.5.2) is virtually essential, as non-specific absorption problems are very severe. It is important that the continuum light follows exactly the same path through the furnace as the radiation from the line source (assuming a deuterium lamp is being used rather than Smith-Hieftje or Zeeman effect). The time interval between the two source pulses should be as short as possible (a chopping frequency of at least 50 Hz) because of the transient nature of the signal. [Pg.58]

An important test of a transient spectrometer s accuracy, stability, and noise level is provided by a baseline spectrum. This is an averaged spectrum obtained in exactly the same way as actual data, except that the ultraviolet excitation beam is kept blocked when it would otherwise be open. The lowest trace shown in Figure 2 is a typical 5-cycle baseline spectrum for our system. Systematic deviation from zero is less than 0. 01 absorbance units throughout, and the r. m. s. noise level varies from 0. 03 near the edges to 0. 007 near the center of the spectrum. These noise variations are inversely related to the detected single beam intensity spectrum, which drops on the blue side because of the continuum distribution and the transmissive properties of our beam combiner, and on the red side because of the photocathode response of the SIT detector head. A high degree of intensity linearity in the OMA is necessary for our... [Pg.231]

In addition to the normal requirements of a good atomic absorption spectrometer two parameters are of paramount importance when employing a furnace as the atomising source. These> are (a) the response time of the signal handling circuitry must be sufficiently rapid to capture the transient absorption signals which are characteristic of furnace atomisers, and (b) the... [Pg.55]

Mass spectra of short-lived, unstable episelenides were obtained by taking advantage of a mass spectrometric technique developed for the time-resolved detection of transient intermediates in flash-photolyzed systems <66JA4277>. Detection does not depend on the electronic absorption characteristics of the transient, and, in combination with kinetic absorption spectroscopy, the technique assumes great flexibility. The apparatus consists, essentially, of a photolysis cell attached to a small leak into the ion source of an Atlas CH4 mass spectrometer. Selected mass peaks can be studied with a response time of a few milliseconds, and thereafter at times limited by bleeding of the photolyzed mixture into the ion chamber. Typical photolytic flash energies were 480 calories, passed into a reaction volume of 5 ml. [Pg.263]


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See also in sourсe #XX -- [ Pg.290 , Pg.291 ]




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