Spectral detectivity

Chemical Gas Detection. Spectral identification of gases in industrial processing and atmospheric contamination is becoming an important tool for process control and monitoring of air quaUty. The present optical method uses the ftir (Fourier transform infrared) interference spectrometer having high resolution (<1 cm ) capabiUty and excellent sensitivity (few ppb) with the use of cooled MCT (mercury—cadmium—teUuride) (2) detectors. 

Equation (3-178) suggests that a plot of A obs/[ROH] vs. [N] will be linear. Because the conversion to the intermediate is quantitative, [N] = [N]o — [AXJq. Plots according to Eq. (3-178) were linear, permitting ky and A in to be estimated. Turning to the acetic anhydride—alcohol system, it is inferred that (in the absence of water) itj/lLi is close to zero (Scheme XXIV). Although the intermediate could not be detected spectrally, its possible presence is admitted in the rate equation for the loss of anhydride ... 

In some cases, tetrahedral intermediates have been isolated or detected spectrally. ... 

Evidence for molecular chlorine or bromine as the attacking species in these cases is that acids, bases, and other ions, especially chloride ion, accelerate the rate about equally, though if chlorine dissociated into Cl" and Cl , the addition of chloride should decrease the rate and the addition of acids should increase it. Compound 27 has been detected spectrally in the aqueous bromination of phenol. ... 

The retinal Schiff base chromophore is embedded in rhodopsin with its transition dipole moment parallel to the plane of the discs, i.e., perpendicular to the direction of travel of the incoming photons. Absorption of a photon leads to a sequence of readily detectable spectral changes.37,46113,499,500 The relaxation times indicated in Eq. 23-37 are for 20°C. 

Development of laser-based explosive detection methods employing vibrational spectroscopy begins with characterization of the spectral signature of the explosive to be detected. Spectral signatures of interest are usually those of the neat condensed-phase... 

Yellow solid changing (r.t.) to brown (with DO detectable spectral changes, 123) or green/black lV(CO>4dppe] (125) solutions Uteri orate raiadly. 

The reaction with dimcthylsulfonium methylide probably proceeds through the intermediates (a) and (b). Intermediates of type (b) have been detected spectrally. 

Keywords, microwave spectroscopy chemical warfare agent detection spectral sensing molecular fingerprint. 

Cowley has done much to dissipate the belief that the Sr, Cr, Eu stars constitute a fairly homogeneous class (with the exception of the three maverick stars discussed above). The number of detectable spectral lines, and their intensities, of yttrium, barium and lanthanides [40] in 29 Ap and A , stars were carefully compared. In most of these stars, yttrium and lanthanum are unexpectedly scarce. The relative solar abundances of 12 lanthanides (altogether... 

Given sensor spectral sensitivity, to estimate sensor resolution of a measiuand one can use expression (7). Thus, assuming that the minimal detectable spectral shift in the peak position is (A/lp). (which is typically on the order of 0.1 nm in the visible spectral range if no advanced optical detection is used), then the minimum value of a measurand that can be detected by such a sensor is ... 

In a similar fashion, spectral sensitivity can be defined using (7) by detecting spectral shift in the bandgap center (wavelength of the fiber lowest loss) resulting in a spectral sensitivity Sx 5,300 nm/RIU. Assuming that 0.1 nm spectral shift in the position of a bandgap center can be detected reliably, this results in the sensor resolution of Re(A a)miji 2 x 10 RIU, which is comparable to the resolution achieved by the amplitude method. 

Because transition states may have lifetimes of only several nanoseconds, in most cases, it is impossible to observe them directly. However, there are numerous lines of evidence for the existence of a tetrahedral-like transition state for non-enzymatic ester hydrolysis a) substitution at a carbonyl group (as is the case of the hydrolysis of esters) most often proceeds by a tetrahedral mechanism, a second-order addition-elimination (for a review of this mechanism, see (23)) b) the kinetics are pseudo-first order either in the substrate or in the nucleophile, as predicted by the mechanism c) for the 180 labeled esters, the 180 isotope is detectable in both products (in a "normal" Sjj2 reaction all the 180 isotopes should remain in the acid functionality)(24) d) in a few cases tetrahedral intermediates have been isolated or detected spectrally (25). 

Figure 43. Measured fluorescence decays for detection of the 1750 cm"1 band in the E>ib = 1420 cm-1 spectrum of anthracene for no carrier gas (top) and for 30 psig neon (bottom), all other conditions being the same (BW a 3 cm-1, R = 8.0 A, x = 3 mm). The relative lack of modulation in the neon decay compared to the decay of Fig. 41 top is primarily due to the poorer detection spectral resolution used in obtaining the former decay.

A method for overcoming this distortion by mechanically tuning the mirror spacing in synchronism with the tracked MMW source was described in a patent by Leskovar et al and has been developed by us as an analytical technique. The same source FM that is used to detect spectral profiles generates a frmdamental frequency component when swept over the cavity profile (Figure 2.11a). 

Fluorescence spectra were recorded at 77 K at different moments of the same treatment of the leaves in order to detect spectral changes which might be associated with the development of Fy. Fig. 3 shows the fluorescence spectra of 6-day-old leaves at time 20 and 90 min after the initial flash, thus before and after the development of Fy. The increase of the 657 nm band was due to the regeneration of the active protochlorophyll ide. At the same time, a slight but reproducible shift of the chlorophyll(ide) band towards longer wavelengths was observed. 

In the earlier decades of microwave spectroscopy, and in all commercial spectrometers on the market at that time, the method of choice was that of Stark modulation. A uniform electric field was applied to the entire sample and switched off and on, typically at a 33 kHz rate. The resulting phase coherently detected spectral frequency scan (Figure 1) shows a spectral line in phase with the switching voltage and a number of electric-field shifted (Stark) components in antiphase with it. 

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