Dark spectrum

The CIDNP spectrum is shown in figure B 1.16.1 from the introduction, top trace, while a dark spectrum is shown for comparison in figure B 1.16.1 bottom trace. Because the sign and magnitude of the hyperfine coupling constant can be a measure of the spin density on a carbon, Roth et aJ [10] were able to use the... 

Fig. 31. H CIDNP spectra (90 MHz) observed during the photoreaction of chloranil with the 6-methoxy-5-methylene-l, 2,3,4,6-pentamethyl-bicyclo[2.2.0]hex-2-ene (94) (0.02 M each in acetone-d6). The bottom trace is a dark spectrum...

FIGURE 11. H NMR spectra of the reaction mixture of Et3SnCH2CH=CH2 with CCRBr in C-C6D12 under a sequential saturation (apphcation of an RF field) to the proton groups (a) initial spectmm (h) under irradiation with saturation of the protons of the precursor at position 3, (c) dark spectrum with saturation of the protons of the precursor at position 3, (d) the resulting... 

FIGURE 13. H CIDNP effects in the photolysis of Et3GeCH2CH=CH2 (13) in the presence of CCFBr in c-C Da (a) initial spectrum, (b) under UV irradiation, (c) dark spectrum, (d) after the photolysis. The part of the spectram associated with the ethyl groups is omitted... 

A very strong Si - H band was observed by Peter et al. [11] during photocorrosion measurements of Si in NH4F. The band at 2100 cm appeared during illumination and persisted over several minutes in the dark spectrum. It was thus concluded that the band is not related to intermediates of the photocurrent but to relatively stable, long-lived species. 

Fig. 4.3. (D and E) Primary electron acceptor (A 12) electron acceptor X. (D) Light>dark spectrum of the electron acceptor X in PSI-RC, recorded at 5°C and —0.62 V — the broad band at 450-550 nm is attributed to an FeS center and the other changes to electrochromic effects (from Ref. 57). (E) ESR spectrum of X in PSI-RC, measured at 10 K (from Ref. 290).

The statement that the dark noise equals is simple enough, but it does have some practical consequences. When the dark spectrum is subtracted from the Raman spectrum obtained with the same integration time, the noise on the spectrum will increase according to ... 

Figure 8.32. Temperature dependence of dark spectrum for an EEV 15-11 deep depletion CCD. Integration time was 60 sec in all cases. Positive spikes are due to cosmics negative spike at 1450 cm is due to a column in this CCD with weak response.

The nuances of bias, dark signal, and binning can be complex at times, and detailed discussions are available (21, 26-29). A simple procedure that avoids most pitfalls is subtraction of a blank from the observed Raman spectrum obtained under the same conditions of binning, temperature, and total integration time. The blank includes the dark spectrum and bias, as well as scattering from solvent, cell, optics, and the like. 

For CL spectra we found it critical to obtain a "dark" spectrum immediately before automated initiation of the reaction by injection of the final reagent and acquisition of the CL spectrum. Subtraction of the dark spectrum from the CL spectrum compensates for dark signal drift. Also, signal averaging of many spectra (one from each reaction run) is often essential to achieve a reasonable S/N. 

Fig. 12. S[ multiline signal. In (a) the spectrum (parallel polarization EPR) labeled Dark represents a dark-adapted PS II sample thus, it is in the S, state. The second trace represents the sample following illumination with light to generate S2. The top, Dark, spectrum minus the middle, Illuminated, spectrum yields the third spectrum in (a). This represents a well-resolved multiline signal arising from a multinuclear exchange coupled paramagnetic Mn cluster (174) in the S, state of the OEC. If the subtraction is reversed and the spectra are recorded using perpendicular polarization, then when the Dark spectrum is subtracted from the Illuminated spectrum, an S2 multiline signal is readily observed (b). [Reproduced with permission from (174). Copyright 1998 the American Chemical Society.]...

Compare this value with those we obtained from the dark spectrum of CPI,we found the conformation largely changed, helix released, -pleated sheet increased, the decreasing of helix may be important in chemical reaction and energy transfer. 

Fig. 4. ESR spectra of Fx in the Photosystem I core protein after illumination during freezing. (A) Light-minus-dark spectrum of native-Fx (B) Light-minus-dark spectrum of apo-Fx (C) Light-minus-dark spectrum of reconstituted-Fx. The samples were suspended in 50 mM Tiis, pH 8.3 containing 1 mM ascorbate and 0.3 mM DCPIP at 500 ig Chl/ml. The spectra were resolved by subtracting the light-off from the light-on spectrum and amplifying 3.5-fold in software. Spectrometer conditions temperature, 6 K microwave power, 40 mW microwave frequency, 9.101 GHz receiver gain, 5 x 10 modulation amplitude, 40 G at 100 kHz.

N-acetyl tyrosine and 2 x 10 M flavin I taken with the pulse sequence of Figure 1, (a) light sjoectrum (0.4 sec laser irradiation, 5 W, (b) dark spectrum, (c) difference a-b. 

Figure 8. 360 MHz nmr spectra of 2 x 10 M HEW lysozyme and 4 X 10 M flavin I in D2O (pH = 5.4, temp. 55°C) taken with the pulse sequence of Figure 1 (a) light spectrum, (b) dark spectrum, (c) difference a-b. Polarized flavin lines are indicated by F6, F8 and FlO. Trp I and Trp II denote lines belonging to two tsryptophan residues (see text) ...

A) the light spectrum (B) the dark spectrum (C.) photo CIDNP difference spectrum i.e. spectrum A minus spectrum B (D) photo CIDNP difference spectrum of gene-5 protein dissolved in 5.6 M guanidine HCl. 

Figure 6. Effect of the binding of the tetranucleo-tlde d(pC-K3-C-G) to gene-5 protein. Aromatic part of the 360 MHz spectrum of gene-5 protein (A) dark spectrum (B) photo-CIDNP difference spectrum (C)...

Fig. 17 H-NMR spectral changes observed during the reaction of intermediate C with protons giving compound D in the dark (spectrum a) after 0.5 min photolysis (spectrum b) and after 2 min photolysis (spectrum C).

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