Repetitive scanning high resolution

High-resolution CP/MAS spectra of (natural abundance 0.37% and y( N) = —O.lOly( H)) can also be obtained from samples with natural abundance. In this case, the experimental parameter that shows a higher variation is the contact time that is generally set to 6 ms, the number of repetitions (scans) is usually greater than in the case of spectra, leading to longer experimental times. 

Scan speed Repetition rate, exactness, resolution Routine fast high resolution slow ... 

In this paper we report studies that are a continuation of our previously reported work (Chance et al., 1983) and all NMR spectra were obtained using tissue extracts prepared after rapidly freezing hearts perfused for different periods of time up to steady state isotopic equilibrium following replacement of normal substrates with labeled substrates. With this approach, a large number of scans can be accumulated (typically 2000 with a repetition time of 2 s) and high resolution of the line splittings due to spin coupling between adjacent... 

Fig. 1. High-resolution spectrum of ATP. (a) 1959 Single-scan, 24.3-MHz, 5-mm tube, continuous-wave operation of a Varian 4302 dual-purpose NMR spectrometer. [ATP] = 500 mM. (b) 1976 10 scans, 72.9 MHz, 20-mm tube, in the Fourier-transform mode of operation, 20-sec repetition rate, and proton decoupling on a Bruker WH 180 NMR spectrometer. [ATP] = 1 mM. From Cohn (1979).

The sample frequency of the ADC (analogue to digital converter) should be 8 times higher than the test frequency (centre frequency of the spectrum). In dependence of the application, different ADC- boards are used. A standard board (20520) provides 8 bit resolution and up to 100 Msamples/s in single shot mode. For manual tests, up to 400 Msamples/s can be reached in the repetition mode. For scanning systems with high frequencies boards up to 400 Msamples/s (single shot) are available. 

The femtosecond pump-probe absorption spectroscopy was used for the investigation of the SI-photoisomerization of cis-stilbene in compressed solvents [20]. The authors of the work [21] demonstrated a technique for femtosecond time-resolved optical pump-probe spectroscopy that allowed to scan over a nanosecond time delay at a kilohertz scan rate without mechanical delay line. Two mode-locked femtosecond lasers with 1 GHz repetition rate were linked at a fixed difference frequency of =11 kHz. One laser delivers the pump pulses, the other provides the probe pulses. The techniques enabled high-speed scanning over a 1-ns time delay with a time resolution of 230 fs. 

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