Frequency center

Microwave frequency Center field Modulation frequency Modulation phase... 

In Chapter 2, ENDOR (electron-nuclear double resonance) was briefly described. To perform an ENDOR experiment it is necessary to apply both a radiofrequency and a microwave frequency, effectively performing simultaneous NMR and ESR, respectively, on the sample. The experiment is performed at a fixed magnetic field, with the ESR saturating frequency centered on a... 

A graph of the resonant frequencies over a very narrow range of frequencies centered on the fundamental resonant frequency of the nucleus of interest (e.g., 13C at 50.000 MHz) is called a spectrum, and each peak in the spectrum represents a unique chemical environment within the molecule being studied. For example, cycloheptanone has four peaks due to the four unique carbon positions in the molecule (Fig. 1.3). Note that symmetry in a molecule can make the number of unique positions less than the total number of carbons. 

FIGURE 6.9 (a) Schematic representation of an AMX spectrum, showing the spin states associated with each spectral line. The situation depicted is that for all three fs positive. The signs of m are indicated. (b) Spectrum of 2,3-dichloropyridine at 60 MHz, an example of an AMX spin system. (c-e) Results of selective decoupling in 2,3-dichloropyridine, with decoupling frequencies centered between the following lines (c) Mi and M2, (d) M3 and M4, (e) and A2. 

The quantity e qQlh, termed the quadrupolar coupling constant, is a function of the chemical environment of the deuteron. For example, in hexane e qQlh = 168 kHz (Burnett and Muller, 1971). Note that this quantity is independent of the magnetic field strength. NMR doublets are centered about the Larmor frequency, but in practice this frequency is subtracted away, so spectra are generally shown plotted as a function of frequency, centered on zero. The minimum observed frequency is v jn = -3l4 e qQ/h), and the maximum is = 3l4(e qQlh). (A very readable quantitative introduction to NMR studies of nuclei having quadrupole moments is given by Cohen and Reif, 1957). 

Drive harmonics are a function of the drive switching frequency and pattern, and will differ between suppliers. The TMEIC P30 source converter is a medium voltage, IGBT, PWM regenerative source converter using a 1,536-Hz modulation frequency that is asynchronous to the utihty frequency. Harmonics created by the source converter are sideband frequencies centered around integer multiples of this carrier frequency (i.e., when applied on a 60 Hz utihty, the sidebands with series that will be) ... 

Both aromatic and aliphatic sulfonyl halides react with the iridium(I) complex (XI) to form octahedral S-bonded sulfinate derivatives such as (XLIX) 3S), These are characterized by intense infrared stretching frequencies centered near 1235 and 1065 cm , reminiscent of sulfones. The low frequencies of these absorptions suggest that the S-bonded sulfinate group is a strong ar-acid. Certain of the aromatic sulfinates eliminate SO2 upon heating, yielding iridium(III) aryls such as (L) 38). The scope of this gas-forming elimination reaction is uncertain. 

The frequency components involved in the real-time spectra were extracted by a Fourier analysis of the normalized pump probe data (see Fig. 3.22a for excitation with A = 620 nm, and Fig. 3.22b for 642 nm). Both Fourier spectra are dominated by a band of frequencies centered around 107.8 cm" and 111.3 cm" for the respective wavelengths. This main frequency band contains the frequencies of the energy spacings of neighboring vibronic levels (i.e. Av — 1), simultaneously excited by the spectrally broad femtosecond laser pulse. An additional frequency group with lower amplitude appears for both experiments, around 214 cm" in Fig. 3.22 a and around 222 cm" in Fig. 3.22b. This contribution appears to be due to the fact that... 

If the absorbed infrared radiation excites both vibrational and rotational changes in the molecule, instead of a single frequency of infrared radiation v, a band of frequencies centered about Vi will be observed for the fundamental band. For example, the fundamental absorption band of HCl is shown in Figure 4-1. The band center is at 2886 cm and the band envelope has a width of about 150 cm L If the band is examined at low gas pressures and under high resolution, a series of maxima are seen, as shown in Figure 4-IB (located... 

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