Spectroscopy radiofrequency

Mismatch-optimized IS transfer Nuclear Overhauser enhancement Nuclear Overhauser effect spectroscopy Numerically optimized isotropic-mbdng sequence Preservation of equivalent pathways Pure in-phase correlation spectroscopy Planar doubly selective homonuclear TACSY Relayed correlation spectroscopy Radiofrequency... 

A MBER spectrometer is shown schematically in figure C1.3.1. The teclmique relies on using two inhomogeneous electric fields, the A and B fields, to focus the beam. Since the Stark effect is different for different rotational states, the A and B fields can be set up so that a particular rotational state (with a positive Stark effect) is focused onto the detector. In MBER spectroscopy, the molecular beam is irradiated with microwave or radiofrequency radiation in the... 

If the radiofrequency spectmm is due to emission of radiation between pairs of states - for example nuclear spin states in NMR spectroscopy - the width of a line is a consequence of the lifetime, t, of the upper, emitting state. The lifetime and the energy spread, AE, of the upper state are related through the uncertainty principle (see Equation 1.16) by... 

In NMR spectroscopy the precise energy differences between such nuclear magnetic states are of interest. To measure these differences, electromagnetic waves in the radiofrequency region (1-600 MHz) are applied, and the frequency at which transitions occur between the states, is measured. At resonance the condition... 

Radiofrequency spectroscopy (NMR) was introduced in 1946 [158,159]. The development of the NMR method over the last 30 years has been characterised by evolution in magnet design and cryotechnology, the introduction of computer-based operating systems and pulsed Fourier transform methods, which permit the performance of new types of experiment that control production, acquisition and processing of the experimental data. New pulse sequences, double-resonance techniques and gradient spectroscopy allow different experiments and have opened up the area of multidimensional NMR and NMRI. 

Main advances in ESR spectroscopy have recently come about by adding new dimensions to basic ID ESR [1015]. Dimensions such as time and radiofrequency radiation have either created new spectroscopies or enriched one-dimensional forms. Examples are pulsed ESR and ENDOR. 

Nuclear magnetic resonance spectroscopy Interaction magnetic fields - nuclei Resonance of radiation quanta, h v Radiofrequency pulses Spectrum in time or frequency (FT) domain ... 

Electron-nuclear double resonance (ENDOR) spectroscopy A magnetic resonance spectroscopic technique for the determination of hyperfine interactions between electrons and nuclear spins. There are two principal techniques. In continuous-wave ENDOR the intensity of an electron paramagnetic resonance signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR the radio frequency is applied as pulses and the EPR signal is detected as a spin-echo. In each case an enhancement of the EPR signal is observed when the radiofrequency is in resonance with the coupled nuclei. 

Most of us have encountered nuclear magnetic resonance (NMR) spectroscopy many times in the past, for example when analysing the products of preparative organic chemistry. In NMR spectroscopy, the nucleus of an atom is excited following absorption of a photon (in the radiofrequency region of the electromagnetic spectrum). 

Nuclear magnetic resonance (NMR) spectroscopy In NMR technique, a sample is placed in a magnetic field which forces the nuclei into alignment. When the sample is bombarded with radiowaves, they are absorbed by the nuclei. The nuclei topple out of alignment with the magnetic field. By measuring the specific radiofrequencies that are emitted by the nuclei and the rate at which the realignment occurs, the spectroscope can obtain the information on molecular structure. 

In passing it is interesting to note that Fig. 5 qualitatively explains the reason for the difference in the effect of motion on spectral lines in radiofrequency and optical spectroscopy. In radiofrequency spectroscopy one refers to motional narrowing, while collisional broadening is used to... 

The physical chemist of today has a wide variety of methods at his disposal for the experimental investigation of electronic structure and all of them have been used in attempts at obtaining evidence of the participation of outer d-orbitals in bonding. One such group of methods is constituted by the various techniques of radiofrequency spectroscopy, which have the advantage that they yield information about the molecule in its ground state. In this they have a distinct superiority over, say, electronic absorption spectra where it is necessary to consider both ground and excited states. Moreover much of the data derived from radiofrequency spectroscopic methods concerns essentially just one part of the molecule so that attention can be concentrated on those atoms of interest in whatever study happens to be under way. 

Almost all the parameters yielded by the various types of radiofrequency spectroscopy arise from the interaction of nuclear magnetic or electrostatic moments with the magnetic or electrostatic fields produced by the surrounding electrons. A consideration of the way these interactions arise shows that they fall into two groups one of the groups contains terms proportional to the electron density at the nucleus, N, itself, Vn(0), and consequently reflects only the s-character of the wave-function centered on N, v>n while the other is proportional to the value for all or some of the electrons surroimding the nucleus N (Table 1). This latter term vanishes for s-type orbitals and for p, d, f orbitals of the same principal quantum number has values in the order p > > d > > f. In practice this means that in a first approximation, only p-electrons contribute to and that the direct effect of the d-orbitals is only... 

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