Weak Magnetic Fields

At very weak fields, it is sometimes possible to observe an increase in the rate of S-T mixing, which in Fig. 8.6 corresponds to an increase in geminate product yield. This is known as a low-field effect (LFE) and has been a topic of interest recently due to the interest in the effect of environmental electromagnetic fields on human health and 

FIGURE 8.7 The zero-field wavefunctions of the eight spin states of a one-proton RP and the dependence of their energy on the strength of an applied magnetic field. 

MAGNETIC FIELD EFFECTS ON RADICAL PAIRS IN HOMOGENEOUS SOLUTION 

There have been a number of observations of the LFE in systems where the RP hfetime has been extended through the use of RIPs or microreactors (summarized in a recent review). Of interest for neutral RPs in solution reactions is the hyperfine dependence of these LFEs. Early experimental and theoretical studies concluded that substantial LFEs are only observed for RPs in which there are substantial HFCs in one pair member and negligible couplings in the other. In a more recent study, RPs with a wide range of combinations of HFCs and lifetime were screened for LFEs by simulation on a supercomputer. This study concluded that indeed for short-lived RPs, the large small HFC combination is required to produce substantial LFEs, but for long-hved RPs the restriction vanishes. 

FIGURE 8.8 Magnetic field dependence for the photolysis of a series of benzoyl containing molecules in cyclohexanol solution obtained by time-resolved infrared spectroscopy of the carbonyl group of the resulting benzoyl radical. Key 1 = a,a,a-trimethylacetophenone, 2 = 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone, 3 = 1-benzoylcyclohexanol, 4 = 2-hydroxy-2-methy Ipropiophenone, 5 = benzoin, 6 = methyl ether benzoin, 7 = dimethyl ether benzoin, 8 = 2-dimethylamino-2-(4-methyl-benzyl)-l-(4-morpholin-4-yl-phenyl)-butan-l-one. 

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Another example of systems where the pattern formation is observed is a two-dimensional electron liquid in a weak magnetic field with partially filled upper Landau levels. In such systems the uniform distribution of the charge density at the upper Landau level is unstable against the formation of a charge density... 

One device is made up of samples of superconducting materials put inside a transformer a low-frequency small current in the primary creates a weak magnetic field. 

To increase the ionization probability, a homogeneous weak magnetic field is used to keep the electrons on a spiral path. At the end of the ionization chamber, electrons are collected in a positively charged trap, where the electron current is measured and kept constant by the emission regulator circuitry. 

One other 1-electron density is of great imprortance - the current density J(r), which is again a pseudovector density. This is everywhere zero until we apply an infinitely weak magnetic field, so as to define a quantization axis and to introduce an imaginary term in the wavefunction i. The usual kinetic energy operator in the Hamiltonian is then replaced by... 

In the weak magnetic field region (0.6 T), the experimental results are not in agreement with the intrinsic pinning model. In this case, the flux pinning at the film surface becomes more dominant than the intrinsic pinning by the ab planes. 

In order to obtain the spatial distribution of the spins, i.e. NMR imaging (MRI), in a sample of interest, weak magnetic field gradients, G, are additionally superimposed to localize the spins. As a result, the NMR signal contains spatial information. The resonance frequency along the sample corresponding to... 

The simplest case is that of an unfocused ion beam entering a weak magnetic field in the X-Y plane. This corresponds to a minimum magnitude of cross magnetic fields generated by unworked 304 stainless steel cell... 

For a weak magnetic field the resulting small deflection d can be approximated by... 

Abstract The effect of a weak magnetic field with B0<1 T on photoconductivity of the... 

It is rather likely that understanding of the anisotropic distribution of the angular momenta of atoms was enhanced by Hanle s [184] discovery in 1924. Hanle observed the effect of the disappearance of linear polarization in fluorescence in a weak magnetic field directed at right angles to the E-... 

Watanabe, H. and Tsuchlya, S. (1983). Quantum beats in the fluorescence of jet-cooled SO2 under a weak magnetic field, J. Phys. Chem., 87, 906-908. 

Wood, R.W. and Ellet, A. (1924). Polarized resonance radiation in weak magnetic field, Phys. Rev., 24, 243-254. 

Note the resemblance of the fluorine atom absorption to the symmetry of the absorptions of the magnetic nonequivalent aromatic protons described in Section 3.9. The complexity in all of these spectra is not a result of an inadequate magnetic field. In fact, a more powerful magnetic field would result in greater complexity. This is quite different from the response of a first-order system, which may not be resolved in a weak magnetic field, but would show a first-order spectrum at a sufficiently high field. 

RADIATIVE CONDUCTIVITY OF C(> SINGLE CRYSTAL IN WEAK MAGNETIC FIELD... 

Fullerenes and their chemical compounds are perspective materials for application in nanotechnology, spintronics and single-electronics [1], Thus, the search of ways of high-speed, contactless, selective control of electron-optical properties of fullerene-based materials is actual problem. It is well known, that weak magnetic field (MF) with induction B < IT effectively influences electron-optical properties of some organic compounds (for instance, anthracene, tetracene, etc.) [2]. 

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