Quadrupole line

We have limited our investigations to the action of gamma-rays and fast neutrons on aromatic, alicyclic, aliphatic, and ionic compounds. The absorption coefficients for these types of radiation have an order of magnitude of lO /cm which is particularly adequate. Shallow penetrating radiations would only alter the superficial layers and would obviously not be able to affect the intensity of the quadrupole line substantially. This is for instance the case for ultraviolet light which has been shown to be unable to produce any effect on the resonance line of iodoform (CHI3 3Sg)... 

MHz relative to the protons in Mc4Si at exactly 100 MHz. The effect of quadrupole line broadening is attenuated to some extent by the magnitude of / (/= 9/2), and the line widths are among the narrowest of all quadrupolar nuclei studied to date. One would expect efficient relaxation via the quadrupole moment, giving very short T2 times and consequently broad NMR signals. Also if the electronic distribution around the nucleus is symmetrical, sharp resonances can be obtained. 

Fig. 3.41. The spectra of van der Waals molecules containing D2 that are centered at the D2 Si(0) rotovibrational transition frequency after [267], Bottom (D2>2 first trace above bottom trace D2Ne second trace above bottom trace D2Ar top D2Kr. A sharp monomer quadrupole line can also be seen in each trace at the position of the D2 Si(0) transition frequency.

The tetrahedral environment around nickel in [Ni(PF3)4] makes the electrical field gradient tensor zero and its 61Ni NMR spectrum shown in Fig. 1 exhibits minimum quadrupole line broadening. Both the directly bounded 61Ni-31P coupling ( J p = 482 Hz) and the two-bond 61Ni-19F coupling (2e/NiF = 28 Hz) have been recorded (129). 

The N.Q.R. spectra of 35ci in chloral hydrate and chloral deuterate have been recorded in the temperature range 77 to 323°K. 17,18,19,20 (Similar spectra of Cl have also been recorded 20). The frequencies of the quadrupole lines obtained by independent workers 17,1952 ... 

A1 sites of the framework (Fig. 11). However, if the nonframework A1 exists as polymeric aluminum oxides or oxide hydrates in the zeolite pores, strong quadrupole line broadening may be observed owing to heavy distortions of the octahedral symmetry of the AlO sites. 

An important application of Al MAS NMR is the detection and characterization of nonframework aluminum species formed by various thermal or hydrothermal treatments of zeolites, as is usually applied in the dealumination processes or the preparation of the acidic H-forms of zeolites. Provided that all aluminum is visible in the spectrum, such that no signal intensity is lost as a result of very strong quadrupole line broadening, the relative proportions of framework and nonframework A1 in zeolites can be directly determined from the intensities of the signals at about 60 and Oppm. 

Many other atoms possess metastable levels, e.g. mercury and the inert gases. In gas discharges these play an important role since the population in the metastable levels can be very high and these atoms are more easily ionized than atoms in the ground state. However, forbidden magnetic dipole and electric quadrupole lines are difficult to observe in the spectra of laboratory sources since they are extremely weak in comparison with the allowed electric dipole transitions. Also, the metastable atoms are often quenched by collisions with other atoms or with the walls of the discharge tube before radiation can occur. By contrast, in the upper atmosphere, the solar corona, and in gaseous nebulae the densities of atoms are so low that collision pro-... 

Transition probabilities of forbidden lines. Accurate theoretical calculations of the transition probabilities of forbidden lines can be made without great difficulty for those lines which satisfy all the selection rules in Table 7.1. However, there are many cases of magnetic dipole or electric quadrupole lines where one or more of the approximate rules is broken. In these cases the atomic wave-functions must be calculated in intermediate coupling and the resulting transition probabilities are consequently less reliable. 

End views of the quadrupole assembly (a) showing the theoretically desired cross-section and (b) illustrating the practical system. In (b), a positive potential, +(U + Vcoscot), is applied to two opposed rods (A) and a negative potential, -(U + Vcoscot), to the other two (B). The dotted lines indicate planes of zero electric field. The dimension (r) is typically about 5 mm with rod diameters of 12 mm. The x- and y-axes are indicated, with the z-axis being perpendicular to the plane of the paper. 

For a line OB (Figure 25.4) of smaller slope (smaller a/q or smaller U/V), an even greater range of m/z values will be transmitted through the quadrupole assembly. Conversely, for a line OC that passes through the apex (r) of the region of stability, no ions of any m/z value are transmitted. 

Ions of different m/z values pass sequentially in time through the quadrupole mass filter to reach an in-line, single-point ion collector. 

Nuclear electric quadrupole QCC (quadrupole coupling constant), (asymmetry parameter) Line-shape analysis, nutation NMR Coordination symmetry... 

Heterogeneous polymerization, 163 Hexachlorobenzene, influence of radiation on, 198, 200 quadrupole spectrum, 197 Hexachlorocyclohexane resonance lines, 191... 

In presence of molecular motion the NMR line shape will change. A particularly simple situation arises, if the motion is rapid on timescale defined by the inverse width of the spectrum in absence of motion 6 1. In this fast exchange limit, which in 2H NMR is reached for correlation times tc < 1CT7 s, the motion leads to a partially averaged quadrupole coupling and valuable information about the type of motion can directly be obtained from analysis of the resulting line shapes. The NMR frequency is then given by... 

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