Turning quadrupole

The interaction energy depends on Gn, and v and the allowed energy levels turn out to depend on eQ q. Division by h gives eqQ jh which we refer to as the quadrupole coupling constant (QCC). 

Once available, and supplemented by the nuclear contribution, the EFG tensor can be diagonalized. The numerically largest element (in atomic units) defines the value of q which is in turn used to calculate the quadrupole splitting parameter... 

Besides a strongly coupled proton with a nearly isotropic hfc of Ah —20 MHz, two clearly separated nitrogen peaks between 15-26 MHz with unresolved quadrupole and nuclear Zeeman splittings have been observed along all three turning points of the g tensor (Fig. 39b). In the evaluation of the hf data collected in Table 12.1 it is assumed that the two metal-coordinated 14N exhibit roughly axial hfs tensors with the Ajj1 values oriented approximately perpendicular to each other. 

The resolving power of a quadrupole mass filter depends on the number of cycles experienced by an ion within the rf field, which in turn depends on its velocity. Thus, the resolution will increase with increasing mass, as ions of higher mass have lower velocity. However, the transmission efficiency will decrease, due to the longer time ions of higher masses spend in the quadrupole. 

Ion trajectory simulations allow for the visualization of the ion motions while travelling through a quadrupole mass analyzer (Fig. 4.36). Furthermore, the optimum number of oscillations to achieve a certain level of performance can be determined. It turns out that best performance is obtained when ions of about 10 eV kinetic energy undergo a hundred oscillations. [110]... 

Theoretically, each electrode should have a hyperbolic cross section for optimized geometry of the resulting quadrupole field, and thus for optimized performance. [103,104] However, cyclindrical rods are often employed instead, for ease of manufacture. By adjusting the radius of the rods carefully (r = 1.1468ro), a hyperbolic field may be approximated. [113] However, even slight distortions of the ideal quadrupole field either from interference with external fields or due to low mechanical precision or inadequate shape of the device cause severe losses of transmission and resolution. [114] The expected advantages of hyperbolic rods [115] have been demonstrated by ion trajectory calculations [110,116] circular rods cause a reduction in macromotion frequency because of an increased residence time of the ions in close vicinity to the rods this in turn means reduced resolution. 

Turning now to lithium, we have two nuclides available for NMR measurements Li and Li. Both are quadrupolar nuclei with spin quantum number / of 1 and 3/2, respectively. The natural abundance of Li (92.6%) provides enough NMR sensitivity for direct measurements, but also Li (7.4%) can easily be observed without enrichment. However, isotopic enrichment poses no practical problem and is advantageous if sensitivity is important, as for measurements of spin-spin coupling constants in solution and of quadrupole coupling constants in the sohd state. 

An important induced dipole component of pairs involving molecules is multipolar induction. Specifically, the lowest-order multipole consistent with the symmetry of H2 is the electric quadrupole. Each H2 molecule may be thought of as being surrounded by an electric field of quadrupolar symmetry that rotates with the molecule.-In that field, a collisional partner X is polarized, thus giving rise to an induced dipole moment which in turn is capable of emitting and absorbing light. For like pairs, molecule 1 will induce a dipole in molecule 2 and 2 will induce one in 1. In... 

H2-X where X is a molecule. If a molecule other than H2 is chosen as the collision al partner X, new absorption bands appear at the rotovi-brational bands of that molecule. As an example, Fig. 3.17 shows the rototranslational enhancement spectra [46] of H2-CH4 for the temperature of 195 K. At the higher frequencies (v > 250 cm-1), these look much like the H2-Ar spectrum of Fig. 3.10 the H2 So(J) lines at 354, 587, and 815 cm-1 are clearly discernible. Besides these H2 rotational lines, a strong low-frequency spectrum is apparent which corresponds to the (unresolved) induced rotational transitions of the CH4 molecule these in turn look like the envelope of the rotational spectra seen in pure methane, Fig. 3.22. This is evident in the decomposition of the spectrum, Fig. 3.17, into its main components [46] the CH4 octopole (dashed curve) and hex-adecapole (dot-dashed curve) components that resemble the CH4-CH4 spectrum of Fig. 3.22, and the H2 quadrupole-induced component (dotted curve) which resembles the H2-Ar spectrum, Fig. 3.14. The superposition (heavy curve) models the measurement (big dots) closely. Similar spectra are known for systems like H2-N2 [58]. 

In the experiment, a bare Pd surface was exposed to oxygen, until the surface attained a saturation coverage of O(s) of 0glt=O.4. The oxygen source was then turned off, and the surface was exposed to a constant flux of CO of Fco beginning at time t = 0 s. A quadrupole mass spectrometer was used to monitor the flux of the oxidation product C02, as well as CO, from the surface. The coverages of O(s) and CO(s) were deduced as a function of time through analysis of the data and the surface reaction mechanism above. 

This is just what has been done with Ag2. A sputtering source followed by a phase-space compressor chamber provided a beam of cooled negative cluster ions of many sizes. From these, the dimers were selected, accumulated in a quadrupole trap, and photodetached with a femtosecond, titanium-sapphire laser. After photodetachment by a 60-fs pulse, the neutral dimers oscillate, causing corresponding oscillations in the ionization cross section, in turn generating the oscillations that dominate the intensity pattern in Fig. 11. This is a simple phenomenon, yielding in a simple way the... 

March, R. E. (2000b). Quadrupole ion trap mass spectrometry. A view at the turn of the century. Int. J. Mass Spectrom. 200 285-312. 

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