Quadrupolar momentum

In a rotating molecule containing one quadrupolar nucleus there is an interaction between the angular momentum J of the molecule and the nuclear spin momentum I. The operator of this interaction can be written as a scalar product of two irreducible tensor operators of second rank. The first tensor operator describes the nuclear quadrupole moment and the second describes the electrical field gradient at the position of the nucleus under investigation. 

Abstract Recent advances in nuclear magnetic resonance spectroscopy of quadrupolar (/> 1/2) nuclei with half-integer spins in solids have been reviewed. The advent of multiple-quantum (MQ) magic-angle spinning (MAS) spectroscopy gave new momentum to the study of quadrupolar nuclei in materials of academic and industrial interest such as min-... 

When Qc or Q2 is operated as a linear ion trap, an rf drive voltage of 1 MHz is applied. An auxiliary ac potential is applied in quadrupolar fashion to the rod arrays of either Qc or Q2 so as to excite ions at secular frequencies. Ions are trapped radially in the linear ion trap Qc by the rf potential, and are confined axially within the rod array by dc potentials applied to the aperture plates, IQ2 and IQ3. Thus, a linear ion trap resembles a bathtub having a parabolic cross-section and near vertical ends. Ions enter the linear ion trap close to the zero-field centerline of the device and encounter a series of momentum-dissipating collisions with collision gas. 

According to the dipole selection rules, photoexcitation of a core electron with angular momentum I probes the I 1 components of the final state. In the Lm absorption processes I — 1 transitions (2p - 6s) can be neglected. Their probability is less than 3% of the / -I-1 (2p - 5d) transition probability (cf., e.g., Barinski and Nefedow 1969). The contribution of quadrupolar transitions to the absorption coefficient can also be neglected. Quadrupolar transitions turn out to be important only in the higher Z elements (in Lnm absorption for Z > 70). Calculated ratios of quadrupolar to dipole transitions for K and L absorption are given in table 2 (Muller and Wilkins 1984). 

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