Atomic beam magnetic resonance structure

Hyperfine structure measurements using on-line atomic-beam techniques are of great importance in the systematic study of spins and moments of nuclei far from beta-stability. We will discuss the atomic-beam magnetic resonance (ABMR) method, and laser spectroscopy methods based on crossed-beam geometry with a collimated thermal atomic-beam and collinear geometry with a fast atomic-beam. Selected results from the extensive measurements at the ISOLDE facility at CERN will be presented. 

Thermal atomic beams have been used extensively to determine nuclear spins and moments by investigations of the atomic hyperfine structure. The atomic-beam magnetic resonance (ABMR) method has already become classical [2]. More recent efforts include laser spectroscopy in a crossed-beam geometry, in which a large supression of the Doppler width is obtained by collimation of the atomic beam. 

Millimeter wave spectroscopy with a free space cell such as a Broida oven is more sensitive than lower frequency microwave spectroscopy. However, the higher J transitions monitored by millimeter wave spectroscopy often do not show the effects of hyperfine structure. In the case of CaOH and SrOH, the proton hyperfine structure was measured in beautiful pump-probe microwave optical double resonance experiments in the Steimle group [24,68], They adapted the classic atomic beam magnetic resonance experiments to work with a pulsed laser vaporization source and replaced the microwave fields in the A and C regions by optical fields (Fig. 15). These sensitive, high-precision measurements yielded a very small value for the proton Fermi contact parameter (bF), consistent with ionic bonding and a... 

W. Ertmer, B. Hofer, Zeiofield hyperfine structure measurements of the metastable states 3d 4s F3/29/2 of SC using laser-fluorescence-atomic beam magnetic resonance technique. Z. Phys. A 276,9 (1976)... 

W. Zeiske, G. Meisel, H. Gebauer, B. Hofer, W. Ertmer Hyperfine structure of cw dye-laser populated high lying levels of Sc by atomic-beam magnetic-resonance. Phys. Lett. 55A, 405 (1976)... 

Protein structure The three-dimensional structure of a protein can be determined almost to the determination atomic level by the techniques of X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy. In X-ray crystallography a crystal of the protein to be visualized is exposed to a beam of X-rays and the resulting diffraction pattern caused as the X-rays encounter the protein crystal is recorded on photographic film. The intensities of the diffraction maxima (the darkness of the spots on the film) are then used to mathematically construct the three-dimensional image of the protein crystal. NMR spectroscopy can be used to determine the three-dimensional structures of small (up to approximately 30 kDa) proteins in aqueous solution. 

As beautiful as this suggestion might be, significantly more must be done to confirm it than to observe that the combination of sixty carbon atoms can be produced in greater abundance than other numbers. Unfortunately, the laser vaporization supersonic cluster beam technique does not produce enough material to perform direct structural techniques like x-ray crystallography or even indirect (but often decisive) experiments such as infrared or Raman spectroscopy, or nuclear magnetic resonance. 

All measurements were made in the gas phase. The methods used are abbreviated as follows. UV ultraviolet (including visible) spectroscopy IR infrared spectroscopy R Raman spectroscopy MW microwave spectroscopy ED electron diffraction NMR nuclear magnetic resonance LMR laser magnetic resonance EPR electron paramagnetic resonance MBE molecular beam electric resonance. If two methods were used jointly for structure determination, they are listed together, as (ED, MW). If the numerical values listed refer to the equilibrium values, they are specified by and 6. In other cases the listed values represent various average values in vibrational states it is frequently the case that they represent the Tj structure derived from several isotopic species for MW or the r structure (i.e., the average internuclear distances at thermal equilibrium) for ED. These internuclear distances for the same atom pair with different definitions may sometimes differ as much... 

Information relevant to the electronic configuration can be obtained from atomic emission spectroscopy, x-ray photoelectron spectroscopy, paramagnetic susceptibility measurements, electron paramagnetic resonance, electronic transition spectroscopy, crystal structure data, and atomic-beam experiments. Discussions of the theoretical and experimental aspects of atomic spectroscopy, magnetic properties, crystal structures of solids, and electronic absorption spectroscopy are to be found in the later chapters of this work. 

Techniques such as ray-based techniques and nuclear magnetic resonance (NMR) can be used for the structural characterization of metallomes and metalloproteome. Ray-based techniques can characterize the structure at the atomic level. Rays that can be used for structural analysis include X-rays, gamma rays, or neutron beams. 

These atoms will not be refocussed at the detector in this so-called flop-out arrangement of the polarizer and analyser fields. Consequently when the detector current is recorded as a function of oJq for a fixed value of B, a series of sharply defined minima will be observed. The width of these magnetic resonance lines is often as narrow as 300 Hz and permits very precise measurements of the spins and magnetic moments of both atoms and nuclei. We shall now discuss some aspects of the atomic beam apparatus in more detail before considering the application of this technique to hyperfine structure measurements in one-electron atoms. 

The ideas embodied in Eq. (1) were well established long before magnetic resonance experiments were carried out, from the famous Stern-Gerlach experiment, in which a beam of silver atoms was found to split into two separate beams upon passage through an inhomogeneous magnetic field. This was a direct reflection of the two only possible spin states of the unpaired electron within the atom. The existence of fine structure in atomic spectra provided further evidence for electron spin. 

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