Radiofrequency fine structure

Pulse radiolysis systems capable of picosecond time resolution use the fine structure of the output from the electron linear accelerator. Electrons in the accelerating tube respond to positive or negative electric field of the radiofrequency, and they are eventually bunched at the correct phase of the radiofrequency. Thus the electron pulse contains a train of bunches or fine structures with their repetition rate being dependent on the frequency of the radiofrequency (350 ps for the S-band and 770 ps for the L-band). 

Abbreviations BCC. body centered cubic DOS. density of states ESR. electron spin resonance HX.AI S, extended X-ray absorption fine structure F CC. face centered cubic (a crystal structure). FID, free induction decay FT, Fourier transform FWHM, full width at half maximum HCP, hexagonal close packed HOMO, highest occupied molecular orbital IR, Infrared or infrared spectroscopy LDOS, local density of states LUMO, lowest unoccupied molecular orbital MAS. magic angle spinning NMR. nuclear magnetic resonance PVP. poly(vinyl pyrrolidone) RF. Radiofrequency RT, room temperature SEDOR, spin echo double resonance Sf, sedor fraction SMSI, strong metal-support interaction TEM. transmission electron microscopy TOSS, total suppression of sidebands. 

For radiofrequency measurements of the fine structure of hydrogen, on the other hand, the Doppler effect is completely tmimportant, since it is proportional to the frequency which is actually measured. The fine structure intervals are given by frequency differences in optical spectroscopy in radiofrequency spectroscopy they are measured directly. The greater precision of radiofrequency measurements would compel careful investigation of the conditions in a gas discharge if this method were chosen for the excitation of the atoms. In fact, in the radio-frequency experiments which have so far been performed on hydrogen and ionized helium, the method of excitation by electron bombardment has been used. 

Between the A and B regions, a radiofrequency field was applied to induce fine-structure transitions within the v" = 1 level of the ground electronic state, split by the nuclear hyperfine interaction. The selection rnles for these transitions, which ranged in frequency from 360 to 7700 MHz, were A7 = 1, AF = 0, 1. They were detected through resonant changes in the fluorescence intensity an example of a radiofrequency double resonance line is shown in frgnre 11.53. The observed spectrum involved N values from 1 to 27. 

With the envisioned higher resolution, it should be possible to determine a better value of the electron/proton mass ratio from a precise measurement of the isotope shift. And a measurement of the absolute frequency or wavelength should provide a new value of the Rydberg constant with an accuracy up to 1 part in 10, as limited by uncertainties in the fine structure constant and the mean square radius of the proton charge distribution. A comparison with one of the Balmer transitions, or with a transition to or between Rydberg states could provide a value for the IS Lamb shift that exceeds the accuracy of the best radiofrequency measurements of the n=2 Lamb shift. Such experiments can clearly provide very stringent tests of quantum electrodynamic calculations, and when pushed to their limits, they may well lead to some surprising fundamental discovery. 

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