Line width transit time broadening

The problem of transit-time broadening was recognized many years ago in electric or magnetic resonance spectroscopy in molecular beams [1253]. In these Rabi experiments [1254], the natural linewidth of the radio frequency or microwave transitions is extremely small because the spontaneous transition probability is, according to Vol. 1, (2.22), proportional to co. The spectral widths of the microwave or RF lines are therefore determined mainly by the transit time AT = d/v of molecules with the mean velocity v through the interaction zone in the C field (Fig. 5.10a) with length d. 

Even if such high power levels cannot be sustained, it should still be possible to observe two-photon excitation with the help of more sensitive detection methods. Towards this end, U. Boesl and E. Hildum in our laboratory have recently completed construction of a hydrogen atomic beam apparatus, which permits the detection of 2S atoms via photoionization. The resulting charged particles are observed with a time-of flight mass spectrometer. Despite transit time broadening and uncompensated relativistic second order Doppler shifts, we hope to achieve line widths on the order of 1 Mhz in this... 

It is much more difficult to observe the Mossbauer effect with the 130 keV transition than with the 99 keV transition because of the relatively high transition energy and the low transition probability of 130 keV transition, and thus the small cross section for resonance absorption. Therefore, most of the Mossbauer work with Pt, published so far, has been performed using the 99 keV transition. Unfortunately, its line width is about five times larger than that of the 130 keV transition, and hyperfine interactions in most cases are poorly resolved. However, isomer shifts in the order of one-tenth of the line width and magnetic dipole interaction, which manifests itself only in line broadening, may be extracted reliably from Pt (99 keV) spectra. 

B. Experimental Line Widths for Ln + and An + Transitions. The first detailed quantitative study of the temperature dependence of the line width in a lanthanide system was done on Pr + in LaF3 by Yen, Scott, and Shawlow (43). Since that time line widths as low as 15 kHz have been observed for the D2 to 4 transition of Pr + in LaF2 at 2 K (44). To observe such narrow homogeneous line widths within the strain broadened inhomogeneous line width found in solid systems, experimental techniques involving tunable dye lasers are usually employed. These techniques have been reviewed by Selzer (45) while specific results for the lanthanide systems have been reviewed by Yen (46). ... 

The decision as to which metal to choose for a particular experiment is also dictated by the fact that, in addition to shift changes, all of the lanthanides produce some change in the nuclear relaxation-times of the substrate, and thereby increase the line-widths of the n.m.r. transitions. The ratio of shift change to line broadening is optimal for such metals as europium (III) and praseodymium (III), which are, therefore, the most suitable for use as shift reagents. In contrast, gadolinium (III) is totally unsuited for this particular purpose, as it induces substantial... 

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