Doppler broadening reduction

A remarkable feature of these spectra is the resolution of individual rotational lines in such large molecules. [Note that the expanded specttum in, for example. Figure 9.47(a) covers only 5000 MFIz (0.17 cm )]. This is due partly to the very low rotational temperature (3.0 K for aniline and 2.2 K for aniline Ar), partly to the reduction of the Doppler broadening and partly to the very high resolution of the ring dye laser used. 

Even in a molecule the size of benzene the resolution achieved in this way is sufficient to investigate the dynamic behavior of individual rotational states. For this it is necessary to eliminate the Doppler broadening of the rovibronic transitions. Two methods have been applied (i) the elimination of Doppler broadening in a Doppler-free two-photon-transition and (ii) the reduction of Doppler broadening in a molecular beam. Measurements of the dynamic behavior have been performed in the frequency [3] and time domain [4]. We will briefly summarize the results from high-resolution measurements and discuss the conclusions on the intramolecular decay mechanism. Then it will be discussed how the intramolecular dynamics is influenced by the attachment of an Ar or Kr atom to the benzene molecule, leading to a weakly bound van der Waals complex. 

Doppler broadening of the emission lines will be much reduced. The same principle for line width reduction is used in absorption measurements, in which absorption from a continuous wavelength distribution by atoms is recorded at right angles to the collimated beam. The resulting Doppler width when atoms with a preferred direction of motion are used can be calculated in a similar way as for the case with evenly distributed directions of motion. In practical cases, linewidths of tens of MHz are obtained in optical absorption measurements on atomic beams at thermal velocities (a few hundred m/s). 

J.O. Stoner, J.A. Leavitt Reduction in Doppler broadening of spectral lines in fast-beam spectroscopy. Appl. Phys. Lett. 18, 477 (1971)... 

Eliminating from the reactor prevents the production of more Pu and accelerates plutonium destruction. A major disadvantage of removing jg, e reduction or elimination of a prompt negative Doppler reactivity coefficient. As the plutonium fuel temperature ri.ses, the plu< tonium fission resonances broaden increasing the core reactivity. Without adequate control, this can lead to even higher fuel temperatures and cause a reactor accident. In addition, the delayed neutron fraction for - Pu (0.0022) is much smaller than that of (0.0069). This also makes a pure plutonium reactor more difficult to control. Removal of eliminates the primary reactivity holddown mechanism in LWRs. 

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