Photochemical isotope separation processes

For many years attempts have been made to use photochemical processes for the separation of Isotopes. The basic idea is to utilize the difference in the absorption spectra of different isotopic species, and by use of sufficiently monochromatic light of an appropriate wavelength to excite only one of the species to an upper energy level. The excited species may then be separated by chemical or physical means from its isotopic partners the separating process need not have any Inherent isotopic selectivity. A particularly successful application of the method was to the separation of Hg isotopes by Gunning et al. (36,37). For example. 

ACS Symposium Series American Chemical Society Washington, DC, 1975. 

The essential requirements for any photochemical isotope separation scheme follow  

Absorption spectrum with a well resolved isotope shift (vibrational-rotational or vlbronic for molecules, electronic for atoms) 

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Our examination of the photochemical literature of uranium clearly shows that extensive attention has been given to UFg, while other compounds, until recently, have been almost ignored. The attention given to UFg, of course, relates back to the great interest in achieving a low cost laser induced isotope separation process for uranium isotopes. The economics of isotope separation, which have been briefly discussed by Letokhov and Moore (61), have consequently dictated the direction of much of the applied photochemical research on uranium compounds. Nonetheless, from the existing spectroscopic and photochemical data outlined here it would be expected that coordination and... 

In this paper a number of isotope separating processes will be examined, particularly those utilized on a large Industrial scale, and the bases for the above conclusions will be presented. Finally, the fundamental principles of a photochemical method of Isotope separation based upon excitation by laser light, which has excited a great deal of current Interest, will be outlined. 

Selective excitation of wavepackets with ultrashort broadband laser pulses is of fundamental importance for a variety of processes, such as the coherent control of photochemical reactions [36-39] or isotope separation [40--42]. It can also be used to actively control the molecular dynamics in a dissipative environment if the excitation process is much faster than relaxation. For practical applications it is desirable to establish an efficient method that allows one to increase the target product yield by using short laser pulses of moderate intensity before relaxation occurs [38]. 

Laser radiation is monochromatic and in many cases it also is tuneable these two characteristics together provide the basis for high-resolution laser spectroscopy. The interaction between laser radiation and molecules can be very selective (individual quantum states can be selected), permitting chemists to investigate whether energy in a particular type of molecular motion or excitation can influence its reactivity. Photochemical processes can be carried out with sufficient control that one can separate isotopes, or even write fine fines (of molecular dimensions) on surfaces. 

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