Molecular laser isotope separation process

Molecular hydrogen, 23 759 Molecular imprinting, 6 397 Molecular interactions, 25 103 Molecular interaction theories, 24 38 Molecular Laser Isotope Separation (MLIS) process, 25 416 417 Molecular level machine, 2 7 58 Molecularly imprinted plastics (MIPs) smart, 22 717)... 

The invention of lasers in the early 1960s made possible the laser isotope separation (LIS) approach. The first US research began in the 1960s at the Los Alamos National Laboratory (LANL) lasers were used to excite the U molecules in a UFj stream, a process they called molecular laser isotope separation (MLIS). Their work continued for a decade or more. 

The dramatic growth occurring over the past few years in laser chemistry and laser isotope separation has refocused interests upon dissociative processes in molecules. Collectively, these interests are traceable to the pragmatic goals of producing appreciable populations of selected atomic or molecular states having useful reactive properties or isotopic content. From this perspective, it is natural that photodissociation of some parent molecule would appear to be the ideal means for obtaining a desired product. 

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]. 

However, it is important to recognize that the first few steps in the absorption process are selective. Owing to the low density of states in this region, only one molecular species (which has a transition resonant with the laser frequency) in a mixmre of other molecules will absorb and thus be selectively excited into the quasicontinuum and on to the dissociation limit. Indeed, it is possible to achieve isotope separation using IR multiple-photon excitation for example, can be selec-... 

The Energy Research and Development Agency (ERDA), the forerunner to the DOE, through the late 1970s to 1981 supported the study of three new experimental processes for uranium enrichment. Two were based upon laser separation, and one on plasma separation. Jersey Nuclear-Avco Isotopes Incorporated (subsidiary of Exxon) and the LLNL worked on atomic uranium vapor. LLNL referred to it as AVUS. The LANL and a group at Exxon Research Laboratories (not connected with Jersey-Avco) worked on molecular UFg. TRW Incorporated pursued research work on a plasma separation process. Union Carbide Nuclear Division (UCC-ND) supported each in their efforts. In 1981, the AVLIS process at LLNL was selected as the process to be developed further and the other processes were subsequently phased out. 

Upon the closure of AVLIS, the only remaining laser process on the world stage was (separation of isotopes by laser excitation [SILEX]), a molecular separation process developed by the Australian company Silex Systems Limited. The French had ceased work on their laser program, SILVA, in 2003. 

In the previous chapter we have seen how tunable lasers can be used in a multitude of ways to gain basic information on atomic and molecular systems. Thus, the laser has had a considerable impact on basic research, and its utility within the applied spectroscopic field is not smaller. We shall here discuss some applications of considerable interest. Previously, we have mainly chosen atomic spectroscopic examples rather than molecular ones, but in this chapter we shall mainly discuss applied molecular spectroscopy. First we will describe diagnostics of combustion processes and then discuss atmospheric monitoring by laser techniques. Different aspects of laser-induced fluorescence in liquids and solids will be considered with examples from the environmental, industrial and medical fields. We will also describe laser-induced chemical processes and isotope separation with lasers. Finally, spectroscopic aspects of lasers in medicine will be discussed. Applied aspects of laser spectroscopy have been covered in [10.1,2]. 

J.L. Lyman Laser-induced molecular dissociation. Applications in isotope separation and related processes, in [Ref.l0.1,p.417]... 

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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