Calculation of isotope enrichment using a unimolecular decomposition scheme for polyatomic molecules following infrared laser excition
✍ Scribed by K.C. Kim; J.M. McAfee
- Publisher
- Elsevier Science
- Year
- 1977
- Tongue
- English
- Weight
- 558 KB
- Volume
- 45
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
A mechanism is proposed to account for laser-induced isotope enrichment reactions which proceed by unimolecular dissociation following selective vibrational excitation. Assuming that the internal vibrational energy relaxation is not colq!ete during the molecular dissociative lifetime, both selective single and multiphoton absorption mechanisms were investigated. Successful experimental results for isotope emichment of sulfur, boron, chlorine, etc., have been reported recently using a carbon dioxide laser. The enrichment process has been loosely explained by a mechanism based on multiphoton absorption of the infrared radiation to the dissociation limit [ 1,2] . Additionally, a dissociative electron attachment mechanism has been postulated in the case of SF, [3] _ The multiphoton absorption scheme suffers from a vibrational energy defect of the ground state resonant energy due to the anharmonic nature of excited vibrational levels which tends to present serious problems near the dissociation limit. However, the anharmonicity effect is counterbalanced by the increased density of states at higher energies, but any argument based on high densities of states assumes virtually continuous energy states. The second explanation of dissociative electron attachment depends on the relatively high cross section for electron attachment of the SF6 molecule, and requires a relatively abundant source of electrons to initiate the reaction. This mechanism has some merit in explaining the experimental results on SF6, but needs further investigation since isotope enrichment of other molecules may not be explained by a similar mechanism. * Work performed under the auspices of the US_ Energy Research and Development Administration_