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Isotope effects in mass-spectrometry; Les effets isotopiques en spectrometrie de masse

Abstract

In the first part, a review is made of the work concerning the influence of isotopic substitution on the stabilities of ionised molecules and the bond-breaking probabilities; metastable transitions are also affected by this substitution. A model based on the Franck-Condon principle accounts for the experimentally observed isotopic effects for diatomic molecules; to a certain extent it is possible to generalise the calculation for the case of isotopic molecules of carbon dioxide gas. For deuterated polyatomic molecules there exist a {pi} effect making it possible to compare the relative stabilities of the X-H and X-D bonds, and a {gamma} effect which characterizes the different behaviours of the X-H bond in a normal molecule and in its partially deuterated homologue. Usually there is a very marked {pi} effect (e.g. the C-D bonds are more difficult to break than the homologous C-H bonds) and a {gamma} effect, the partial deuteration of a molecule leading in general to an increase in the probability of breakage of a given bond. An interpretation of {pi} and {gamma} effects based on Rosenstock near-equilibrium theory accounts for the observed phenomena, qualitatively at least, in the case of propane and acetylene. In the second part are gathered together  More>>
Authors:
Leicknam, J P [1] 
  1. Commissariat a l'Energie Atomique, Saclay (France). Centre d'Etudes Nucleaires. Departement de physico-chimie, service des isotopes stables, section de spectrometrie de masse
Publication Date:
May 01, 1967
Product Type:
Thesis/Dissertation
Report Number:
CEA-R-3134
Resource Relation:
Other Information: 111 refs
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACETYLENE; CHEMICAL BONDS; DEUTERIUM; ISOTOPE EFFECTS; ISOTOPIC EXCHANGE; MASS SPECTROSCOPY; PROPANE
OSTI ID:
20650664
Research Organizations:
Commissariat a l'Energie Atomique, Saclay (France). Centre d'Etudes Nucleaires
Country of Origin:
France
Language:
French
Other Identifying Numbers:
TRN: FR05R3134090277
Availability:
Available from INIS in electronic form
Submitting Site:
FRN
Size:
60 pages
Announcement Date:
Nov 23, 2005

Citation Formats

Leicknam, J P. Isotope effects in mass-spectrometry; Les effets isotopiques en spectrometrie de masse. France: N. p., 1967. Web.
Leicknam, J P. Isotope effects in mass-spectrometry; Les effets isotopiques en spectrometrie de masse. France.
Leicknam, J P. 1967. "Isotope effects in mass-spectrometry; Les effets isotopiques en spectrometrie de masse." France.
@misc{etde_20650664,
title = {Isotope effects in mass-spectrometry; Les effets isotopiques en spectrometrie de masse}
author = {Leicknam, J P}
abstractNote = {In the first part, a review is made of the work concerning the influence of isotopic substitution on the stabilities of ionised molecules and the bond-breaking probabilities; metastable transitions are also affected by this substitution. A model based on the Franck-Condon principle accounts for the experimentally observed isotopic effects for diatomic molecules; to a certain extent it is possible to generalise the calculation for the case of isotopic molecules of carbon dioxide gas. For deuterated polyatomic molecules there exist a {pi} effect making it possible to compare the relative stabilities of the X-H and X-D bonds, and a {gamma} effect which characterizes the different behaviours of the X-H bond in a normal molecule and in its partially deuterated homologue. Usually there is a very marked {pi} effect (e.g. the C-D bonds are more difficult to break than the homologous C-H bonds) and a {gamma} effect, the partial deuteration of a molecule leading in general to an increase in the probability of breakage of a given bond. An interpretation of {pi} and {gamma} effects based on Rosenstock near-equilibrium theory accounts for the observed phenomena, qualitatively at least, in the case of propane and acetylene. In the second part are gathered together results concerning isotopic effects produced during the formation of rearranged ions. The existence of cyclic transition ions has made it possible for Mc Lafferty to explain the existence of these ions in the mass spectrum; isotopic substitution leads to a modification of the rearrangement mechanism, the bonding forces being no longer the same. (author) [French] Dans une premiere partie, on rassemble les travaux concernant l'influence de la substitution isotopique sur les stabilites des molecules ionisees et les probabilites de rupture des liaisons; les transitions metastables sont egalement modifiees par cette substitution. Un modele base sur le principe de Franck-Condon rend compte des effets isotopiques experimentalement observes avec les molecules diatomiques; dans une certaine mesure on peut generaliser le calcul au cas des molecules isotopiques de gaz carbonique. Pour les molecules polyatomiques deuteriees on distingue un effet {pi}, qui permet de comparer les stabilites relatives de liaisons X-H et X-D et un effet {gamma} qui caracterise le comportement different des liaisons X-H dans une molecule ordinaire et son homologue partiellement deuteriee. Le plus souvent on a un effet {pi} nettement marque (par exemple les liaisons C-D sont plus difficiles a rompre que les liaisons C-H homologues) et un effet {gamma}, la deuteriation partielle d'une molecule augmentant en general la probabilite de rupture d'une liaison C-H donnee. Une interpretation des effets {pi} et {gamma} basee sur la theorie du quasiequilibre de Rosenstock rend compte, au moins qualitativement, des phenomenes observes avec le propane et l'acetylene. Dans une seconde partie, on a regroupe les travaux concernant les effets isotopiques qui se produisent lors de la formation d'ions rearranges. L'existence d'ions transitoires cycliques a permis a Mc Lafferty d'expliquer l'apparition de ces ions dans le spectre de masse; la substitution isotopique modifie les mecanismes de rearrangement, les forces de liaison n'etant plus les memes. (auteur)}
place = {France}
year = {1967}
month = {May}
}