UNSPECIFIED. (1991) TIME-DEPENDENCE OF THE ISOTOPE EFFECTS IN THE UNIMOLECULAR DISSOCIATION OF TERTIARY AMINE MOLECULAR-IONS. ORGANIC MASS SPECTROMETRY, 26 (10). pp. 875-881. ISSN 0030-493X

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Abstract

The intramolecular secondary isotope effects on the alpha-cleavage of deuterium-labelled N-methyldipentylamine radical cations have been studied as a function of ion lifetime by field ionization kinetics. The isotope effects observed are all normal and increase in magnitude with increasing ion lifetime, with the exception of the delta-labelled compound which shows an inverse effect (predominant loss of the labelled radical) at times shorter than 10(-9)s, and a normal effect at longer times. The isotope effects reflect differences in zero-point energies of the transition states as well as the influence of slight reductions of isotope-dependent frequencies on the state sums-a statistical weight effect. The latter is particularly important at high ion energies and is the primary reason for the occurrence of the inverse isotope effect. The time dependence of the normal and inverse isotope effect is reproduced by QET/RRKM calculations.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry Q Science > QC Physics
Journal or Publication Title:	ORGANIC MASS SPECTROMETRY
Publisher:	JOHN WILEY & SONS LTD
ISSN:	0030-493X
Date:	October 1991
Volume:	26
Number:	10
Number of Pages:	7
Page Range:	pp. 875-881
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/22454

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