Time-dependence of the isotope effects in the unimolecular dissociation of tertiary amine molecular ions

Autor:	Steen Ingemann, Steen Hammerum, Nico M. M. Nibbering, Peter J. Derrick, Els Kluft, Colin E. Allison
Rok vydání:	1991
Předmět:	Tertiary amine Chemistry Analytical chemistry Statistical weight Biochemistry Transition state Dissociation (chemistry) Ion Field desorption Intramolecular force Kinetic isotope effect Molecular Medicine Physics::Atomic Physics Nuclear Experiment Instrumentation Spectroscopy
Zdroj:	Organic Mass Spectrometry. 26:875-881
ISSN:	1096-9888 0030-493X
DOI:	10.1002/oms.1210261013
Popis:	The intramolecular secondary isotope effects on the α-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 δ-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.
Databáze:	OpenAIRE
Externí odkaz:	https://explore.openaire.eu/search/publication?articleId=doi_________::93a622d202aa2896335fc72836af33f6 https://doi.org/10.1002/oms.1210261013 Zobrazit plný text záznamu Plný text