Premium
Mass Spectrometric Studies of Fullerene Ion Beams
Author(s) -
Laskin Julia,
Lifshitz Chava
Publication year - 1997
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199700052
Subject(s) - chemistry , reflectron , metastability , kinetic energy , ion , fullerene , mass spectrometry , atomic physics , analytical chemistry (journal) , radiative transfer , time of flight mass spectrometry , ionization , physics , optics , chromatography , organic chemistry , quantum mechanics
The energetics and dynamics of C 2 evaporations from carbon cluster ions C n + were studied using time‐resolved mass spectrometric techniques. Time‐resolved appearance energies (AEs) were determined for C 58 + and C 56 + on a double‐focusing mass spectrometer using electron‐space‐charge trapping. The AEs were found to be nearly independent of time for times longer than 80 μs. A large intrinsic kinetic shift, IS=30.5 eV, was observed. This intrinsic shift is due to radiative decay in the visible, which is unusually efficient for fullerenes. Time‐resolved kinetic energy releases (KERs) and metastable fractions (MFs) for C n + (n = 48 −62) were measured on an ion trap/reflectron mass spectrometer for trapping times up to 100 μs. The average KER for C 2 evaporation from fullerenes was observed to decrease with increasing precursor ion lifetime. This constitutes proof that the KER is due to the non‐fixed energy in the transition state rather than to a reverse activation energy, and the reaction takes place via a loose transition state. The metastable fractions decrease with increasing trapping time, as expected. The results obtained for C 58 + → C 56 + + C 2 are successfully modeled taking into account radiative cooling. The shape of the plot of MFs versus ln(t 2 /t 1 ) (where t 1 and t 2 are the times corresponding to the beginning and the end of a metastable time window, respectively) is mainly defined by the relation between dissociative and radiative rate constants.