Formation of long-lived benzene ions during charge exchange ionization of 1,5-hexadiyne in an ion cyclotron resonance spectrometer

Guchte, W.J. van de; Hart, W.J. van der; Koning, Leo J. de; Nibbering, Nico M. M.; Dunbar, Robert C.

doi:10.1016/0168-1176(93)87049-x

Cited by 14 publications

(5 citation statements)

References 24 publications

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“…There are a large number of possible C 6 H 6 + isomers with at least 10 isomeric structures accessible below the lowest-energy dissociation limit for the benzene cation. − A possible rearrangement of the benzene cation generated by EI involves ring contraction to form fulvene (5-methylene-1,2-cyclopentadiene), which has the second lowest heat of formation next to the benzene cation. , The isomerization of the benzene ion to the fulvene structure is slightly endothermic (51 kJ/mol, 12.2 kcal/mol). − The results shown in Figure could be explained by the generation of the fulvene cation as the X + isomer during the EI ionization of benzene in the ion source. In this case, the C 6 H 6 + ions injected into the drift cell consist of a mixture of benzene and fulvene cations.…”

Section: Resultsmentioning

confidence: 97%

Mass-Selected Ion Mobility Studies of the Isomerization of the Benzene Radical Cation and Binding Energy of the Benzene Dimer Cation. Separation of Isomeric Ions by Dimer Formation

et al. 2003

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A mass-selected, ion mobility drift-cell technique has been used to study the isomerization of the benzene radical cation generated by electron impact (EI) ionization. Evidence is presented for the generation of both the benzene and fulvene cations, with a lower limit for the barrier of isomerization E a(benzene+• → fulvene+•) estimated as E a > 1.6 eV. The reduced mobilities of the benzene and fulvene cations are nearly similar, making it difficult to separate the two ions in pure helium. However, because of the large difference in the bonding of the benzene and fulvene cations with neutral benzene, the two isomeric ions are readily separated in the presence of neutral benzene in the drift cell. This suggests that isomer ions with similar mobilities can be separated on the basis of the degree of their associations with their neutral precursor in the drift cell. This separation concept allows us to discover the “hidden isomerization” process responsible for the generation of the fulvene cations via EI ionization of benzene. This also allows us to measure the equilibrium constant for the formation of the benzene dimer cation without interference from the fulvene isomer. The resulting binding energies (17.6 and 17.4 kcal/mol for (C6H6)2 +• and (C6D6)2 +, respectively) are smaller than that reported by Hiraoka and co-workers (J. Chem. Phys. 1991, 95, 8413) and similar to that measured by Meot-Ner et al. (J. Am. Chem. Soc. 1978, 100, 5466), both using pulsed high-pressure mass spectrometry. The binding energies of the proton-bound dimers in pyridine and triethylamine systems have been measured as 25.2 ± 1 and 20.9 ± 1 kcal/mol, respectively, and the binding energies of the protonated methanol clusters H+(CH3OH) n with n = 3−5 have been measured as 21.0, 14.3, and 11.3 kcal/mol, respectively, in good agreement with literature values. The combination of thermochemical properties with isomer identification provides valuable information on the structure−property relationship of molecular cluster ions. The novel concept of the separation of isomeric ions by dimer formation is expected to be of general application and may help to resolve important outstanding issues in the separation, structure, and chemistry of hydrocarbon radical cations.

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Section: Resultsmentioning

confidence: 97%

Mass-Selected Ion Mobility Studies of the Isomerization of the Benzene Radical Cation and Binding Energy of the Benzene Dimer Cation. Separation of Isomeric Ions by Dimer Formation

et al. 2003

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“…Given the height of the barrier relative to the isomers of protonated toluene and the low barriers between the latter, a significant kinetic shift is therefore to be expected in the time scale of the experiments. Moreover, particularly for ions derived from arenes, radiative stabilization may be significant and thereby compete with ion fragmentation. With respect to IRMPD experiments, photon emission would effectively reduce the heating rate of the ion in the laser pulse.…”

Section: Resultsmentioning

confidence: 99%

Dissociation Routes of Protonated Toluene Probed by Infrared Spectroscopy in the Gas Phase

et al. 2006

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The structures of C(7)H(9)(+) ions generated by protonation of toluene are investigated by means of gas-phase infrared spectroscopy in conjunction with labeling experiments and complementary mass spectrometric studies. In full consistency with previous studies, the unimolecular as well as the multiphoton-induced dissociation of mass-selected C(7)H(9)(+) ions lead to losses of molecular hydrogen and methane. Labeling data clearly imply the occurrence of skeletal rearrangements of protonated toluene to isomeric structures in the course of fragmentation. Complementary reactivity studies indicate, however, that the C(7)H(7)(+) ions generated upon dehydrogenation of C(7)H(9)(+) bear the benzylium structure, rather than that of the more stable tropylium ion. Combination of labeling data and extensive theoretical studies lead to a scheme for the fragmentation of protonated toluene, which can account for all experimental findings reasonably well. As far as infrared spectroscopy of gaseous ions is concerned, the present results confirm the structural predictions derived from theory and provide evidence for the existence of protonated cycloheptatriene but also pose some questions about the comparability of intensities in multiphoton dissociation and linear absorption spectra.

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“…•+ ions, having the benzene structure, which survive for at least a few hundred milliseconds. 83 Stabilization of the excited C 6 H 6…”

Section: 82mentioning

confidence: 99%

Kinetic Shifts

Lifshitz

2002

Eur J Mass Spectrom (Chichester)

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The kinetic shift is the excess energy required to observe detectable dissociation within a certain experimental time frame. Kinetic shifts are of central importance when energetic attributes are deduced from appearance energy measurements. Their importance has become of renewed interest since larger molecules are being studied mass spectrometrically. This is a review paper on the topic of kinetic shifts. It is made up of the following sections: Introduction, Definitions, Experimental methods, Statistical theories, Examples: Aromatic and polycyclic aromatic hydrocarbons, fullerenes, metal cation–water, –alcohol and –ether complexes, Conclusions.

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Formation of long-lived benzene ions during charge exchange ionization of 1,5-hexadiyne in an ion cyclotron resonance spectrometer

Cited by 14 publications

References 24 publications

Mass-Selected Ion Mobility Studies of the Isomerization of the Benzene Radical Cation and Binding Energy of the Benzene Dimer Cation. Separation of Isomeric Ions by Dimer Formation

Mass-Selected Ion Mobility Studies of the Isomerization of the Benzene Radical Cation and Binding Energy of the Benzene Dimer Cation. Separation of Isomeric Ions by Dimer Formation

Dissociation Routes of Protonated Toluene Probed by Infrared Spectroscopy in the Gas Phase

Kinetic Shifts

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