Charge-Exchange Phenomena in a Mass Spectrometer

The previous study of the ionization probabilities has been extended to include additional high molecular weight unsubstituted polynuclear aromatic hydrocarbons. The charge distributions for these ions were calculated using Hückel molecular orbitals. These charge distributions were used to calculate a geometric charge cross section by an impact parameter approach assuming a simple classical collision model. The geometric charge cross sections were found to correlate with the molecular ionization probabilities for the unsubstituted compounds, suggesting that the relative ionization probabilities for these compounds result from purely geometric considerations. The polymethylbenzene series was studied to determine whether the marked effect of substituent groups is purely geometric or whether additional group effects exist. It was found that a 3.3-fold greater group efficiency of methyl groups relative to the ring carbon atoms was necessary to correlate with these data. A number of nitrogen heterocyclics were also studied. The single-ring heterocyclic series showed a significant reduction of the ionization probability with nitrogen substitution. These results did not agree with the HMO calculations suggesting that ionization of the π-electron system does not play a dominant role in the threshold ionization probability for these compounds. By contrast, the quinolines and phenazine gave agreement with the geometric charge cross section due to their lower π-ionization energies.

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Charge-Exchange Phenomena in a Mass Spectrometer

Cited by 4 publications

References 1 publication

Ion‐Neutral Reactions

Ion‐Neutral Reactions

Organic Ions in the Gas Phase. XV. Decomposition of n-Alkanes under Electron Impact

Correlation of Ionization Probabilities with Geometric Charge Cross Sections

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