Electron impact ionization cross-sections of n-heptane

Electron impact ionization of n-heptane was studied using mass spectrometry. Cross-sections for the formation of molecular ion and ionic fragments are measured between 10 eV and 86 eV with a total cross-section of 1.5 × 10−16 cm2 towards 50 eV. The molecular ion is the most abundant below 16 eV. The present results display good agreement between the measured total ionization cross-sections and the calculated one with the BEB model. Five ions CnH2n+1+ (2 ≤ n ≤ 6) result from a simple C–C bond split in the molecular ion. C3H7+, identified as isopropyl cation, is the most abundant of the ionic species above 16 eV. Four ions CnH2n+ (2 ≤ n ≤ 5) result from a C–C bond split with H-atom rearrangement. C3H6+, identified as propene cation, is the most abundant of these four cations above 35 eV. Five other ions, CnH2n−1+ (2 ≤ n ≤ 4), cyclopropenyl and methyl cations may result from the ionization of C4H9, the major alkyl issued from the fragmentation of the molecular ion.

Electron impact ionization cross-sections of the two major cations issued from n-heptane from 10 eV to 90 eV. Total ionization cross-section measured and calculated with the BEB theory.Figure optionsDownload high-quality image (94 K)Download as PowerPoint slide