Doubly charged ion mass spectra: III—<i>N</i>‐alkanes

Abstract

Abstract Doubly charged ion mass spectra have been obtained for 15 n ‐alkane hydrocarbons. Spectra were measured using a Nier‐Johnson geometry Hitachi RMU‐7L mass spectrometer operated at 1.6kV accelerating voltage. Fragment ions, which resulted from CC bond rupture and extensive H loss, dominated the spectra. Molecular ions have not been observed. The most intense ions in the doubly charged ion mass spectra of n ‐alkanes were [C 2 H 4 ] 2+ , [C 3 H 2 ] 2+ , [C 4 H 3 ] 2+ , [C 5 H 2 ] 2+ , [C 6 H 6 ] 2+ , [C 6 H 8 ] 2+ , [C 7 H 6 ] 2+ , [C 7 H 8 ] 2+ , [C 8 H 6 ] 2+ and [C 8 H 8 ] 2+ . Appearance energies for forming the prominent doubly charged fragment ions have been measured and range from 27.5 eV to energies greater than 60eV. A geometry optimized SCF approach has been used to compute the energies and structures of prominent ions in the doubly charged mass spectra.