Substituent effect and target gas pressure dependence study of 4-RC6H4Ph (R = H, NO2, F, NH2, OH, Br, Ph) showed that the decomposition of double charged ion formed in the ion source is dominated by the loss of H, C2H2, C2H4, and HR (R = substituent). [C12H8]2+, [C12H6]2+, and [C10H6]2+, among others, are the most stable product ions. The various substituent effects in different decomposition reactions cannot be predicted by Hammett equation. While the total ion current of the 2E spectra was markedly influenced by the target gas pressure, the fragmentation pattern was independent of it.

Key words: INFLUENCE, MASS SPECTROGRAPHY, SUBSTITUENT EFFECT, DIPHENYL P, DISSOCIATION, DOUBLE-CHARGE ION