The ion kinetic energy and mass spectra of isomeric methyl indoles

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Abstract
The mass spectra of the seven isomeric methylindoles were recorded and the [metastable ion]/[daughter ion] ratios for the reactions m/e 130 → m/e 103 and m/e 103 → m/e 77 have been obtained. The ratios indicate that the decomposing [M — 1] ions (m/e 130) from the 4, 5, 6 and 7 isomers are energetically similar as are the [M — 1] ions from the 2 and 3 isomers. The results observed for the m/e → 103 m/e 77 reaction showed that the decomposing m/e 103 ions from the 2, 3, 4, 5, 6 and 7 isomers all have the same energy distribution. N‐Methylindole gave ratios which were similar to the 4 to 7 isomers at 70eV but different at 20 eV. The ion kinetic energy (IKE) spectra of all the isomeric methylindoles were also obtained and the results compared with the data obtained from the [metastable ion]/[daughter ion] approach. The results from the IKE spectra indicated that the energy distributions of the [M — 1] and [(M — 1) — HCN] ions from 1‐methylindole and the [(M — 1) — HCN] ions from 2‐methylindole could readily be distinguished from other isomers whose [metastable ion]/[daughter ion] ratios were similar. Thus by using both techniques certain ambiguities can be resolved.