Peak Contour and Half-Life of Metastable Ions Appearing in Mass Spectra

A method is described for determining the half-lives of metastable ions by varying the voltage which sweeps the ions from the ionization chamber of a mass spectrometer. The halflife of the state corresponding to the transition C₄H₁₀⁺→{C}₃H₇⁺+[CH₃] has been found to be 2.0×{}10^-6 second and the value found for the transition C₄H₁₀⁺→{C}₃H₆⁺+[CH₄] was 1.7×{}10^-6 second. In answer to the objection that the diffuse peaks should not be prominent in the 180^∘{} instrument if they are to be attributed to spontaneous dissociation during transit, it is shown that this result is to be expected for metastable transitions. The relative number of ions in the metastable states initially is estimated.