Multiexponential decay of negative molecular ions as a result of target molecule distribution over vibrational states

The lifetimes of long-lived negative molecular ions SF₆⁻-, C₆H₅NO₂⁻, and C₆F₆⁻ are measured with a static mass spectrometer. A great spread in published data for the lifetimes of these ions is explained using a concept of multiexponential decay of molecular ions. The influence of the Boltzmann distribution of neutral target molecules over vibrational states on the lifetime of negative molecular ions is studied in terms of the Illenberger-Smirnov-Kompaneits simple statistical model. It is shown that this distribution has a profound effect on the multiexponential decay of molecular anions and, as a consequence, on the lifetime of negative molecular ions measured on different mass spectrometers.