Thermal electron detachment of the molecular anion of azulene at elevated pressures by ion mobility spectrometry

Abstract

Rate constants, k TED, and their temperature and pressure dependence for the thermal electron detachment (TED) reaction of the molecular anion of azulene (Az − → Az + e) have been determined by ion mobility spectrometry (IMS). By this method, Az − ions are periodically introduced to a drift tube containing nitrogen gas at pressures ranging from 300 to 1100 Torr and temperatures ranging from 75 to 175 °C. During the time required for an Az − ion packet to drift to a Faraday detection plate, either a portion (at lower temperatures) or essentially all (at higher temperatures) of the Az − ions undergo TED. From the TED-modified IMS waveforms thereby produced, the magnitudes of k TED values have been deduced and compared with previous measurements of k TED for Az − made in buffer gases of much lower and higher pressures. The present results support a trend noted in the prior studies that the rate of TED by Az − is decreased by large increases in pressure to the near-atmospheric pressure range. A potential explanation of this unexpected effect of a buffer gas that is normally considered to be chemically inert is that a weak chemical interaction exists between the Az − ion and the nitrogen buffer gas molecules and this provides increased stability to the Az − ion under conditions of very high pressure and thereby increases the activation barrier of the TED reaction.