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

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 degrees 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. (Int J Mass Spectrom 179/180 (1998) 117-127) (C) 1998 Elsevier Science B.V.