Effect of buffer gas alterations on the thermal electron attachment and detachment reactions of azulene by pulsed high pressure mass spectrometry

A principal motivation for the present study is to determine the ion source conditions required for achievement of the high pressure limit (HPL) of kinetic behavior for the resonance electron capture (REC) reaction of azulene (Az), Az + e --> Az(-). This goal is accomplished here by measuring rate constants for the reverse process, thermal electron detachment by molecular anions of azulene, Az(-) --> Az + e, by pulsed high pressure mass spectrometry by using a variety of buffer gases, methane, argon, nitrogen, and helium, over a range of pressures, from 1 to 6 Torr, over a range of temperatures, from 150 to 200 degrees C. From these measurements, it is shown that the ion source conditions commonly used in electron capture mass spectrometry for the trace analysis of REC-active molecules would not be sufficient for achievement of the HPL of the REC reaction of azulene and, therefore, would likely result in significantly reduced sensitivity to this compound. The problem highlighted here for the case of azulene is undoubtedly shared by many other REC-active compounds. The resolution of this problem is expected to require accommodation of several relevant factors shown here to be important in the case of azulene, including the choice of buffer gas, pressure, and ion source temperature. (C) 2000 Elsevier Science B.V.