A determination of the effective temperatures for the dissociation of the proton bound dimer of dimethyl methylphosphonate in a planar differential mobility spectrometer

The dissociation of the proton bound dimer of dimethyl methylphosphonate to the protonated and neutral molecule has been studied in a planar differential mobility spectrometer. The internal energy of the ions is the sum of the thermal component and the electric field component and results in an effective temperature, T eff , that is significantly greater than that of the ambient atmosphere temperature, T. The measured rate constant for dissociation, which rises exponentially with field strength, together with activation energy and pre-exponential factor previously determined under thermal conditions, allow the calculation of T eff as a function of electric field strength. T eff is a linear function of electric field intensity at constant T over the range of T from 60 °C to 140 °C. The efficiency of the available collision energy in causing dissociation decreases with increasing T, from 52% at 60 °C to 40% at 140 °C.