Chemical ionization of the nitrate ester explosives EGDN and PETN by trimethylsilyl cation and comparison of the reactivity of nitrate ester and nitro explosives toward trimethylsilyl cation

Abstract

Fourier transform ion cyclotron resonance mass spectrometry has been used to examine the reactions of Si(CH_3)_3)^+ with EGDN and PETN. In addition, the reactions of Si(CH_3)_3^+ with EGDN and PETN was examined in a magnetic sector mass spectrometer. No adduct formation was observed with either EGDN or PETN in the Fourier transform ion cyclotron resonance mass spectrometer, but characteristic fragment ions are seen. Both EGDN and PETN form adducts with Si(CH_3)_3^+ in the sector mass spectrometer. The bimolecular rate constant for the reaction of Si(CH_3)_3^+ with EGDN is measured to be 0.91 × 10^(−10) cm^3 s^(−1) molecule^(−1), and the bimolecular rate constant for the reaction of Si(CH_3)_3^+ with PETN is estimated to be 8 × 10^(−10) cm^3 s^(−1) molecule^−1). Collision-induced dissociation experiments were performed on the major fragment ion products to characterize the observed fragmentation patterns. The fragment ions observed in both cases are characteristic of each explosive and could be useful in the analytical detection and identification of EGDN and especially PETN. Reaction coordinate diagrams for the reactions of EGDN and PETN with Si(CH3)3+ are derived (from known thermochemistry and semi-empirical calculations on the involved species). The reactivity of nitro and nitrate ester explosives with Si(CH_3)_3^+ is compared and reasons for their different chemical behavior are discussed.