CHEMICAL-IONIZATION OF TNT AND RDX WITH TRIMETHYLSILYL CATION

Fourier transform ion cyclotron resonance mass spectrometry has been u sed to examine the reactions of Si(CH3)(3)(+) with nitrobenzene, TNT, and RDX With nitrobenzene, the only reaction observed is adduct format ion which generates the C6H5NO2Si(CH3)(3)(+) ion. The bimolecular rate constant for the reaction of Si(CH3)(3)(+) with nitrobenzene is measu red to be 1.8 x 10(-9) cm(3) s(-1) molecule(-1). With TNT, fragmentati on and adduct formation were observed. The bimolecular rate constant f or the reaction of Si(CH3)(3)(+) with TNT is measured to be 0.85 x 10( -9) cm(3) s(-1) molecule(-1). With RDX, the dominant reaction observed is adduct formation, but some fragmentation is seen as a minor reacti on pathway. The bimolecular rate constant for the reaction of Si(CH3)( 3)(+) with RDX is estimated to be similar to that observed with TNT (s imilar to-0.7 x 10(-9) cm(3) s(-1) molecule(-1)). Collision-induced di ssociation experiments performed on both the TNT-Si(CH3)(3)(+) and the RDX-Si(CH3)(3)(+) adducts using off-resonance collisional activation show the same fragmentation pattern that is observed during adduct for mation. This fragmentation pattern appears to be a ''fingerprint'' for both adducts. These reactions appear to be driven by the high affinit y of Si for oxygen and the attraction of the Si(CH3)(3)(+) ion to the formal negative charge of oxygen in a nitro group. A reaction coordina te diagram for reactions of RDX with Si(CH3)(3)(+) is derived (from kn own thermochemistry and ab initio calculations on the reactive interme diates) and its implications are discussed. Reactions of this type cou ld be useful as a detection scheme for common explosives.