Collision induced dissociation of the isometric ions H 2COOH + and HC(OH) +12

Abstract

The dissociation of two isomeric forms of the ion CH 3O + 2 induced by collisions with the helium buffer gas atoms has been studied in a selected ion flow drift tube (SIFDT) experiment. When CH 2OOH + is formed via the reaction of O 2 + with CH 4, the product ions from collision induced dissociation (CID) are HCO + (60%) and H 3O + (40%) respectively, independent of the mean relative collision energy E c between the buffer gas and the ions, from thermal to 0.2 eV. The Arrhenius activation energy obtained is 24 kcal mol −1. Protonation of formic acid leads to HC(OH) + 2 ions, the CID of which yields 50% HCO + and 50% H 3O +, also independent of E c. The Arrhenius activation energy is 38.4 kcal mol −1. When formic acid is protonated in reaction with D 3O + to form CH 2DO + 2, the products of CID of this ion are HCO + and DH 2O + only, showing that deuteration occurs on the oxygen alone and not on the carbon HC(OH) + 2 performs fast isotope exchange in collisions with D 2O to form HC(OD) + 2 in two consecutive steps and, again, deuteration on the carbon atom is not observed HC(OH) + 2 also rapidly collisionally associates with H 2O( k≈10 −27 cm 6 s −1 at 300 K).