THRESHOLD ENERGIES FOR THE REACTIONS OH-+CH3X-]CH3OH+X-(X=CL,BR) MEASURED BY TANDEM MASS-SPECTROMETRY - DEPROTONATION ENERGIES (ACIDITIES) OF CH3CL AND CH3BR

In a tandem mass spectrometer, a beam of OH- ions was reacted with methyl chloride and methyl bromide at collision energies in the range 0.2 < E(T) < 5 eV. For both of the methyl halides, excitation functions, sigma(E(T)), were measured for the two competing channels, endoergic proton transfer and exoergic nucleophilic displacement: OH- + CH3X --> H2O + CH2X---> CH3OH + X-The threshold energies estimated for the proton transfer reactions are used to derive energies of deprotonation for CH3Cl and CH3Br of 1672 +/- 10 and 1660 +/- 10 kJ mol-1 respectively.