Spectroscopic Study of the Br^- +CH₃ I→I^- +CH₃ Br S_N 2 Reaction.

Mass spectrometry and anion photoelectron spectroscopy have been used to study the gas-phase S N 2 ${{{\rm S}}_{{\rm N}}2}$ reaction involving B r - ${{{\rm B}{\rm r}}^{-}}$ and C H 3 I ${{{\rm C}{\rm H}}_{3}{\rm I}}$ . The anion photoelectron spectra associated with the reaction intermediates of this S N 2 ${{{\rm S}}_{{\rm N}}2}$ reaction are presented. High-level CCSD(T) calculations have been utilised to investigate the reaction intermediates that may form as a result of the S N 2 ${{{\rm S}}_{{\rm N}}2}$ reaction along various different reaction pathways, including back-side attack and front-side attack. In addition, simulated vertical detachment energies of each reaction intermediate have been calculated to rationalise the photoelectron spectra.