Electron transfer to oriented molecules:: Surprising steric effect in t-butyl bromide

Collisions between neutral K atoms and oriented t-butyl bromide molecules produce the ions K+ and Br- at energies high enough to separate charged particles (greater than or similar to4 eV). Ions are detected by coincidence tof mass spectrometry for orientation of the t-butyl bromide such that the K atom attacks either the Br end or the t-butyl end of the molecule. At high energies the steric asymmetry factor is larger than that for CH3Br. But at energies near threshold, the steric asymmetry factor reverses sign and attack at the t-butyl end becomes more reactive than attack at the Br end. The electron is apparently transferred into different orbitals at different ends. (C) 2001 American Institute of Physics.