If I had a container in vacuum filled with $\ce{I2}$ gas and then I bombarded it with high speed electrons using an electron gun, would be able to get both $\ce{I+}$ and $\ce{I-}$ ions or would I only get $\ce{I2+}$ plus an ejected electron?

  • $\begingroup$ also, if I supply I2 with low energy electrons would the iodine attract the electron due to its high electron affinity? $\endgroup$
    – Arash M.
    May 12, 2015 at 9:37
  • $\begingroup$ Yes, it is likely that one of the iodine atoms in this case will indeed capture the bombarding electron. $\endgroup$
    – Wildcat
    May 12, 2015 at 10:01

1 Answer 1


Sure, why not. It's just the question of your bombarding electrons having the right energy. At low energies, a bombarding electron will likely be captured by one of the iodine atoms: $$ \ce{I2 + e- -> I- + I} \, . $$ But somewhere around $8.62 \pm 0.06 \, \mathrm{eV}$ according to this study, you'll indeed have the ion pair formation: $$ \ce{I2 + e- -> I- + I+ + e-} \, . $$ There are some other processes which contribute to the ion pair formation. For details, read the paper quoted above.

With respect to the formation of $\ce{I2+}$ note that to form it a bombarding electron have to, formally speaking,

  • Either first break the $\ce{I-I}$ bond homolyticly and then remove two electrons from one of the $\ce{I}$ atom which requires it to carry about 30 eV of energy (the sum of the homolytic bond dissociation energy and of the first and the second ionization energies).
  • Or break the $\ce{I-I}$ bond heteroliticly and then remove the second electron from $\ce{I-}$ ion which requires it to carry also about 30 eV of energy (the sum of the heterolytic bond dissociation energy and of the second ionization energy).



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