So, Chapman proposed that as soon as one of these oxygen atoms («free radicals») collided with
an ordinary diatomic oxygen molecule, they would react together to form a single triatomic ozone molecule (Figure 18).
The forces holding diiodine molecules in the crystal are modest, and liquid iodine is not stable at
ordinary temperatures and pressures, so that solid iodine sublimes to give a rather large concentration of
diatomic molecules in the vapor phase.