PhotolysisWhat happens when light is absorbed by a molecule?
Let's look at the absorption of a photon of light by a hydrogen
molecule. If the photon of light contains just enough energy to
promote an electron from the lower energy level to the upper
one, the bond order decreases from 1 to 0. The bond is broken
and two hydrogen atoms are formed. If the photon is more
energetic, the hydrogen atoms will have excess kinetic energy.
Light breaks chemical bonds when the energy of the photon is
greater than the bond dissociation energy. What is the
wavelength required to break the H-H bond? What about molecular
oxygen? The O=O bond is stronger than the H-H bond. By the same
analysis, it would require light of 240 nm to break it. However,
this doesn't ususally happen in the troposphere. The 240 nm
light is very energetic. Very little of light in this frequency
range reaches the troposphere because most of it is absorbed in
the stratosphere. What frequency of light would be needed to
cleave the N2 molecule? The bond d