Description:
<jats:p>
Although 248-nanometer radiation falls 0.12 electron volt short of the energy needed to dissociate O
<jats:sub>2</jats:sub>
, large densities of ozone (O
<jats:sub>3</jats:sub>
) can be produced from unfocused 248-nanometer KrF excimer laser irradiation of pure O
<jats:sub>2</jats:sub>
. The process is initiated in some undefined manner, possibly through weak two-photon O
<jats:sub>2</jats:sub>
dissociation, which results in a small amount of O
<jats:sub>3</jats:sub>
being generated. As soon as any O
<jats:sub>3</jats:sub>
is present, it strongly absorbs the 248-nanometer radiation and dissociates to vibrationally excited ground state O
<jats:sub>2</jats:sub>
(among other products), with a quantum yield of 0.1 to 0.15. During the laser pulse, a portion of these molecules absorb a photon and dissociate, which results in the production of three oxygen atoms for one O
<jats:sub>3</jats:sub>
molecule destroyed. Recombination then converts these atoms to O
<jats:sub>3</jats:sub>
, and thus O
<jats:sub>3</jats:sub>
production in the system is autocatalytic. A deficiency exists in current models of O
<jats:sub>3</jats:sub>
photochemistry in the upper stratosphere and mesosphere, in that more O
<jats:sub>3</jats:sub>
is found than can be explained. A detailed analysis of the system as it applies to the upper atmosphere is not yet possible, but with reasonable assumptions about O
<jats:sub>2</jats:sub>
vibrational distributions resulting from O
<jats:sub>3</jats:sub>
photodissociation and about relaxation rates of vibrationally excited O
<jats:sub>2</jats:sub>
, a case can be made for the importance of including this mechanism in the models.
</jats:p>