Lev Krasnoperov and Victor Stepanov
A new physical chemistry laboratory experiment has been developed in order to familiarize students with one of the modern experimental techniques of studying fast chemical reactions. The experiment is based on the laser pulsed photolysis coupled to transient UV spectroscopy. In addition, the experiment demonstrates the reaction of ozone formation in the upper atmosphere.
The reaction under study is the formation of ozone from oxygen atoms and oxygen molecules: O + O2 --> O3. Mixtures of molecular oxygen and nitrogen (5, 10, and 21%) are pumped through the flows cell at ambient temperature and pressure. The mixtures are irradiated by light from an ArF pulsed excimer laser (193 nm), which leads to photodissociation of a small fraction of oxygen molecules yielding oxygen atoms. Oxygen atoms rapidly react with oxygen molecules producing ozone. The ozone concentration build-up in the reactor is monitored via its transient absorption at 253.7 nm (resonance line of Hg). The reaction rate constant typically obtained by the students is (5.0 + 1.2) x 10-34 cm6molecule-2sec-1, in good agreement with the literature data.
SUMMARY AND DISCUSSION