Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

288 DETECTION AND ESTIMATION OF INTERMEDIATESserved the chemiluminescent reaction between alkali metals and halogens. Theprocesses leading to excitation were suggested to beNa + Cl, -+NaCl+ C1C1+Naz + NaC1' +NaNaClt + Na -+ NaCl + Na*(for the sodium-chlorine reaction)NaC1' represents a molecule of vibrationally excited sodium chloride, while Na*is an electronically excited, 'P, sodium atom which emits the resonance radiation.It will be remembered that these studies made very significant contributions tofundamental theories of reaction kinetics, especially with regard to the understandingof the potential energy surface describing reactions, activated complexand products.Emission spectroscopy has been used recently in an elegant attempt to elucidatethe mechanism of the energy transfer process (10). Moulton and Herschbach"have examined the emission from a triple molecular beam experiment. Molecularbeams of bromine and atomic potassium cross each other, and vibrationally excitedKBr is formed, which is then collimated into a further beam.K+Br, + KBrt+BrThe beam of KBr now meets a beam of atomic sodium, and the radiation emittedturns out to be of thepotassium resonance lines, so that the energy transfer processmust be writtenKBrt+Na + K*+NaBrJohn Polanyi and his collaborator^^^-^^ have used the infrared emission fromvibrationally excited HC1 to give information about the potential energy surfacefor the reactionH+Cl, + HClt+C1 (13)The observations of the various vibrational bands may be used to determine theinitial energy distribution of the excited hydrogen chloride. This knowledge of theenergy distribution may then be used to test empirical contour maps for the reactionsurface.The participation in reaction of electronically excited oxygen molecules (in the'X: and 'A,, states) has of late drawn much interest, and emission spectroscopyhas played an important part in the identification and estimation of the singletmolecules. Hornbeck and Herman44 observed the emission from the 02('Zz-3ZC,-)