Excitation of alkali metal salts

The reactions of sodium and potassium atoms with halogens, nitrogen oxides 

The reactions are fast. Activation energies greater than 5kcal.mole-1 are unusual (and not well established). Observed chemiluminescence is often that of the alkali metal atom (D-line radiation), although for some cases (Na reactions with inorganic polyhalides), diffuse radiation from a molecular product has been observed. 

The mechanism that explains the chemiluminescence is, for the traditional example 

The sodium D-line radiation dominates the system because the Nad is long-lived, the vibrational-electronic energy transfer is efficient and the excited atom radiates in 10-B seconds. The multistep process bleeds off the excitation energy. This behavior probably is common in systems containing atoms with low-lying energetically accessible electronic states29,55. 

Crossed molecular beams have been used to study nearly as wide a range of alkali metal atom reactions as has been examined by diffusion flames. An excellent review has been provided by Herschbach2. The multi-step mechanism displayed for chemiluminescence studies does not apply to the scattering experiments. Only the initial bimolecular reaction is important at the low pressures used. 

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