The Reactivity of Electronically Excited Species

A general review of electronically excited species is centred on a discussion of the collisional behaviour of specific states arising from the overall ground state configurations for the atoms: magnified image Experimental rate data for the excited atomic species are surveyed with an emphasis on direct monitoring of the optically metastable states, principally by time‐resolved attenuation of atomic resonance radiation following pulsed initiation. The overall structure employed in the discussion is to consider the symmetry of the potential surfaces involved in the collision, mainly for encounters of the type A + BC and also A + BCD, using C s symmetry for the collision complex in both cases. Light atom‐molecule collisions are described in terms of the weak spin orbit coupling approximation and heavy atom‐molecule collisions, using ( J, Ω ) coupling via the method of extended groups. The ( J, Ω ) coupling procedure permits discussion of individual spin orbit atomic states and the collisional quenching data for these are considered in some detail, including isotope effects and theories of long range interaction which are concerned with near resonance E r̊ V transfer processes. Product states are also generally considered, especially for heavy atom‐molecule collisions that might lead to population inversions for electronically excited molecular diatomic molecules of interest to laser systems operating in the visible region of the spectrum. Some brief consideration of the atmospheric chemistry of species such as O(2 1 D 2 ), N(2 2 D 1 ) and N(2 2 P 1 ), atomic transition lasers for Br(4 2 P 1/2 ) and I(5 2 P 1/2 ), and stratospheric pollution by fluorinated hydrocarbons is also given.