Reactions Involving Electronically-Excited Oxygen

Abstract

The vario~is electronically-excited states of oxygerl atoms and molec~~les are briefly considered. Certain reactio~ls involving sonle of these electronically-excited species are then disc~issed with reference to the experimental evidence and to the potential-energy surfaces on which they occur. In the case of the mercury-photosensitized formation of ozone fro111 osygen it is concluded that both experilnental evidence and theoretical arguments point to the fact that the oxygen molecule initially formed is in an excited 32,f state. Consideration is also given to the mechanism of formatioi~ of O?* in the carbon monoxide flame and in other flames. The reactions 0+03 -t 20,* and 0 2 * + 0 3 -t 2 0 ? + 0 are also disc~issed briefly. INTRODUCTIONA considerable number of electronically-excited states of oxygen molecules and atoms are known to exist, and spectroscopic data have provided detailed information about many of them. Several of these excited species are known to be involved ill chemical reactions, either as reactants or as products. The purpose of this paper is to refer to a few of the more common reactions of this type, to discuss the evidence for the nature of the species involved, and to consider detailed reaction mechanisms from the standpoint of the method of potential-energy surfaces.~ ELECTRONIC STATESThe electronic states of 0 and 0 2 will be mentioned only very briefly, since this matter has been fully discussed elsewhere (14,15). According to the Wigner-Witmer correlation rules two atoms of oxygen in their ground states (3P,) can produce, on combiilation, 18 different electronic species of the molecule, while one ground state atom plus one in the first excited level ('D,) can give an additional 18 species. Only a few of these are stable or relatively abundant, and Fig. 1 shows the potential-energy curves for those states of the molecule that have been observed spectroscopically. The IB; and 3Au states (3Au not drawn) have been detected by Herzberg (IG).The ground state of 0 2 (38;) and the first two excited states ('A, and '2;) have the electronic configuration and dissociate to normal 3P, atoms as shown in the figure. Additional excited states are formed by the transfer of an electron from the bonding (a,2p) orbital to the antibonding (~~2 9 ) orbital to giveThis configuration could produce the states 'Zi, ' 8;, 'A,, 32,+, 32;, and 3A,, of which ' 2;, 32,+, 32y, and 3A, have been observed. 3Z; dissociates into 0(3P,)+O(1D,), the rest into ground-state 0(3P,) atoms. For personal use only.

Singlet oxygen in the environmental sciences. Singlet molecular oxygen and photochemical air pollution

“…per mole for the 1Ag and "+ states, respectively. Calvert and Pitts (1966), Gill and Laidler (1958), Griffith (1964), and Wayne (1967Wayne ( , 1969 discuss electronically excited molecular oxygen in greater detail than is possible here.…”

A new source of ozone in the terrestrial upper atmosphere?

“…• [Dickinson and Sherrill, 1926;Noyes, 1927;Volman, 1954Volman, , 1956Volman et al, 1959;Gill and Laidler, 1958]. Reaction (2) also has been suggested as the source of ozone in gas discharges [Benson and Axworthy, 1959;Benson, 1959].…”

The Role of Excited Oxygen Molecules in the Formation of the Secondary Ozone Layer at 87 to 97 km

“…The Schumann-Runge bands have been observed in hydrogen, carbon monoxide and ammonia flames. This suggests that there may be a reaction common to all flames such as [52]:…”