Journal of Chemical Physics, Vol.110, No.19, 9426-9434, 1999
State-selected ion-molecule reactions: The charge-transfer N-2(+)(X,v(+))+O-2 -> O-2(+)+N-2
The charge-transfer process, which is the subject of this paper, is an important link in the chain of reactive events which occur in the E- and F-regions of the earth's atmosphere. The reaction is suspected to proceed via the formation of a short-lived intermediate complex (N-2. O-2)(+). The transient existence of this van der Waals molecule has been inferred from molecular orbital and ab initio arguments. To the present day, however, none of the numerous studies focusing on this system has provided proof of its existence. The positive evidence obtained from this experiment is of an indirect nature, based on measurements of the kinetic energy of the released O-2(+) as a function of the expendable center-of-mass collision energy. The results point to an indirect reaction (i.e., via an intermediate) in the low energy regime, and a direct process once the center-of-mass energy exceeds the bond energy of the complex. A model description which contracts both pictures matches the complete set of energy-dependent cross section data in a very persuasive manner. A competing reactive channel which has also been given attention results in the formation of NO+. The initiation of this reaction requires a cleavage of the N-N bond, which should be eased by vibrational excitation of the reagent ion. The cross section data, however, turn out to be unaffected by such details of reagent state preparation.