A STUDY OF THE CHEMIIONIZATION REACTIONS OF CA, SR AND BA WITH O-2(X (3)SIGMA(G-))

Chemielectron and chemiion spectra resulting from the reactions of eff usive beams of Ca, Sr and BB (in their ground S-1 states) with ground state molecular oxygen O-2(X(3) Sigma(g)(-)) have been recorded using electron spectroscopy and mass spectrometry. The chemielectron spectra are similar for all three reactions exhibiting a strong near-zero ene rgy band and another band at higher electron energies. The chemiion sp ectra show O-2(+) M(+) and M(2)O(2)(+) as the major ions. The total io n current as well as the individual ion intensities, have been recorde d as a function of the extraction potential on the reaction cell. The results obtained indicate that the metal oxide dimer ion is the primar y chemiion, formed via an associative ionization reaction of a metal a tom with a long-lived metal superoxide intermediate MO(2). A two stat e potential energy curve model is proposed for the M(+) MO(2) reactio n to explain the shape of the experimental electron distribution.