VIBRATIONAL-SPECTRA OF MOLECULAR-IONS ISOLATED IN SOLID NEON .6. CO4-

When a Ne:CO2:O2 = 200:1:1 mixture is codeposited at approximately 5 K with a beam of neon atoms that have been excited in a microwave discharge, several prominent infrared absorptions appear in the resulting deposit. In addition to the absorptions of unreacted CO2, absorptions previously assigned to O4+ and O4- are present, and new absorptions appear at 697, 1256, 1865, and 1895 cm-1. Detailed isotopic substitution experiments demonstrate that these new absorptions are contributed by a product of formula CO4 in which the CO2 moiety is joined to O2 in such a way that the two O atoms of each of these groups are nonequivalent. Arguments are presented indicating that this product is the CO4- anion. The infrared frequencies of the isotopically substituted species have been used for a least-squares force constant adjustment calculation, assuming a planar O2C..O2-(C(s)) structure in which most of the negative charge remains on the O2 moiety. The photodestruction threshold of CO4- lies near 260 nm. Evidence has been obtained for the formation of CO3- or of CO3 in an excited state with 3-fold symmetry, for which randomization of the oxygen isotopic substitution occurs.