Carbon Trioxide: Its Production, Infrared Spectrum, and Structure Studied in a Matrix of Solid CO2

Abstract

Reactions of oxygen atoms with CO2 molecules to give a species identified as CO3 have been observed in three systems: (1) the photolysis of solid CO2 at 77°K with vacuum-ultraviolet light from a xenon resonance lamp; (2) the photolysis of O3 in a CO2 matrix at 50°—60°K with 2537-Å light from a mercury arc; and (3) the radio-frequency discharge of CO2 gas followed by trapping of products at 50°—70°K. The infrared spectrum of the species includes absorptions at 568, 593, 972, 1073, 1880, 2045, 3105, and 3922 cm−1. Isotopic studies using CO2 enriched with 18O or 13C show that the molecular formula is CO3 and provide a basis for determining the molecular structure. Frequency assignments and isotopic product-rule calculations favor a planar C2v molecule in which the carbon atom is bonded to the unique oxygen atom by a strong carbonyl bond and to two equivalent oxygen atoms by weaker bonds. There is presumably covalent bonding between the two equivalent oxygen atoms. In the proposed frequency assignment it is assumed that the absorption arising from the out-of-plane bending mode is unobserved. Results of photolyzing isotopically nonequilibrated 18O-enriched CO2 indicate that a D3h or C3v species with three equivalent oxygen atoms is involved in the reaction mechanism or is a readily accessible excited state. There is evidence that the observed photodecomposition of CO3 by visible and ultraviolet light yields oxygen atoms and CO2.