A large-scale plasma was created in CO-N-2-H2O gas mixtures by high-power laser-induced dielectric breakdown. The composition of the mixtures used corresponded to a cometary and/or meteoritic impact into the Earth's early atmosphere. A multiple-centimeter-sized. reball was created by focusing near-infrared laser pulse into the centre of cell. The laser-plasma formation in the mixtures mainly leads to a production of CO2. The competition of the CO + CO -> CO2 + C and CO + OH -> CO2 + H reactions in the CO2 production was investigated using O-18 labeled water. An analysis of the isotopomers was carried out by means of high-resolution FTIR spectroscopy. (C) 2009 Elsevier B. V. All rights reserved.