The possible isomers of carbon trioxide include ones with molecular symmetry point groups Cs, D3h, and C2v.

Carbon trioxide can be produced, for example, in the drift zone of a negative corona discharge by reactions between carbon dioxide (CO2) and the atomic oxygen (O) created from molecular oxygen by free electrons in the plasma.

[2] Another reported method is photolysis of ozone O3 dissolved in liquid CO2, or in CO2/SF6 mixtures at −45 °C, irradiated with light of 253.7 nm.

The formation of CO3 is inferred but it appears to decay spontaneously by the route with a lifetime much shorter than 1 minute.

[3] Carbon trioxide can be made by blowing ozone at dry ice (solid CO2), and it has also been detected in reactions between carbon monoxide (CO) and molecular oxygen (O2).