By applying to electrolysis cathodes a technique that produces essentially only oxides that are volatile at room temperature, spectroscopically determined masses between 222 and 351 atomic mass unit (AMU) are found that cannot be ascribed to known compounds. In particular the masses found between 231 and 240 AMU cannot be ascribed to random signals but do correspond to CO2, the carbon of which is a neutron-rich nuclide as predicted by a recent theory of polyneutron nuclear reactions.