Scientists have discovered a new way to make molecular oxygen (O2) from carbon dioxide (CO2) -- no green plants involved.
Their findings could alter our understanding of the Earth’s early atmosphere and how oxygen might form on other planets with carbon dioxide in their atmospheres.
In a paper published Thursday in Science, researchers from UC Davis report that when carbon dioxide molecules are exposed to certain wavelengths of light radiation, they can get so excited that they split into a C molecule and an O2 molecule.
Previously it was thought that a carbon dioxide molecule would split into a CO and an O molecule no matter what wavelengths of light were involved, because that is the path of least resistance -- molecularly speaking.
The energy required to break a carbon dioxide molecule into a CO+O is a little more than five electron volts (EV), but to form C+O2 you need about 11.44 EV, the researchers said.
The results of the study were hypothesized by theoretical chemists a few years ago, but they had never measured until now.
“Understanding the behavior of even simple molecules like CO2 at high energies is very challenging,” said Arthur Suits, a chemist at Wayne State University in Detroit, who was not involved in the study. “Theory and experiment are still developing.”
In experiments in the lab, the researchers say the C+O2 result occurred just 5% of the time when carbon dioxide molecules encountered powerful light radiation in a vacuum.
“When you shine C02 with these high wavelengths of light, it can break apart along more than one channel,” said Cheuk-Yiu Ng, a professor of physical chemistry at UC Davis and an author of the paper. “These channels are energy dependent but at the energy we investigated, only 5% of these excited CO2 would go on to become C+O2.”
Suits said the findings have implications for how molecular oxygen (O2) may have formed in the Earth’s outer atmosphere, in other planetary atmospheres, and perhaps in the outflows of dying stars and interstellar molecular clouds.
Sean Crowe, a biogeochemist at the the University of British Columbia who was not involved with the study, said more research needs to be done to understand what role this newly discovered pathway for O2 production played in the atmosphere of the early Earth.
“We may have to revise our models for how much photochemical oxygen there was from this new paper,” he said. “Someone will have to look at that more closely in the future.”
Ng put it this way: “For 40 years people have been trying to understand how the planetary atmosphere transformed from what we see on Mars and Venus to what we see on Earth. They never included this process in their models, but our work shows it should be taken into account."