What is the structure of carbon dioxide

Carbon dioxide as a climate pest is much discussed, carbon dioxide as a hard, transparent solid is new: Italian researchers transformed the gas into a kind of glass under high pressure. Previously, this had only been possible in computer simulations.

Florence (Italy) - The very hard, transparent material, so-called amorphous carbon dioxide (a-CO2), could also occur naturally inside large gas planets, according to the researchers. It promises interesting applications on earth if it is possible to maintain this solid state of the gas. So far, when the pressure is released, it has always turned back into its volatile form. In addition to technical fields of application, the new material could also be welcomed by environmentalists in order to effectively remove excess CO2 from the atmosphere.

"State-of-the-art spectral measurements have confirmed the amorphous structure of the material," reports the team led by Federico Gorelli and Mario Santoro from the European Laboratory for Non-Linear Spectroscopy (LENS) in the journal Nature, "Comparisons with data for amorphous silicon dioxide and amorphous silicon dioxide Germanium dioxide show that amorphous carbon dioxide has the same structure as the other dioxide glasses of the fourth main group of elements ". In the periodic table of the elements, carbon belongs to the same chemical group as silicon and germanium, which when combined with oxygen form glass-like structures. If the molecules in the silicon dioxide are arranged to form a crystal lattice, then quartz is found; if they are next to each other in a disordered, amorphous form, this is the main component of window glass. In contrast to the other members of this chemical group, carbon does not form solid materials in combination with oxygen at normal pressure and temperature. Only when carbon dioxide is cooled down and pressurized does so-called dry ice form with a lattice structure, which slowly evaporates again at normal pressure. Up until now, amorphous structures could only be created using a computer model.

The Italian team exposed its carbon dioxide in a pressure chamber at room temperature to pressures of up to 48 gigapascals - 480,000 times atmospheric pressure. Measurements with X-ray scattering, infrared and Raman spectroscopy confirmed that the material no longer consisted of ordered molecular structures, but that carbon and oxygen lay amorphously side by side in a disordered manner. The researchers see a mixture of carbon dioxide with silicon dioxide as a way of maintaining this solid state even at lower pressures. They also want to increase the pressure tests to over 80 gigapascals, because amorphous silicon oxide and germanium oxide change their amorphous structure again under this pressure and the main molecules combine with more than four oxygen molecules.