UV-ray irradiation never causes amorphization of crystalline CO2: A transmission electron microscopy study

[Display omitted] •Crystallinity of CO2 under UV-ray irradiation was directly observed by TEM.•Amorphization of crystalline CO2 upon UV-ray irradiation was not observed.•Stronger UV-ray irradiation in IR experiments did not cause amorphization either.•UV-fluence expected in molecular clouds will not cause amorphization of CO2 ice. The Crystallinity of ices, amorphous and crystalline, can be altered not only by heat but also by irradiation of UV-rays or charged particles. In this work, the effect of UV-irradiation on the crystallinity of CO2 ice was investigated by using a transmission electron microscope. A crystalline CO2 ice was produced by annealing amorphous CO2 ice. We found that UV-ray irradiation of CO2 crystals at approximately 10 K does not cause amorphization in contrast to the reported amorphization of crystalline water ice below 70 K. We discuss the difference based on the expected UV photochemistry of CO2 ice.