To investigate the formation mechanisms of CO2 clathrate hydrate under vacuum conditions, infrared spectra of vapor-deposited H2O-CO2 amorphous ice were measured. From analyses of variations in the spectral features with warming, remarkable changes were found at similar to 100 K. The results indicate that the deposited amorphous ice is transformed into CO2 clathrate hydrate at around similar to 100 K. From the results, a phase diagram of CO2 clathrate hydrate from vapor deposited amorphous ice was predicted. The results suggest the existence of pure CO2 clathrate hydrates in space.