Carbon dioxide ice caps, glaciers and seawater. It is present in deposits of petroleum and natural gas. Carbon dioxide is odorless at normally encountered concentrations. However, at high concentrations, it has a sharp and acidic odor. As the source of available carbon in the carbon cycle, atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena. Plants, algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a waste product. It
Carbon dioxide stretching mode at 1388 cm which is only observed in the Raman spectrum. Carbon dioxide is soluble in water, in which it reversibly forms (carbonic acid), which is a weak acid since its ionization in water is incomplete. The hydration equilibrium constant of carbonic acid is formula_1 (at 25 °C). Hence, the majority of the carbon dioxide is not converted into carbonic acid, but remains as molecules, not affecting the pH. The relative concentrations of , and the deprotonated forms (bicarbonate) and (carbonate) depend on the pH. As shown in a Bjerrum plot, in neutral or slightly alkaline water (pH