In the gas phase, carbon dioxide molecules undergo significant vibrational motions and do not keep a fixed structure. The symmetric stretching mode does not create an electric dipole so is not observed in IR spectroscopy, but it is detected in by Raman spectroscopy at 1388 cm −1 (wavelength 7.2 μm). Some of the vibrational modes are observed in the infrared (IR) spectrum: the antisymmetric stretching mode at wavenumber 2349 cm −1 (wavelength 4.25 μm) and the degenerate pair of bending modes at 667 cm −1 (wavelength 15 μm). When a molecule touches a surface or touches another molecule, the two bending modes can differ in frequency because the interaction is different for the two modes. There are two bending modes, which are degenerate, meaning that they have the same frequency and same energy, because of the symmetry of the molecule. In the symmetric and the antisymmetric stretching modes, the atoms move along the axis of the molecule. Lower line: degenerate pair of bending modes.Īs a linear triatomic molecule, CO 2 has four vibrational modes as shown in the diagram. Stretching and bending oscillations of the CO 2 carbon dioxide molecule. It has a sharp and acidic odor and generates the taste of soda water in the mouth, but at normally encountered concentrations it is odorless. It is a byproduct of fermentation of sugars in bread, beer and wine making, and is added to carbonated beverages like seltzer and beer for effervescence. Sequestered CO 2 is released into the atmosphere through burning fossil fuels or naturally by volcanoes, hot springs, geysers, and when carbonate rocks dissolve in water or react with acids.ĬO 2 is a versatile industrial material, used, for example, as an inert gas in welding and fire extinguishers, as a pressurizing gas in air guns and oil recovery, and as a supercritical fluid solvent in decaffeination of coffee and supercritical drying. CO 2 is eventually sequestered (stored for the long term) in rocks and organic deposits like coal, petroleum and natural gas. These sinks can become saturated and are volatile, as decay and wildfires result in the CO 2 being released back into the atmosphere. About half of excess CO 2 emissions to the atmosphere are absorbed by land and ocean carbon sinks. Since plants require CO 2 for photosynthesis, and humans and animals depend on plants for food, CO 2 is necessary for the survival of life on earth.Ĭarbon dioxide is 53% more dense than dry air, but is long lived and thoroughly mixes in the atmosphere. CO 2 is released from organic materials when they decay or combust, such as in forest fires. In turn, oxygen is consumed and CO 2 is released as waste by all aerobic organisms when they metabolize organic compounds to produce energy by respiration. Plants, algae and cyanobacteria use energy from sunlight to synthesize carbohydrates from carbon dioxide and water in a process called photosynthesis, which produces oxygen as a waste product. Its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by organisms and geological phenomena. Burning fossil fuels is the primary cause of these increased CO 2 concentrations and also the primary cause of climate change.
It is a trace gas in Earth's atmosphere at 421 parts per million (ppm), or about 0.04% by volume (as of May 2022), having risen from pre-industrial levels of 280 ppm. When carbon dioxide dissolves in water, it forms carbonate and mainly bicarbonate ( HCO −ģ), which causes ocean acidification as atmospheric CO 2 levels increase.
Carbon dioxide is soluble in water and is found in groundwater, lakes, ice caps, and seawater. In the air, carbon dioxide is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. It is found in the gas state at room temperature, and as the source of available carbon in the carbon cycle, atmospheric CO 2 is the primary carbon source for life on Earth. Carbon dioxide ( chemical formula CO 2) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms.
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