Space-filling models of the carbon dioxide molecule

Carbon dioxide is colorless. At low concentrations the gas is odorless; however, at sufficiently high concentrations, it has a sharp, acidic odor. As a linear triatomic molecule, carbon dioxide has four vibrational modes as shown in the diagram. In the symmetric and the antisymmetric stretching modes, the atoms move along the axis of the molecule. 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. 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. Some of the vibrational modes are observed in the infrared spectrum: the antisymmetric stretching mode at wavenumber 2349 per centimeter and the degenerate pair of bending modes at 667 per centimeter. The symmetric stretching mode does not create an electric dipole so is not observed in infrared spectroscopy, but it is detected in by Raman spectroscopy at 1388 per centimeter. In the gas phase, carbon dioxide molecules undergo significant vibrational motions and do not keep a fixed structure. Contributor: Junjie Chen, ORCID: 0000-0001-5055-4309, E-mail address: [e-mail], Department of Energy and Power Engineering, School of Mechanical and Power Engineering, Henan Polytechnic University, 2000 Century Avenue, Jiaozuo, Henan, 454000, P.R. China