One molecule, composed of the abundant carbon and oxygen atoms, and very stable against dissociation into atoms, is carbon monoxide (CO). The wavelength of the photon emitted when the CO molecule falls from its lowest excited state to its zero energy, or ground, state is 2.6mm, or 115 gigahertz.
One molecule, composed primarily of carbon and oxygen atoms, is very stable and emits a photon with a wavelength of 2.6 millimeters (or 115 gigahertz) when transitioning from its excited state to its ground state.