Rotational-vibrational Absorption Spectra of CO₂ Molecule in Mid-infrared Region

The energy levels of a molecule depend on the arrangement of consisting atoms, which can be linear, nonlinear, or complex. When atoms in the molecule oscillate and the molecule rotates, the molecule develops fine characteristic energy levels. In this study, we investigated the fine characteristic energy levels of gaseous carbon dioxides using a Fourier transform infrared spectroscopy-type and vacuum-type spectrometer, Vertex 80v (Bruker, Germany). We measured the power spectra of the air in the spectrometer at various vacuum levels. From the measured spectra, we obtained the vibrational and rotational absorption spectra of carbon dioxide. The theoretical and experimental rotation constant (B) values were consistent when the vibrational quantum number of carbon oxides (v) was 0. From the rotation constant obtained at v = 1, we obtained the C-O bonding length. Furthermore, we determined the molar attenuation coefficients of carbon dioxides using Lambert–Beer’s law.