Infrared absorption spectra analysis for optical detection of ¹⁴CO₂

Abstract Spectral measurements of radiocarbon dioxide ( 14 CO 2 ) require accurate knowledge of both the line positions and intensities. Our paper analyzes the absorption characteristic of 14 CO 2 for optical detection in middle infrared range theoretically. By studying the distribution and properties of 14 CO 2 absorption spectra under the interfering of others gas, it can be found that the isotopes of carbon dioxide (CO 2 , such as 13 CO 2 , 16 O 13 C 18 O, 16 O 13 C 17 O) and atmospheric gases (such as nitrous oxide (N 2 O) and ozone (O 3 )) exhibit interference with the absorption spectra of 14 CO 2 . They cannot be chemically removed from CO 2 sample gas but can be suppressed by reducing the sample temperature. The (00011–00001) P(20) in the P-branch of the strong spectral absorption V 3 band of 14 CO 2 , is a suitable absorption peak for spectral probing. If the sample gas is cooled to 172.5 K, the absorption interference by other isotopes such as 13 C 16 O 2 can be suppressed. At the same time, to avoid the interference of the absorption tail line from other atmospheric gases, the pressure condition of 0.01 atm is necessary. Our results provide critical insights into the optimization of spectral measurement conditions for 14 CO 2 , which is an important reference for improving the accuracy and reliability of optical detection methods in middle infrared range.