Analysis of the Rotational Structure of CO₂ by FTIR Spectroscopy

Abstract

A physical chemistry experiment is described that involves the determination of some spectroscopic parameters of carbon dioxide, a molecule that obeys Bose-Einstein statistics. The main advantage of this experiment is that the spectra are easily recorded, not requiring a gas cell, because the sensitivity and resolution of conventional FTIR spectrometers is good enough to record spectra with a high signal-to-noise ratio and good resolution of the fine rotational structure. From the rotational lines of the antisymmetric stretching band, the moments of inertia and the bond lengths of CO₂ in the fundamental and the first-excited state can be accurately obtained. The particular case that carbon dioxide represents helps students understand the restrictions that symmetry and statistics impose on some molecules and the consequences that they have on the absorption of radiation.