IR spectroscopic observation windows and analysis for environmental issues: application to CO2

Understanding the phenomena that can occur in a given medium necessitates a clear grasp of its chemical composition. In this context, various techniques including infrared (IR) spectroscopy were developed. In this work, we determined the bond force constants of CO2 molecule in gas phase state and trapped in a nanocage by applying group theory to the normal vibrational modes of the symmetric (16O12C16O, 626) and the asymmetric (16O12C18O, 628) CO2 isotopic species. Wilson’s force, F and inverse-mass, G matrices, were calculated for the CO2 (626 and 628) species. The effect of Fermi resonances was included in the analysis. Results are given in terms of bond force constants for stretching and bending modes of CO2 molecule trapped in nanocages of rare gas matrices and of clathrate hydrates. The comparison with the gas phase values demonstrated that the condensed phase effect can be constrained at the harmonic level. A database of vibrational frequencies can then be built from the calculated values with a pseudo-uncertainty range to enhance automatic analysis of observed data pertaining to CO2 in an unknown media by IR sensors. The study of CO2 trapped in nanocages using group theory to calculate force constants has received little theoretical consideration in previous works. Here, we provide an additional approach to evaluate the uncertainty measurement in IR spectroscopy. Similar outcomes should be achievable for other molecules, providing the possibility to improve spectroscopic IR observation and analysis from sensors specially designed for mobile sensing applications. Constrained external degrees of freedom of Carbon Dioxide molecule in a nanocage and anisotropic electric environment perturbing internal vibrational degrees of freedom which have an effect on the infrared signature of the molecule. The calculations show, that the unperturbed v1 mode peaks are at a lower value than the unperturbed 2v2 mode for both the 626 and 628 isotopologues when the molecule is trapped in a rare gas matrix or in a clathrate hydrate nanocage.