Infrared Spectra of Neutral Bent Carbon Dioxide

Ultraviolet spectroscopy of pressurized and supercritical carbon dioxide

Carbon dioxide (CO₂) is prevalent in planetary atmospheres and sees use in a variety of industrial applications. Despite its ubiquitous nature, its photochemistry remains poorly understood. In this work we explore the density dependence of pressurized and supercritical CO₂ electronic absorption spectra by vacuum ultraviolet spectroscopy over the wavelength range 1455-2000 Å. We show that the lowest absorption band transition energy is unaffected by a density increase up to and beyond the thermodynamic critical point (137 bar, 308 K). However, the diffuse vibrational structure inherent to the spectrum gradually decreases in magnitude. This effect cannot be explained solely by collisional broadening and/or dimerization. We suggest that at high densities close proximity of neighboring CO₂ molecules with a variety of orientations perturbs the multiple monomer electronic state potential energy surfaces, facilitating coupling between binding and dissociative states. We estimate a critical radius of ~4.1 Å necessary to cause such perturbations.

Heavy Particle Impact Vibrational Excitation and Dissociation Processes in CO2

A heavy particle impact vibrational excitation and dissociation model for CO₂ is presented. This state-to-state model is based on the forced harmonic oscillator (FHO) theory, which is more accurate than current state-of-the-art kinetic models of CO₂ based on first-order perturbation theory. The first excited triplet state ³B₂ of CO₂, including its vibrational structure, is considered in our model, and a more consistent approach to CO₂ dissociation is also proposed. The model is benchmarked against a few academic zero-dimensional (0D) cases and compared to decomposition time measurements in a shock tube. Our model is shown to have reasonable predictive capabilities, and the CO₂ + O ↔ CO + O₂ reaction is found to have a key influence on the dissociation dynamics of CO₂ shocked flows, warranting further theoretical studies. We conclude this study with a discussion on the theoretical improvements that are still required for a more consistent analysis of the vibrational/dissociation dynamics of CO₂.

Photochemistry of OPN: Formation of Cyclic PON and Reversible Combination with Carbon Monoxide

Cyclic PON, a first 16-electron triatomic ring consisting of two first-row elements, has been generated through 193 nm laser photolysis of OPN in cryogenic matrices. When the photolysis (365 nm) was performed in the presence of CO, OPN combines CO and furnishes an exotic acyclic molecule OPNCO. Upon the 193 nm laser irradiation, OPNCO dissociates mainly to OPN and CO with traces of PN and CO₂ . The identification of cyclic PON and OPNCO with IR spectroscopy is supported by ¹⁵ N-labeling experiments and quantum chemical calculations.