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.

二氧化碳 (CO ₂ ) 在行星大气中普遍存在，并可用于各种工业应用。尽管它无处不在，但人们对它的光化学仍然知之甚少。在这项工作中，我们通过真空紫外光谱在 1455-2000 Å 波长范围内探索加压和超临界 CO _{2电子吸收光谱的密度依赖性。}我们表明，最低吸收带跃迁能量不受密度增加达到和超过热力学临界点（137 巴，308 K）的影响。然而，光谱固有的扩散振动结构的幅度逐渐减小。这种效应不能仅通过碰撞加宽和/或二聚化来解释。我们建议在高密度下靠近邻近的 CO_{具有多种取向的2}分子扰乱了多个单体电子态势能面，促进了结合态和解离态之间的耦合。我们估计引起此类扰动所需的临界半径约为 4.1 Å。