Gas phase nucleation is a ubiquitous phenomenon in planetary atmospheres and technical processes, yet our understanding of it is far from complete. In particular, the enhancement of nucleation by the addition of a more volatile, weakly interacting gaseous species to a nucleating vapor has escaped molecular-level experimental investigation. Here, we use a specially designed experiment to directly measure the chemical composition and the concentration of nucleating clusters in various binary CO₂-containing vapors. Our analysis suggests that CO₂ essentially catalyzes nucleation of the low vapor pressure component through the formation of transient, hetero-molecular clusters and thus provides alternative pathways for nucleation to proceed more efficiently. This work opens up new avenues for the quantitative assessment of nucleation mechanisms involving transient species in multicomponent vapors.

气相成核是行星大气和技术过程中普遍存在的现象，但我们对它的理解还远远不够。尤其是，通过向成核蒸气中添加挥发性更高，相互作用较弱的气态物质来增强成核作用已经摆脱了分子水平的实验研究。在这里，我们使用专门设计的实验来直接测量各种包含CO ₂的二元蒸气中的化学成分和成核簇的浓度。我们的分析表明，CO ₂通过形成瞬态，杂分子簇，基本上催化了低蒸气压组分的成核，从而为成核提供了更有效的替代途径。这项工作为定量评估涉及多组分蒸气中瞬态物质的成核机理开辟了新途径。