Pick-Up of Organic Molecules by Mixed Ar Clusters: A Function of Gas Properties and Composition

Clusters present an intriguing field of research, with their properties bridging the gap between an isolated atom/molecule and a bulk. They can act as a substrate for dopant molecules picked up on the fly and located on or inside the cluster. Our research on Ar clusters reveals that gas pressure and composition are crucial parameters determining the pickup probability for molecules such as adenine, uracil, glycine, and ascorbic acid. For pure Ar expansion, the most intense molecular signals are observed in the stagnation pressure range between 10 and 30 bar. Adding up to 33 mol% of He or O₂ at fixed total pressure causes no change in the intensity of dopant and Ar oligomer signals. The addition of N₂O or CO₂ results in a significant intensity drop, with signals from the molecule and Ar oligomers disappearing above 3 mol% of N₂O or CO₂. The opposite effects are observed with the Ar-H₂ mixture at a pressure of 25 bar. Optimal results are obtained for H₂ concentrations between 40 and 50 mol% versus D₂ concentrations between 20 and 35 mol%. Substitution of Ar with an Ar-H₂ mixture causes signal intensities of dopants and Ar oligomers to increase by more than threefold.