Understanding Selectivity in Product Distributions from Laser Ablation of Organic Liquids

Abstract

Pulsed laser ablation in organic solvents is widely used to produce oxide-free metal and metal carbide nanoparticles, often with carbon coatings resulting from laser-induced reactions in the organic solvent. To gain insight into how the molecular structure of the solvent affects these reaction pathways, this work investigates ablation of the C 6 H 14 isomers n-hexane, 2-methylpentane, and 3-methylpentane through characterization of the gas and liquid products with mass spectrometry. Ablation of each C 6 H 14 isomer produces a distinct distribution of product molecular weights and isomers. 2-methylpentane preferentially produces C 3 and C 9 , whereas 3-methylpentane produces C 2 , C 4 , C 8 , and C 10 products. These preferential product distributions, along with the lack of such selectivity in n-hexane, arise from differences in the most favorable C−C bond scission pathways in each C 6 H 14 isomer. Moreover, the particular isomers of C 8 H 18 , C 9 H 20 , C 10 H 22 , and C 12 H 26 produced by ablation of each C 6 H 14 isomer indicate that the vast majority of reaction pathways involve addition reactions between a fragment radical and parent C 6 H 14 or between two C 6 H 14 molecules, without molecular rearrangement. This propensity toward direct addition suggests that the chemical reactions induced by ultrashort pulsed laser ablation proceed on faster time scales than those of radical rearrangements.