1 Vapor-phase nucleation of n-pentane, n-hexane, and n-heptane: Critical cluster properties Kehinde E. Ogunronbi, a and Barbara E. Wyslouzil a,b,* a William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, Ohio 43210, USA. b Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA *wyslouzil.1@osu.edu ABSTRACT The first and second nucleation theorems provide a way to determine the molecular content and excess internal energies of critical clusters, that relies solely on experimental nucleation rates measured at constant temperatures and supersaturations, respectively. Here we report the size  ∗ and excess internal energy   ( ∗ ) of n-pentane, n-hexane, and n-heptane critical clusters when particles form under the highly supersaturated conditions present in supersonic expansions. In summary, critical clusters contain from ~2 to ~11 molecules and exhibit the expected increase in critical cluster size with increasing temperature and decreasing supersaturation. Surprisingly, the  ∗ values for all three alkanes appear to lie along a single line when plotted as a function of supersaturation. Within the framework of the capillarity approximation, the excess internal energies determined for the n-heptane critical clusters formed under the low temperature (~ 150 K) conditions in our supersonic nozzle are reasonably consistent with those determined under higher temperature (~ 250 K) conditions in the thermal diffusion cloud chamber by Rudek et al. [J. Chem Phys. 105, 4707 (1996)]. This is the author’s peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset. PLEASE CITE THIS ARTICLE AS DOI: 10.1063/1.5123284