Vapor Pressures of Low-Temperature C2Hx Hydrocarbon Ices

Grundy, W.G. and Tan, S.P. and Steckloff, J.K. and Smith, A.S. and Lucas, T.M. and Lindberg, G.E. and Brand, M.D. and Tegler, S.C. and Thieberger, C.L. and Knudsen, I.E. and Hanley, J. Vapor Pressures of Low-Temperature C2Hx Hydrocarbon Ices. Icarus. (In Press)

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Abstract

Ethane (C2H6), ethylene (C2H4), and acetylene (C2H2) are cosmically abundant hydrocarbons with two carbon atoms. They play important roles in a variety of astrophysical settings from sublimation of cometary ices, to photolytic haze formation in the upper atmospheres of Titan and Pluto, to formation of Charon’s dark reddish polar cap, to chemical evolution of protoplanetary nebulae. Temperature-dependent vapor pressures and latent heats of sublimation of these species at relevant temperatures are needed to accurately model the processes involved. We used a quartz crystal microbalance to make new measurements of the sublimation rates of these hydrocarbon ices at low temperatures and pressures relevant to diverse environments. Our method accounts for simultaneous sublimation from and condensation onto the quartz crystal. We find vapor pressures of C2H6 and C2H4 ices to be similar to previous estimates in the literature, while the vapor pressure of C2H2 is much lower, owing to the existence of a second, lower temperature solid phase stable below 133 K. We also provide updated parameters for ices of N2, CO, CH4, O2, and NH3 that we had previously published, applying a new correction to account for condensation from other cold parts of the apparatus.

Item Type:	Article
Keywords:	Ices Planetary material thermodynamics Experimental Techniques Hydrocarbons
Subjects:	Q Science > QB Astronomy Q Science > QC Physics Q Science > QD Chemistry
NAU Depositing Author Academic Status:	Faculty/Staff
Department/Unit:	College of the Environment, Forestry, and Natural Sciences > Physics and Astronomy
Date Deposited:	01 Jun 2026 15:37
Last Modified:	01 Jun 2026 15:37
URI:	https://openknowledge.nau.edu/id/eprint/6360

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