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[40P.15] Laboratory Synthesis of Alcohols and Formic Acid from CO in Astrophysical Ice Analogues: Support for Molecular Formation in the Solid Phase

R. L. Hudson (Eckerd College), M. H. Moore (NASA/Goddard Space Flight Center)

It is now recognized that gas-phase chemistry alone is insufficient to account for the abundances of many interstellar molecules. Low-temperature reactions in the solid state, on interstellar grains or in ice mantles, are likely candidates for molecular formation. Recently we have studied the reactions of hydrocarbons and H atoms in interstellar and cometary ice analogues (\textit{Icarus}, 1997,\textbf{126}, 233). Frozen hydrocarbon+H₂O mixtures were exposed to ionizing radiation near 15 K, and IR spectra of these ices were measured. We found that H-atom addition to acetylene (C₂H₂) occurred, forming ethylene (C₂H₄) and ethane (C₂H₆), and that H- and OH-addition produced acetaldehyde (CH₃C(O)H) and ethanol (C₂H₅OH):

\begin{center} C₂H₂ \;\;arrow\;\; C₂H₄ and CH₃C(O)H \;\;arrow\;\; C₂H₆ and C₂H₅OH \end{center}

We recently have extended these experiments to CO, an abundant interstellar and cometary molecule. Our experiments show that irradiation of CO+H₂O ices reduces CO to CH₃OH (methanol), presumably by H- and OH-addition reactions. Formic acid (HCOOH) and formaldehyde (H₂CO) were observed during these experiments, and appear to be intermediates along the reaction path from CO to CH₃OH:

\begin{center} CO \;\;arrow\;\; H₂CO and HCOOH \;\;arrow\;\; CH₃OH \end{center}

In separate experiments we have confirmed that radiation reduces C₂H₄ and CH₃C(O)H to C₂H₅OH, and HCOOH and H₂CO to CH₃OH. Estimates of product abundances have been made. We conclude that solid-phase H- and OH-addition reactions can contribute to many of the molecules observed in comets and interstellar objects.

The author(s) of this abstract have provided an email address for comments about the abstract: hudsonrl@eckerd.edu

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