DPS Meeting, Madison, October 1998
Session 40P. Comets I, II, III
Contributed Poster Session, Wednesday, October 14, 1998, 5:10-6:10pm, Hall of Ideas

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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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