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Chemical Evolution of Dense Clouds

Published online by Cambridge University Press:  14 August 2015

E. W. Chapelle ,
B. D. Donn ,
W. A. Payne Jr.  and
L. J. Stief
E. W. Chapelle
Affiliation:
Astrochemistry Branch, Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Md. 20771, U.S.A.
B. D. Donn
Affiliation:
Astrochemistry Branch, Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Md. 20771, U.S.A.
W. A. Payne Jr.
Affiliation:
Astrochemistry Branch, Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Md. 20771, U.S.A.
L. J. Stief
Affiliation:
Astrochemistry Branch, Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Md. 20771, U.S.A.

Abstract

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Thermal reactions largely determine the chemical evolution of interstellar molecules during various phases associated with the evolution of interstellar clouds. A similar mechanism may be the source of the array of observed polyatomic molecules. If astronomical time scales are comparable to or less than chemical time scales, thermodynamic equilibrium will not be attained. Other factors also affect the validity of thermodynamic calculations of molecular composition. An experimental investigation of thermal reactions in a simplified system is under way. Preliminary results of the HCN–H2 reaction at 1000 K indicate reaction times of several hours. These have been extrapolated to lower temperatures and fitted to models of the primordial solar nebula, proto stars and red giants. In these situations equilibrium would generally not be attained and reaction products would freeze out at temperatures near 700 K or greater.

Type
Part VII Molecules, Theory and Observations
Information
Symposium - International Astronomical Union , Volume 52: Interstellar Dust and Related Topics , 1973 , pp. 387 - 393
Copyright
Copyright © Reidel 1973 

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