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Dark cloud modeling for the ortho-to-para abundance ratio of the cyclic C 3 H 2

by Park, In Hee

Abstract (Summary)
We present the first attempt to model the ortho-to-para abundance ratio (hereafter o/p ) of c-C 3 H 2 so as to reproduce its observed ratio in cold dense clouds. According to observations for TMC-1 (a quiescent, starless core), TMC-1C (a prestellar core) and L1527 (a protostellar core), the o/p -C 3 H 2 ratio is 2.4 - 2.7, a value which is only slightly lower than the statistical ratio of 3 pertaining to high temperature equilibrium. In order to model the ortho-to-para abundance ratio, we used a large network of chemical reactions augmented by reactions that specifically consider the formation and depletion of ortho and para forms of the molecules c-C 3 H 2 and c-C 3 H 3 ^+ . The reaction branchfractions were determined by a variety of considerations. We then investigated the sensitivity of the calculated ortho-to-para ratio for c-C 3 H 2 to a number of factors such as time, density, elemental C/O ratio, the depletion of metals from the gas, and the cosmic ray ionization rate. While these parameters can affect the calculated ratio, the major factor appears to be the choice of branching fractions for the neutral products of the C 3 H 3 ^+ + e - dissociative recombination reaction. In particular, in order to reproduce the o/p -C 3 H 2 ratio, it is necessary that the product channel C 3 H 2 + H be the dominant one.
Bibliographical Information:

Advisor:

School:The Ohio State University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:chemical modeling molecular abundances processes

ISBN:

Date of Publication:01/01/2005

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