On the formation of small molecules
by radiative association
Sergey V. Antipov
Department of Chemistry and Molecular Biology
Faculty of Science
Thesis for the Degree of Doctor of Philosophy in Natural Science
specializing in Chemistry. The thesis will be presented and defended on
Monday March 18th, 2013, at 10:15 in room 10:an, Kemigården 4, Gothenburg.
ISBN: 978-91-628-8650-9
Abstract
This thesis is devoted to the theoretical investigation of radiative association, which is
one of the processes contributing to formation of molecules in the interstellar
medium. The formation of the CN, SiN, SiP and CO molecules through radiative
association of the corresponding atoms in their ground electronic states is studied by
the means of classical and quantum dynamical calculations. In all cases the Born–
Oppenheimer approximation is employed. The corresponding rate coefficients are
calculated and the Breit–Wigner theory is used to properly account for the resonance
contributions.
Some common features of the radiative association process for the considered systems
are discovered. For example, a drop in magnitude of the cross sections at high energy
and, consequently, the high-temperature rate coefficients is observed. Also, is is
shown that in the absence of a potential barrier the semi-classical formalism provides
a good estimate for the rate coefficients.
A pronounced isotope effect is discovered for the formation of CO by radiative
association of C(3P) and O(3P) atoms. It is shown that the presence of a potential
barrier on the A1Π electronic state of carbon monoxide leads to different formation
channels for the 12CO and 13CO isotopologues at low temperatures.
The role of spin-orbit and rotational couplings in radiative association of C(3P) and
N(4S) atoms is investigated. Couplings among doublet electronic states of the CN
radical are considered, giving rise to a 6-state model of the process. Comparison of
the energy-dependent rate coefficients calculated with and without spin-orbit and
rotational couplings shows that these have a strong effect on the resonance structure
and low-energy baseline of the rate coefficient.
KEYWORDS: molecule formation, diatomics,
resonances, cross sections, rate coefficients
radiative
association,
ISBN: 978-91-628-8650-9