Abstract
In this thesis the unimolecular hydrogen transfer reactions (H-shift) in peroxy and acyl peroxy
radicals derived from the atmospheric oxidation of volatile organic compounds (VOC) have been
investigated. A unimolecular isomerization reaction where a hydrogen atom is moved internally
within a radical is denoted as a H-shift reaction. Quantum chemical calculations were carried out to
investigate the potential energy surface of the H-shift reactions and the subsequent decomposition
pathways. The transition state theory including the Eckart quantum tunneling correction have been
used to calculate the reaction rate constants of the H-shift reactions.
The autoxidation of volatile organic compounds is an important oxidation mechanism that produces
secondary organic aerosols (SOA) and recycles hydroxyl (OH) radicals. The autoxidation cycle
produces a second generation peroxy radical (OOQOOH) through a series of H-shift reactions and
O2 attachments. I have investigated the H-shift reactions in two OOQOOH radicals (hydroperoxy
peroxy radicals and hydroperoxy acyl peroxy radicals). The H-shift reaction rate constants have
been compared with the bimolecular reaction rate constants of the peroxy radicals to assess the
atmospheric impact of the investigated H-shift reactions. The H-shift reactions from a hydroperoxy
(OOH) group are observed to be rapid with reaction rate constants above 103 s-1. The H-shift
reaction from an OOH group is, in this thesis, shown to be very important in the atmospheric
autoxidation of VOCs. Thus H-shift reactions from an OOH group should be considered when the
autoxidation of VOCs is investigated.
Furthermore, I have investigated the atmospheric impact of H-shift reactions in the peroxy radicals
derived from the oxidation of the 2-methyl-3-buten-2-ol (MBO232) molecule. MBO232 is an
important biogenically emitted VOC that produces SOA. I used the GEOS-Chem model to simulate
the atmospheric impact of the H-shift reactions in the MBO232 peroxy radical. I have observed that
the H-shift reactions are of minor importance in the atmosphere and that the production of epoxides
through the alcoholic H-shift reactions is unlikely. Finally, I have observed that the M06-2X/augcc-
pVTZ and wB97X-D/aug-cc-pVTZ methods calculate H-shift reaction rate constants that are
comparable to single-point ROHF-CCSD(T)-F12a/cc-pVDZ-F12 calculations.
radicals derived from the atmospheric oxidation of volatile organic compounds (VOC) have been
investigated. A unimolecular isomerization reaction where a hydrogen atom is moved internally
within a radical is denoted as a H-shift reaction. Quantum chemical calculations were carried out to
investigate the potential energy surface of the H-shift reactions and the subsequent decomposition
pathways. The transition state theory including the Eckart quantum tunneling correction have been
used to calculate the reaction rate constants of the H-shift reactions.
The autoxidation of volatile organic compounds is an important oxidation mechanism that produces
secondary organic aerosols (SOA) and recycles hydroxyl (OH) radicals. The autoxidation cycle
produces a second generation peroxy radical (OOQOOH) through a series of H-shift reactions and
O2 attachments. I have investigated the H-shift reactions in two OOQOOH radicals (hydroperoxy
peroxy radicals and hydroperoxy acyl peroxy radicals). The H-shift reaction rate constants have
been compared with the bimolecular reaction rate constants of the peroxy radicals to assess the
atmospheric impact of the investigated H-shift reactions. The H-shift reactions from a hydroperoxy
(OOH) group are observed to be rapid with reaction rate constants above 103 s-1. The H-shift
reaction from an OOH group is, in this thesis, shown to be very important in the atmospheric
autoxidation of VOCs. Thus H-shift reactions from an OOH group should be considered when the
autoxidation of VOCs is investigated.
Furthermore, I have investigated the atmospheric impact of H-shift reactions in the peroxy radicals
derived from the oxidation of the 2-methyl-3-buten-2-ol (MBO232) molecule. MBO232 is an
important biogenically emitted VOC that produces SOA. I used the GEOS-Chem model to simulate
the atmospheric impact of the H-shift reactions in the MBO232 peroxy radical. I have observed that
the H-shift reactions are of minor importance in the atmosphere and that the production of epoxides
through the alcoholic H-shift reactions is unlikely. Finally, I have observed that the M06-2X/augcc-
pVTZ and wB97X-D/aug-cc-pVTZ methods calculate H-shift reaction rate constants that are
comparable to single-point ROHF-CCSD(T)-F12a/cc-pVDZ-F12 calculations.
| Original language | English |
|---|
| Publisher | Department of Chemistry, Faculty of Science, University of Copenhagen |
|---|---|
| ISBN (Print) | 978-87-91963-70-4 |
| Publication status | Published - 2016 |