A spectroscopic study on some atmospherically relevant reactions with the support of electronic structure calculations

Abstract

The work described in this thesis is a study of the atmospherically relevant reactions of
dimethyl sulfide (DMS) with halogen and interhalogen molecules (Cl2, Br2, I2, BrCl and
ICl) and ozone with selected alkenes (ethylene, tetramethylethylene and 2-methylpropene).
The aim was to investigate the mechanisms of these reactions and identify reaction inter-
mediates.

Infrared matrix isolation spectroscopy and u.v.-photoelectron spectroscopy were used to
detect intermediates and products, and ab initio calculations were used to facilitate spec-
tral assignments and to provide information on the structure of the molecules studied.
The results confirm and extend previous matrix isolation infrared studies on the DMS/Cl2
system and also provide vibrational assignment and ab initio calculations for the electronic
structure of the intermediates present in the related DMS/Br2, DMS/I2, DMS/BrCl and
DMS/ICl reactions. For all systems, the intermediate is shown to be a van der Waals
complex of the type DMS:XY, where XY is a halogen or interhalogen molecule.

The reactions of ozone and alkenes were studied by u.v.-photoelectron spectroscopy. The
results follow the general mechanism proposed by Criegee but no Criege intermediate is
observed. Reaction mechanisms are presented and discussed for each reaction investi-
gated.

Of great importance is the observation of the first excited state of oxygen (O2 a1 ? g) in
the reactions of ozone with ethylene and 2-methylpropene which play an important role
in the oxidation chemistry of the troposphere.

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Identifiers

ORCID for John Dyke: orcid.org/0000-0002-9808-303X

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