Abstract
This thesis presents computational studies of both the static and dynamic parameters
of the nuclear magnetic resonance (NMR) spectroscopy of gaseous xenon.
First, state-of-the-art static magnetic resonance parameters are computed in small
xenon clusters by using methods of quantum chemistry, and second, time-dependent
relaxation phenomena are investigated via molecular dynamics simulations
at different experimental conditions. Based on the underlying quantum and
classical mechanics concepts, computational methods represent a procedure complementary
to experiments for investigating the properties of atoms, molecules,
clusters and solids.
Static NMR spectral parameters, chemical shift, shielding anisotropy and asymmetry
parameter, nuclear quadrupole coupling, and spin-rotation coupling, are
calculated using different electronic structure methods ranging from the uncorrelated
Hartree-Fock method to correlated second-order Møller-Plesset many-body
perturbation, complete/restricted active space multiconfiguration self-consistent
field, and to coupled-cluster approaches. The bond length dependence of these
properties is investigated in the xenon dimer (Xe2). A well-characterized property
in experimental NMR, the second virial coefficient of nuclear shielding, is
theoretically calculated by a variety of methods and convincingly verified against
experimental findings. Here, it is mandatory to include effects from special relativity
as well as electron correlation. As a side result, a purely theoretical potential
energy curve for Xe2, comparable to best experimental ones, is calculated.
A pairwise additive scheme is established to approximate the NMR properties in
differently coordinated sites of xenon clusters Xen (n = 2 - 12). Especially the
pairwise additive chemical shift values are found to be in close agreement with
quantum-chemical results and only a small scaling factor close to unity is needed
for the correct behavior. Finally, a dynamical magnetic resonance property, the
experimental nuclear spin-lattice relaxation rate R1 of monoatomic Xe gas due to
the chemical shift anisotropy (CSA) mechanism is validated from first principles.
This approach is based on molecular dynamics simulations over a large range of
temperatures and densities, combined with the pairwise additive approximation
for the shielding tensor. Therein, the shielding time correlation function is seen
to reflect the characteristic time scales related to both interatomic collisions and
cluster formation. For the first time, the physics of gaseous xenon is detailed in
full in the context of CSA relaxation.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn978-951-42-9457-0 |
| Date | 28 May 2011 |
| Creators | Hanni, M. (Matti) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 2011 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/1239-4327 |
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