Determining the electric quadrupole moments of gas molecules from measurements of
birefringence induced in the gas by an applied electric field gradient is widely recognised
as being the most direct experimental technique for this purpose. This thesis presents
a new molecular theory of the experiment, and also describes the apparatus used in
the measurement of the quadrupole moments of a number of gases and the revisions
made to the manner in which the experiment was performed.
A recent eigenvalue theory of light propagation in matter has been used to derive an
expression relating the induced birefringence to the electric quadrupole moment of the
molecule, whether this be dipolar or not. This expression is different from that which
has previously been applied to dipolar molecules. It is shown that the new expression
is independent of molecular origin only if it is cast in terms of the primitive quadrupole
moment, as opposed to the traceless moment.
Previous work using the same set of apparatus yielded results for carbon dioxide
which were significantly lower than those reported by other workers. By using the Jones
calculus to re-examine the cascade of optical components used in the experiment, it
was found that the previous method of performing the experiment did not completely
eliminate the effects of an imperfect retardance in the quarter-wave plate used, nor of
strain-induced birefringence in the windows of the the cell containing the gas. These
effects could cause results to be underestimated by as much as 8%. It is shown that
a better method of performing the experiment is to amplify the optical signal by deliberately
offsetting the analysing prism, rather than the quarter-wave plate as was
previously done.
The results of measurements made using this technique are reported for carbon
dioxide, carbon monoxide, nitrogen, ethene, chlorine, and boron trifluoride. The measured
quadrupole moment of carbon dioxide is in good agreement with the most recent
values found by other workers using a similar experiment, and with the latest theoretical
value of this quantity. / Thesis (PH.D.)-University of Natal, Pietermaritzburg, 1993.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/7798 |
| Date | January 1993 |
| Creators | Imrie, David Alexander. |
| Contributors | Raab, R. E., Graham, C. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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