Hyperfine Energy States: The Untold Story

1
The Hyperfine Spectrum of KI
Our Results Old Potassium eQq -4120 ? 120
kHz Old Iodine eQq -8 5320 2930(v ½) ?
120 kHz New Potassium eQq -4294.65 ? 0.02
(27.34 ? 0.04) (v ½) kHz New Iodine eQq
-85487.639 ? 0.008 (2815.993 ? 0.007) (v ½)
(0.6721 ? 0.0009) J(J1) kHz
Ben McDonald and Charles McEachern Advisor Dr.
James Cederberg Department of Physics, St. Olaf
College Northfield, MN 55057 www.stolaf.edu/people
/molbeam/
Abstract Using St. Olafs molecular beam
electric resonance spectrometer we have done
significant work towards mapping the hyperfine
spectrum of KI. Sufficient progress has been
made that we should be able to improve
preexisting measurements by four to five
significant figures. Additionally, we have begun
to improve upon software written by previous
students.
Our Molecule Previous work on the KI molecule,
which was conducted in the seventies in Germany,
left an uncertainty of around 100 kHz on their
eQq value. Using their work as a starting point,
we have been able to refine those measurements
significantly. Our current level of completion
allows us to calculate the eQq value to within
much less then 1 kHz.

• Why Do This?
• To check quantum theory experimentally
• To increase knowledge of nuclear electric and
  magnetic properties
• To improve the understanding of molecular
  structure

Future Work Once weve gathered a bit more data
for KI, well be able to make some final
revisions to our calculations and then submit
them for publication. Previous work by the
MolBeam group has been published in places such
as the Journal of Chemical Physics. Add
itional work will also be done on translating the
remaining MathCad worksheets to C programs.
This will increase user friendliness as well as
decrease the time it takes to process
data.
Introduction Molecular beam spectroscopy deals
with the amount of energy needed to induce change
in nuclear orientation (spin) within a molecule.
Such spin transitions are called hyperfine
because the energy needed to change spin state is
much less than that required to induce other
transitions, such as vibrational and
rotational. Once these transitions
are induced and fitted, they can be used to
calculate the eQq constant that describes the
shape of the charge distribution within the
nucleus.

• Apparatus
• Three diffusion pumps and two ion pumps evacuate
  the apparatus to 10-7 torr.
• An oven in the source region heats the molecular
  solid to 500 ºC (over 900 ºF), which causes them
  to leave the oven through a small hole.
• A quadrupole lens in region A
• focuses the molecules by
• rotational state into a beam.
• Parallel conducting plates in region C make an
  oscillating electric field which may cause a
  hyperfine transition in the molecules.
• 6. A second lens in region B deflects molecules
  that have undergone a transition.
• 7. A drop in detector current means that there
  was a transition. We pinpoint frequencies where
  this happens.

The Molbeam
Software Development MolBeam students from
previous years have written all the software we
use for data collection and analysis. Much of
this is in MathCad worksheets, and some has
already been rewritten in C. In an effort to
reduce computing time and increase user
friendliness, we are working on creating C
versions of the remaining MathCad programs. The
entire MolBeam group from last summer graduated,
so most of the software work this summer has had
to do with learning C.

Acknowledgments We would like to thank the St.
Olaf College Physics Department, the Whittier
endowment, and the Howard Hughes Medical
Institute for their resources, funding, and the
opportunity to participate in summer research.
Various Nuclear Moments. L to R Quadrupole,
Octuple, Hexadecapole Our work finds the
constants that describe the shape of the charge
and current distributions in the nucleus.