Undergrad Is the Spin-Rotation Constant Always Positive in Diatomic Molecules?

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SUMMARY

The spin-rotation constant, denoted as ##\gamma##, can indeed take on negative values in diatomic molecules, contrary to common assumptions. Specifically, in the case of the ground state ##^2\Sigma_+##, examples such as YbF and YbOH demonstrate that ##\gamma## can be negative, influenced by second-order perturbation interactions involving spin-orbit and rotational operators. This indicates that the sign of the spin-rotation constant is dependent on the specific molecular states involved.

PREREQUISITES
  • Understanding of spin-rotation coupling in molecular physics
  • Familiarity with diatomic molecular states, particularly the ##^2\Sigma_+## state
  • Knowledge of second-order perturbation theory in quantum mechanics
  • Experience with spin-orbit interactions in diatomic molecules
NEXT STEPS
  • Research the role of second-order perturbation theory in molecular spectroscopy
  • Study the spin-orbit coupling effects in diatomic molecules like YbF and YbOH
  • Explore the implications of negative spin-rotation constants on molecular behavior
  • Investigate precision measurement techniques in molecular physics
USEFUL FOR

Researchers in molecular physics, quantum chemists, and anyone studying the properties of diatomic molecules and their spin-rotation dynamics will benefit from this discussion.

Malamala
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Hello! Can the spin-rotation constant, ##\gamma##, have a negative value in a diatomic molecule, or does it have to be positive (in my case the state is a ground state ##^2\Sigma_+##, which is about 14000 cm##^{-1}## away from the next electronic level). I don't think I have ever seen negative values for ##\gamma## in the papers I came across, but I am also not sure if there is a reason for it to be always positive. Thank you!
 
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Hello! Sure it can, see for example the YbF and YbOH molecules that are being pursued for precision measurements. In a lot of cases, the spin-rotation constant is mostly determined by a second order perturbation interaction involving spin-orbit and rotational operators. This can be either positive or negative depending on the sorts of states involved.
 
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