FORBIDDEN ROTATION TRANSITIONS BETWEEN NUCLEAR SPIN MODIFICATIONS IN POLYATOMIC MOLECULES BY NUCLEAR SPIN-ROTATION INTERACTIONS
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Date
1987
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Ohio State University
Abstract
The nuclear spin-rotation interaction Hamiltonian of polyatomic molecules with different symmetries has been derived with respect to the molecule-fixed axes. Terms diagonal in the basis set | IJFMF) cause nuclear hyperfine structure whereas the off-diagonal ones give rise to the conversion between different nuclear spin states. The basic difference between them is the symmetry upon permuting the spin coordinates of identical nuclei. Based on Wigner's idea on the stability of ortho- and para- hydrogen,1 a group theoretical method is developed to discriminate the diagonal terms from the off-diagonal ones. We use an extended group in which pure nuclear permutation operations are added to the usual molecular symmetry group. The diagonal terms are totally symmetric to these added operations while the non-diagonal terms are not. Van Vleck's reverse angular momentum method2 has been applied to evaluate the off-diagonal matrix elements. We estimate the order of magnitude of the conversion rate3 due to this interaction and discuss some experimental observations.
Description
$^{1}$ Wigner, E.P. Z. Phys. Chem. B 1933, 23, 28 $^{2}$ Van Vleck, J.H. Revs. Mod. Phys. 1951, 23, 213 $^{3}$ Curl, Jr., R.F., Kasper, J.V.V., and Pitzer, K.S. J. Chem. Phys 1967, 46, 3220
Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of Chicago; Department of Physics, India Institute of Technology
Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of Chicago; Department of Physics, India Institute of Technology