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DESCRIPTION:Art Brill\, UVA\n\nH_{2}N has one unpaired electron and
three nuclei of non-zero spin. The four H_{2}N isotopes from 1H\, ^{2}H\, ^{14}N and ^{15}N have corres
ponding sets of hyperfine interactions. Measurements of these constrain c
alculations of electronic wavefunctions and energies\, and provide basic k
nowledge for application to more complex systems. Nuclear spin-state mixi
ng arises from the off-diagonal elements of the nuclear energy matrix\, e.
g. M_{xx} ≡\; σ\;κ\; 〈\;ψ\;|Σ\; (S_{k
z}x^{2}_{kn/}r^{5}_{kn }+ S_{k'zx2k'n/r5k'n|Ψ\;〉\
; (Airne and Brill\, Phys. Rev.A 63 052511). The principle hyperfine A-va
lues can be expressed in terms of the M’s\, e.g. Azz = A
Fermi - (4/3σ\;)( Mxx + Myy - 2 Mzz)\, the
reby simplifying the energy matrices. In the absence of nuclear spin-stat
e mixing (i.e. each state pure mI) there are\, e.g. 10 epr tran
sitions in D215N and 15 in D214N\, all Δ\;mI = 0 fully allowed. In the presence of mixin
g there are 243 in D215N and 729 in D214N\, with large differences in probability among transitions. Be
cause of numerous\, at least partially allowed\, overlapping transitions\,
useful information can be obscured in H2N magnetic resonance s
pectra. Research is required to arrive at effective experimental conditio
ns. The wide range of transition probabilities will cause H2N
resonances to exhibit a corresponding range of microwave power saturation
behavior. Simulations display remarkable effects which call for experimen
tal verification by employing a wide range of powers. The nuclear Zeeman
interaction (proportional to B) perturbs both the energy and state mixing
of nuclear levels\, thereby affecting the separation and probability of re
sonances. Of special interest are the fields Bcross at which p
airs of hyperfine levels draw closest. A spectrometer with microwave freq
uency scanning at fixed B would be useful for centers like H2N
in which on-diagonal hyperfine energy matrix elements depend significantly
upon B.
DTSTART:20060120T210000Z
LOCATION:Physics Building\, Room 204
SUMMARY:Nuclear Spin-Electron Spin Interactions in the Three-Atom System H<
sub>2}N
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