The hyperfine structure coupling constants of the ground
3
P multiplet of
17
O have been measured in a paramagnetic resonance experiment with a sample of enriched oxygen gas. They are:
a
2
= – 218.569 ± 0.004 Mc/s,
a
1
= 4.738 ± 0.036 Mc/s,
a
2,1
= –126.6 ± 2.0 Mc/s,
a
1,0
= – 91.7 ± 7.2 Mc/s,
b
2
= –10.438 ± 0.030 Mc/s,
b
1
= 5.199 ± 0.090 Mc/s. These results confirm the values of
a
2
and
b
2
reported previously by Kamper, Lea & Lustig 1957. Measurements have also been made on the excited level of the ground
2
P
multiplet of
19
F. They yield:
a
½
= 10244.21 ± 0.03 Mc/s,
g
J
(
J
= ½) = 0.66561 ± 0.00003. An analysis of the magnetic hyperfine constants in the ground multiplets of
17
O and
19
F shows that in neither case do they yield consistent values for the two parameters <
r
-3
> and |
ψ
(0)|
2
usually associated with magnetic hyperfine structure. All measurements of hyperfine structure in these multiplets are consistent, however, with the requirements of
LS
coupling theory which introduce a third parameter into the magnetic hyperfine operator. The discrepancy is attributed to polarization effects, other than spin polarization of the core
s
electrons, brought about by the exchange interaction between electrons.