NMRON studies for the \+/-3] --> \+2] Mn-54 transitions in antiferromagneti
c MnBr2 . 4H(2)O, in the millikelvin regime, are presented and discussed. N
ew values are given for (i) the sum of the effective molecular exchange and
magnetic anisotropy fields acting on the Mn2+ ions, B-E(eff) + B-A = 2.23(
2) T, and (ii) the magnetic dipole hyperfine splitting, A = -201.99(1) MHz,
electric quadrupole hyperfine splitting P = 0.049(8) MHz and pseudoquadrup
ole splitting P' = 1.63(2) MHz for the Mn-54 nuclei.