# Hyperfine structure of the metastable (1s22s2p)P3 states of Be94 and the nuclear electric quadrupole moment

## Abstract

The hyperfine structure (hfs) of Be9(I=32)4 in its metastable (1s22s2p)P23 and P13 atomic states has been measured by the atomic-beam magnetic-resonance method. The zero-field hfs intervals in the P23 state are {Δν(12,32),=187.6157±0.0042Mcsec,}{Δν(32,52),=312. 0226±0.0021Mcsec,}{Δν(52,72),=435.4773±0.0021Mcsec.} The zero-field hfs intervals in the P13 state are {Δν(12,32),=202.9529±0.0015Mcsec,}{Δν(32,52),=354. 4365±0.0027Mcsec.} In order to obtain the dipole and quadrupole coupling constants from the hfs separations, second- and third-order corrections arising from off-diagonal matrix elements of the hyperfine interaction between the P3 fine-structure levels must be included. The values of the hfs interaction constants before and after secondand third-order corrections are: Hfs interaction constant Uncorrected (Mc/sec) Corrected (Mc/sec) A(P23) -124.6167±0.0013 -124.5368±0.0017 B(P23) 0.781 ±0.005 1.429 ±0.008 A(P13) -140.1564±0.0008 -139.373 ±0.012 B(P13) -3.2363±0.0007 -0.753 ±0.044 The individual-electron interaction constants, calculated from the corrected values of A and B, are {as,=-460.2±1.6Mcsec,}{a32,=-12.65±0.54Mcsec,}{b32,=1. 467±0.042Mcsec.} The reason for the larger error limits in the corrected, compared with the uncorrected, numbers is discussed and the experimental values of as and a32 are compared with theory. Measurements of the magnetic field dependence of the hfs lead to the following estimate for the P3 fine-structure separations: {W(P23)-W(P13),=71.86±0.24Gcsec,}{W(P13)-W(P03),=19.41±0.19Gcsec.} From the ratio b32a32 the quadrupole moment, without Sternheimer polarization corrections, is Q=+0.049±0.003 b. Expressions for the third-order corrections to the zero-field hyperfine energies are given, and estimates of the intermediate coupling coefficients c1 and c2 are discussed. © 1967 The American Physical Society.