Scalar and quadrupolar intensity contributions in two-photon hyperfine structure transitions in europium

Two-photon transitions from the Eu I ground state 4f ⁷ 6s ² a ⁸ S _7/2 to odd levels with alsoJ=7/2 in the energy range of 34,000 – 36,700 cm^–1 were analysed due to their scalar and quadrupolar contributions. Their ratioR (g, e) were determined experimentally. In most cases the quadrupole contributions are dominant, i.e. 0R (g, e) _exp <>^–3. In the two-photon transition to the level 4f ⁷ 5d ^{2 8} F _7/2 the ratio is remarkably strong:R (g, e) _exp =134 (4)·10^–3. A theoretical estimation ofR (g, e) is not yet satisfying, due to strong configuration mixing in Eu.