Giant Dipole Resonance inHe4with Noncentral Forces and Target-Recoil Corrections

The ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ giant dipole resonance is calculated with a continuum shell model which treats the center of mass correctly and includes possible noncentral components of the nucleon-nucleon interaction. The ($\gamma$,$p$) and ($\gamma$,$n$) cross sections and asymmetry coefficients agree well with the experiment. The $b_2$ asymmetry coefficient is shown to depend on the spin-orbit odd component of the effective nuclear force. The $1^{-}$ level positions and channel mixing are in best agreement with "solution II" of the $R$-matrix fit of Werntz and Meyerhof.