Nuclear Spectroscopy in theαParticle

We discuss the properties of the 15-dimensional $\mathrm{SU}\left(4\right)\mathrm{}$ supermultiplet of negative-parity excited states of the $A=4\mathrm{}$ system. This multiplet consists of the electric-dipole resonance and its spin-isospin analogs. The position of the "center of gravity" of this supermultiplet is determined by the Wigner and Majorana components of the nucleon-nucleon force, while the splittings within the supermultiplet are due to the spin-dependent parts of the force. We calculate the energies and state vectors of these levels within the framework of the shell model after isolating the center-of-mass motion and assuring ourselves that we are dealing with proper intrinsic excitations of the system. We compute the position of the "center of gravity" of the supermultiplet and the splittings within it,u sing both a Kurath force and a force taken from low-energy nucleon-nucleon scattering. The results are compared with some recent experimental findings concerning these levels.