Fragmentation of stretched spin strength inSi28

Calculations have been made to explore the effect of configuration mixing in a large basis on the fragmentation of the ‘‘stretched’’ M6 strength in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$. Our work extends a previous calculation, which allowed a single particle in the $f_{7/2}$ orbit and the remainder in the (unrestricted) 1$d_{5/2}$ and 2$s_{1/2}$ orbits, by also allowing up to four particles in the 1$d_{3/2}$ orbit. It is found that configuration mixing within this expanded basis gives an improved description of the spectrum and several other properties of the observed states.