Clarifying the N,Z=14 Shells near the Drip Lines from the Spectroscopy of ^{22}Si and ^{21}Al.

Evidence for a (sub)-shell closure at Z=14 has been observed from the spectroscopy of ^{22}Si and ^{21}Al. Using a fast ^{23}Si beam on a ^{9}Be target, several proton-decaying resonances have been populated in ^{21}Al and ^{22}Si, including the first measurement of the 2_{1}^{+} state in ^{22}Si with an excitation energy of 2.352(55) MeV. Relative to the known N=14 subshell closure in ^{22}O, the ^{22}Si 2_{1}^{+} excitation energy indicates the existence of a weakened Z=14 subshell closure. To reproduce the new spectroscopic information and known ^{22}Al levels, the energy of the 1s_{1/2} orbit must be substantially decreased, which imparts Thomas-Ehrman shifts to all excited states observed in the present Letter and explains the structure of nuclei in the sd shell for this region of the proton drip line.