Observation of 2p3 d (1Po)? 1s3d (1De) Radiative Transition in He-like Si, S, and Cl Ions, Kasthurirangan, S., Saha J. K., Agnihotri A. N., Bhattacharyya S., Misra D., Kumar A., Mukherjee P. K., Santos J. P., Costa A. M., Indelicato P., et al. , Volume 111, p.243201, (2013)