Measurement of an unusualM1transition in the ground state of Ti-likeW52+

Abstract
Using a high-efficiency, transmission grating spectrometer the 3s23p63d4 J=23 ground-state transition was measured in Ti-like W52+. The measurement has achieved 20 times better precision than the only previously reported high-Z measurement. As such, it tests recent structure calculations for complex highly charged ions. Discrepancies of around 100Å are found. This is true even for semi-empirical calculations. The measurement, however, validates a very recent calculation with which agreement is within 2Å.