The evolution of the energy states of the phosphorous donor in silicon
with magnetic field has been the subject of previous experimental and theoretical
studies to fields of 10 T. We now present experimental optical absorption data to
18 T in combination with theoretical data to the same field. We observe features
that are not revealed in the earlier work, including additional interactions and anticrossings
between the different final states. For example, according to the theory, for
the “1s →2p+” transition, there are anti-crossings at about 5, 10, 14, 16, and 18 T.
In the experiments, we resolve at least the 5, 10, and 14 T anti-crossings, and our data
at 16 and 18 T are consistent with the calculations.