The donor transition energy in ZnSe is calculated as a function of the
magnetic-field strength. Through a variational approach, the wave fun
ctions are obtained, which are used in a calculation of the magnetopol
aron effect within second-order perturbation theory. Our theoretical a
nalysis finds good agreement with the experimental results for the is
1s --> 2p(+) transition up to the 150-T region if both the effects of
magnetopolarons and band nonparabolicity are included.