interference terms to the polarization at 90° was found in this way to be ^ 0.3%, If only El and Ml amplitudes need be considered then the differential photoneutron polarization [the differential cross section o(9) x the polarization p(0)] can be written aswhere A EM depends on £1-M1 interference and B BBtMM depends on the products of El and Ml amplitudes that lead to different final states of the np system. Of course, only A EM contributes to the polarization at 90°. The primary effect of the MEC is to increase 4 the Ml transition amplitudes, namely the ( 3 S X + 3 D 1 ) -1 S 0 transition. Thus, the magnitude of the photoneutron polarization ^(90°) must become larger. In order to explain the present data, one must reduce the Ml transition amplitude in such a manner that the thermal n-p capture cross section is not changed, or increase the El transition amplitude in a way that does not alter the total photoabsorption cross section. 13 Clearly, a high-accuracy angular distribution of photoneutron polarization and cross section is necessary in order to unravel the multipole components of the reaction 2 H(y,n)H at low energy. In addition, further theoretical work will be necessary in order to explain this simplest nuclear reaction. We wish to thank B. Day, F. Coester, and PACS numbers: 31.20.WbThe behavior of a highly excited atom in a strong magnetic field is a topic of much current interest. 1 The present studies were motivated E. Hadjimichael for illuminating discussions.Classical trajectories and semiclassical eigenvalues are calculated for an atomic Rydberg state in a magnetic field. Perturbation theory describes a classical trajectory as a Kepler ellipse which rocks, tilts, and flips in space as orbital parameters evolve slowly in time. Exact numerical calculations verify the accuracy of perturbation theory for w^30, B^6T. Action variables are calculated from perturbation theory and from exact trajectories, and semiclassical eigenvalues obtained by quantization of the action. Good agreement is found with observations.