Anisotropic Zeeman Effect in Erbium Ethylsulfate When the Magnetic Field is Perpendicular to the C Uniaxis of the Crystal

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Abstract
When single crystals of erbium ethylsulfate, possessing C26h symmetry, were placed in a magnetic field with the direction of the field, the direction of the incident light, and the crystalline c axis mutually perpendicular, the energy and intensity of certain of the absorption lines were found to exhibit a dependence on the angle φm between the direction of the magnetic field and a newly‐defined crystalline x axis. Both the energy and intensity were periodic under 60° rotation about the c axis, but the maximum or minimum energy of every line occurred at φm=0°+n60°, while the maximum or minimum intensities of all the lines did not occur at a common angle. The energies of the levels, and their rotation coefficients and Zeeman splittings were determined for the ground term and for the line group at 27 500 cm−1. The spectral data were used in the measurement of the angle φ̄ between the usual crystallographic a axis and the x axis. This angle is a new observable which is a consequence of the C3h point symmetry at the rare‐earth ion site and which is characteristic of the crystalline environment. The experimental findings are in qualitative agreement with the theoretical work of Murao, Spedding, and Good, and with the results of our extended calculations.