Polarized Raman scattering measurements have been made of a single crystal of L‐tyrosine by the use of a Raman microscope with the 488.0‐nm exciting beam from an argon ion laser. The L‐tyrosine crystal belongs to the space group P212121 (orthorhombic), and Raman scattering intensities corresponding to the aa, bb, cc, ab and ac components of the crystal Raman tensor have been determined for each prominent Raman band. A similar set of measurements has been made of L‐tyrosine‐d4, in which four hydrogen atoms on the benzene ring are replaced by deuterium atoms. The effects of NH3 → ND3 and OH → OD on the Raman spectrum have also been examined. In addition, depolarization ratios of some bands of L‐tyrosine in aqueous solutions of pH 13 and pH 1 were examined. For comparison with these experimental results, on the other hand, ab initio molecular orbital calculations have been made of the normal modes of vibration and their associated polarizability oscillations of the L‐tyrosine molecule. On the basis of these experimental data and by referring to the results of the calculations, discussions have been presented on the Raman tensors associated to some Raman bands, including those at 829 cm−1 (benzene ring breathing), 642 cm−1 (benzene ring deformation), and 432 cm−1 (Cα‐Cβ‐Cγ bending). © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 61–71, 1998

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