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First‐order spatial dispersion effects in the Raman spectrum of NaClO 3
Author(s) -
Ouillon R.,
Pinan Lucarre J. P.,
Ranson P.
Publication year - 1994
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250250709
Subject(s) - raman spectroscopy , monochromator , degenerate energy levels , optics , raman scattering , molecular physics , dispersion (optics) , wave vector , physics , chemistry , wavelength , quantum mechanics
In cubic crystals the infrared‐active triply degenerate modes split into an LO and a doubly degenerate TO mode. For crystals with T symmetry, first‐order spatial dispersion splits the polar TO modes into a set of two circularly polarized T + and T − modes whose frequencies have only a small separation. Using incoherent high‐resolution Raman spectroscopy (a tandem Fabry–Perot Raman double monochromator of limiting resolution 0.005 cm −1 ), we have measured the splitting of the low‐energy TO lattice modes in the optically active material sodium chlorate. Experiments were performed in various scattering geometries to separate the optical Raman‐active modes of different symmetries ( A, E, LO and TO modes). Furthermore, the difference in the Raman response of the T + and T − modes to left or right circularly polarized incident light was detected and analysed. We measured for the three low‐energy TO modes (77, 98 and 125 cm −1 at T = 6 K) a splitting of 0.08, 0.08 and 0.105 cm −1 respectively in a right angle geometry and 0.11, 0.11 and 0.135 cm −1 respectively in a backscattering geometry (an increase in agreement with a shift proportional to the wave vector length).