Raman measurements on the hydroxyl ion in several alkali-halide crystals
Peascoe, Judith Gould
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https://hdl.handle.net/2142/29599
Description
Title
Raman measurements on the hydroxyl ion in several alkali-halide crystals
Author(s)
Peascoe, Judith Gould
Issue Date
1973
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
alkali-halide crystals
Raman scattering
Language
en
Abstract
"Raman measurements were made on several a1ka1i""""ha1ide crystals containing OH- impurity between 2 K and 300 K. An argon laser was used as the source of excitation. Filtration of the scattered light provided by -1 an iodine cell permitted direct observation of the spectra below 40 cm for the first time.
In NaCl:OH, a line was observed in the Eg spectrum at 3.2 cm-l. It represented the transition between the Alg and Eg levels in the ground-state multiplet of (100) wells 0 Additional lines were observed at 11.5 cm -1 and 14 cm -1 in the T2 spectrum and 14 cm-1 and 2-1 cm in the Eg spectrum.. The pure stretching transition was observed at 3651.6 cm -1. High frequency sidebands of the stretching band were observed up-'shifted -1 by 4.6, 7.5. and 12 cm. With the additional information given by the known infrared spectra of NaCl:OH-, the energy levels were assigned from
an empirical model based on that of Devonshire. The assignments explained a temperature=dependent peak down-shifted from the stretching peak by 4 cm-l.
For OH- in Kel, lines were observed in the T2g spectrum at 32, 303,-,1 and 378 em as well as lines shifted from the stretching band by 32, 298, and 352 cm -1 Similarly OR - in KBr has Hnes in the T2g spectrum at 36, -1 313, and 409 em as well as lines shifted from the stretching band at 31 cm- l and 311 cm- l The OH- in the alkali halides was assumed to undergo two types of torsional movement, one a motion about a fixed center of mass which results -1 in the 300 cm band and the other a motion of the entire ion dynamically -1 coupled to the lattice which explained the lines of less than 40 cm
To understand this case, one must assume that the center of mass is displaced
from the lattice siteQ The effective moments of inertia, computed for the low-frequency lines from the Devonshire model of approximately 14 amu-X2 NaC1:0H-, 13 amu-XZ for KC1:0H- and 16 amu-A2 for KBr:OH- are consistent with this center-of-mass assignment.
A model based on the localization of the OH- ion about a set of equilibrium directions was developed to explain the intensity of the spectra. With this model, the ratios of the intensities of the E and g the A1g components of the stretching band were used to determine the anisotropy of the po1arizabi1ity derivatives. As interpreted by the tight-well model, the presence of a 1ibrator -1 -1 in the Eg spectrum at 283 cm and one in the TZg spectrum at 370 cm confirmed the (110) orientation of OH- in KI. Attempts 'were made. to explain the. changes in linewidth of t.he A1g stretching spectrum of NaCl:0R- and the changes in line shape of the depolarized stretching spectra of OR- in NaC1,KC1, and KBr in terms of the broadening of individual lines and of the changes in correlation times resulting to a large degree from the thermal occupation of excited
states."
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