Near infrared absorption bands of the hydroxyl ion in alkali halide crystals
Wedding, Brent Merle
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https://hdl.handle.net/2142/25702
Description
Title
Near infrared absorption bands of the hydroxyl ion in alkali halide crystals
Author(s)
Wedding, Brent Merle
Issue Date
1967
Doctoral Committee Chair(s)
Klein, Miles V.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
near infrared absorption
hydroxyl ion
alkali halide crystals
Language
en
Abstract
The near infrared absorption bands due to OH- in NaC1, NaBr,
KCI, KBr, KI, and RbC1 have been measured at temperatures ranging from
1.4~ to 380 oK. Energy levels of the hydroxyl dipole in the crystal
lattice were determined from the spectra.
The crystals were grown by the Czochra1ski m~thod in a purified
argon atmosphere. The spectra were measured with a spectrophotometer
assembled from connnercially available components. Three cryostats
were used: 1) an innnersion cryostat which operated at 1.4°K
with the sample in pumped liquid helium, 2) a conduction cryostat
with exchange gas switch coupling to the liquid helium bath for sample
temperatures between 4.SoK and 78°K, and 3) an exchange gas switch
equipped liquid nitrogen cryostat for temperatures between 78°K and
380 oK.
The helium temperature spectra consist of three classes of
absorption bands: 1) the O-H stretching absorption (main band) near
3600 cm-1, 2) a side band at about 300 cm-1 higher energy due to
torsional oscillation (libration), and 3) low-lying side bands at
splittings ranging from about 4 cm-1 in KI:OH to 40 cm- l in KBr:OH.
Spectra of KC1:0D and KBr:OD were measured to confirm the 1ibrationa1
assignment of the 300 cm- l band, and the rotational barrier was
calculated using the Devonshire theory.
The low-lying energy levels are not prediced by the Devonshire
theory, and are strongly dependent on the host lattice. RbC1:0H, KC1:0H,
and KBr:OH had side bands which peaked at 30, 32, and 40 cm-1 respectively,
and these had similar features. KI:OH had bands at 3.7 and 7.5 cm-1 at
4.S0K; the one at lower energy was frozen out at 1.4°K. NaC1:0H had
several bands between 3640 and 3670 cm -1, and some of these were strongly
temperature and concentration dependent. At 1.4°K there was a summation
side band at 11 cm-1 splitting, and at 4.S oK an additional summation band
split by S cm-1 was present. Two difference bands split by Sand 11 cm-1
were evident in the SOK spectrum.
The KC1:0H 32 cm-1 band shifted to 23 cm-1 with isotopic
substitution, giving an energy ratio of 1.4. The shift ratio for KBr
was much smaller, probably less than 1.1. The electric field induced
dichroism was measured at 1.4°K for the three alkali chlorides. With
parallel polarization, the 11 cm-1 band in NaC1:0H was enhanced, the
30 cm-1 band in RbC1:0H shifted to higher energy, and the 32 cm-1 band in
KC1:0H was quenched.
The half widths of the main band and 1ibrationa1 side band
were measured at various temperatures to observe the thermal broadening
of these excitations. Possible decay mechanism were proposed, but a
good theoretical fit to all the data over the entire temperature range
was not found.
The oscillator strength of the main band at liquid helium
temperature was about 10-3. Rotation-like motion of the dipole was
not observed at any temperature.
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