Document Type

Dissertation

Date of Award

1977

Keywords

Infrared spectroscopy, Alkali metal halides, Spectra

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Robert L. Pompi

Second Advisor

Tsu-Ming Wu

Third Advisor

Newton Greenberg

Abstract

The near infrared absorption spectrum of SH^- in KCl, KBr, KI, RbCl, RbBr, and Rbl has been measured over a range of temperatures extending from room temperature down to l.l degrees K. The dependence of the absorption spectra on an externally applied electric field was also measured at liquid helium temperatures.

The zero field spectra in all cases exhibited several closely spaced absorption lines about 1.0 cm'1 apart which showed no temperature dependence in the range of 1.1 to 20 degrees K. The absence of a temperature dependence rules these lines out as tunneling levels and indicates the tunnel splitting is small compared to 1.0 cm^-1. An upper limit on the tunnel splitting of 0.3 cm^-1 can be inferred from the half—width of the main band. In all systems except KCl:SH^- I vibrational side bands were found at about 100 cm^-1 from the main vibrational band. These bands exhibited a strong temperature dependence, the sum band sharpening and the difference band disappearing at helium temperatures.

It has been found that the Devonshire Model does not agree with the measured spectra. Somewhat better agreement is found with localized oscillator models, but it is impossible to decide unambiguously between , , or potential minima directions because the individual tunnel levels cannot be resolved.

With an external electric field applied parallel to the polarized IR beam, both shifts in main—peak frequency and intensity were observed but both effects were very small indicating either a small dipole moment for SH- or high crystalline barriers to rotation. The dichroism, or change in peak absorption coefficient, was found to be proportional to E^2/T and in all cases except one the absorption was found to increase with an increase in E. The dichroic results were found to be inconsistent with simple classical models which use Boltzmann statistics to predict the numbers of molecules lying along potential minnna directions. Better agreement between experiment and theory was found when the dichroic results were described by a localized oscillator model with the external electric field treated as a perturbation.

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