The first part of this thesis describes nonlinear dielectric relaxation experiments performed on various molecular glass forming-liquids, with an emphasis on the response at high frequencies (excess wing). A significant nonlinear dielectric effect (NDE) was found to persist in these modes, and the magnitude of this NDE traces the temperature dependence of the activation energy. A time resolved measurement technique monitoring the dielectric loss revealed that for the steady state NDE to develop it would take a very large number of high amplitude alternating current (ac) field cycles. High frequency modes were found to be ‘slaved’ to the average structural relaxation time, contrary to the standard picture of heterogeneity. Nonlinear measurements were also performed on the Johari-Goldstein β-relaxation process. High ac fields were found to modify the amplitudes of these secondary modes. The nonlinear features of this secondary process are reminiscent of those found for the excess wing regime, suggesting that these two contributions to dynamics have common origins.
The second part of this thesis describes the nonlinear effects observed from the application of high direct current (dc) bias fields superposed with a small amplitude sinusoidal ac field. For several molecular glass formers, the application of a dc field was found to slow down the system via reduction in configurational entropy (Adam-Gibbs relation). Time resolved measurements indicated that the rise of the non-linear effect is slower than its decay, as observed in the electro-optical Kerr effect. A model was discussed which quantitatively captures the observed magnitudes and time dependencies of the NDE. Asymmetry in these rise and decay times was demonstrated as a consequence of the quadratic field dependence of the entropy change. It was demonstrated that the high bias field modifies the polarization response to the field, even including the zero field limit.
This paper outlines the design and testing of a z-scan spectrometer capable of measuring the third order refraction index of liquids. The spectrometer underwent multiple redesigns, with each explored in this paper with their benefits and drawbacks discussed. The first design was capable of measuring the third order refraction index for glass, and found a value of 8.43 +- 0.392 x 10^(-16) cm^2/W for the glass sample, with the literature stating glass has a refraction index between 1-100 x 10^(-16) cm^2/W. The second design was capable of measuring the third order refraction index of liquids, and found values of 1.23 $\pm$ 0.121 $\e{-16}$ and 9.43 +- 1.00 x 10^(-17) cm^2/W for water and ethanol respectively, with literature values of 2.7 x 10^(-16) and 5.0 x 10^(-17) cm^2/W respectively. The third design gave inconclusive results due to extreme variability in testing, and and the fourth design outlined has not been tested yet due to time constraints.
Singly deuterated silylene has been detected and characterized in the gas-phase using high-resolution, two-dimensional, optical spectroscopy. Rotationally resolved lines in the 0[0 over 0][˜ over X]1A′ → [˜ over A]1A′′000X˜1A′→A˜1A″ band are assigned to both c-type perpendicular transition and additional parallel, axis-switching induced bands. The extracted rotational constants were combined with those for SiH2 and SiD2 to determine an improved equilibrium bond length, rSiH, and bond angle, θ, of 1.5137 ± 0.0003 Å and 92.04° ± 0.05°, and 1.4853 ± 0.0005 Å and 122.48° ± 0.08° for the [˜ over X]1A′(0, 0, 0) and [˜ over A]1A″(0, 0, 0) state respectively. The dispersed fluorescence consists of a long progression in the [˜ over A]1A″(0,0,0) → [˜ over X]1A′(0, ν2, 0) emission which was analyzed to produce vibrational parameters. A strong quantum level dependence of the rotationally resolved radiative decay curves is analyzed.