This thesis can be divided into two parts.The aim of the studies described in the first part of the thesis isto make clear the dominating processes in the selective decorrpositionof certain solutes that follow low-terrperature radiolysis of crystalline hydrocarbons. 1. The isotope effect in the production of radicals has been studiedby Electron Spin Resonance and Gas Chromatography/MassSpectrometry in the C10H22/C10D22 system. Two independent methodshave never been used on the same system in this contextbefore. The methods gave the same ratio of protiated to deuteratedradicals. 2. The isotope effect in the production of hydrogen gas has beenstudied with Mass Spectrometry in the C10H22/C10D22 system. 3. The amount of reactive D-atoms has been measured in C10D22 using an olefin, C10H20, as a scavanger. 4. The effect of an electron scavenger, C8H16Cl2, in C10H22 has been investigated. Two processes for the explanation of the isotope effects are discussed. a. transfer of excitation energy b. selective abstraction. The results show that reactive D-atoms are present in the C10D22 system and suggest that the isotope effects can be explained by selectiveabstraction. The effect of the electron scavenger can beexplained by energy transfer, but not entirely by selective abstraction. In the second part of the thesis, a method to simulate Electron SpinResonance spectra for the case of a Hamiltonian containing nuclearinteractions is described. The method has been applied to the S = 1 case. It is suggested that the method can be generalized to an arbitraryelectronic spin state, and to include second order nuclear corrections. / digitalisering@umu

This thesis reports the use of both dc and ac electric fi eld induced resonant energy transfer, RET, between cold Rydberg atoms as a useful tool for enhancement of interatomic interactions. A general technique for laser frequency stabilization and its suitability for Rydberg atom excitation is also demonstrated. RET between cold Rydberg atoms was used to determine Rydberg atom energy levels. The ⁸⁵Rb atoms are laser cooled and trapped in a magneto-optical trap. For energy level determination experiment, atoms were optically excited to 32d₅/₂ Rydberg states. The two-atom process 32d₅/₂ + 32d₅/₂ → 34p₃/₂+30g is resonant at an electric fi eld of approximately 0.3 V/cm through dipole dipole interaction. The experimentally observed resonant fi eld, together with the Stark map calculation is used to make a determination of the ⁸⁵Rb ng-series quantum defect to be ⵒg(n = 30) = 0.00405(6). The ac Stark eff ect was also used to induce RET between cold Rydberg atoms. When a 28.5 GHz dressing field was set at speci fic fi eld strengths, the two-atom dipole-dipole process 43d₅/₂ + 43d₅/₂ → 45p₃/₂ + 41f was dramatically enhanced, due to induced degeneracy of the initial and final states. This method for enhancing interactions is complementary to dc electric- field-induced RET, but has more flexibility due to the possibility of varying the applied frequency. At a dressing field of 28.5 GHz all of the participating levels (43d₅/₂, 45p₃/₂ and 41f) show signi cant shifts and these give a complicated series of resonances. An oscillating electric fi eld at 1.356 GHz was also used to promote the above RET process where the atoms are initially excited to the 43d₅/₂ Rydberg states. The ac fi eld strength was scanned to collect RET spectra. Di fferent resonances were observed for diff erent magnetic sublevels involved in the process. Compared to the higher dressing field frequency of 28.5 GHz, the choice of dressing frequency of 1.356 GHz, which is slightly blue detuned from the 41f - 41g transition, and structure of the spectra may be understood, by analogy with the dc field case.

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Chemistry and Chemical Biology." Includes bibliographical references (p. 133-142).

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 86-103).

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 71-79).

Thesis (Ph. D.) in Physics--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 96-102).

Morphology is the origin of life and function. Defining and designing morphology, understanding the relationship between morphology and function, is an essential theme in a number of research areas. In conjugated polymer research, the major obstacles to achieving these goals are the heterogeneity and complexity of conjugated polymer films. In the study presented in this dissertation, various single molecule spectroscopy techniques were used as an approach to minimize the complexity of these problems. By using excitation polarization spectroscopy, it was discovered that single chains of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) assume a highly ordered rod conformation despite the fact that the morphology of bulk films is known to be amorphous. The comparison of results from experiments and a coarse grained bead-on-a-chain simulation suggested that single chains have the ability to use a thermally induced defect to maximize [pi]-[pi] stacking and adopt a rod conformation as a stable conformation. Bias-induced centroid spectroscopy (BIC) on highly ordered single chains demonstrated that the energy transfer scale could be an order of magnitude larger than the value typically measured for bulk films. It was further demonstrated that such an extraordinary long energy transfer was not a unique property of single chains but was also observed in aggregates as long as the morphology was ordered. These studies were extended to another model compound poly(3-hexylthiophene) (P3HT) to generalize the mechanism of morphology formation and the structure-property relationship. For P3HT, it was shown that side-chains were a very important factor in determining single chain conformation, while the conformation of MEH-PPV was not affected by side-chains. By controlling the side-chains, both ordered and disordered P3HT chains were obtained. The comparison of results from experiments and an energy transfer model simulation quantified that energy transfer was at least twice as efficient in ordered chains as in disordered chains. In aggregates, the difference between the energy transfer efficiency of ordered and disordered morphology was even larger than that in the case of single chains. These results could suggest that there is a very fast energy transfer mechanism that occurs through interchain interactions when chains are packed in ordered fashion. / text

published_or_final_version / Physics / Master / Master of Philosophy

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