I. Calculation of Vibrational Transition Moments. II. Photochemistry of Vibrationally Excited Hydrogen Iodide. III. Photochemistry of Iodine Monochloride in Hydrogen

The text of this thesis is divided into three sections. In Part I, semi-empirical calculations of vibrational transition moments in general and hydrogen halide transition moments in particular are investigated. Semi-empirical transition moments, calculated using traditional approximations for the electric dipole operator, M(R), are compared with the exact vibrational transition moments for two hypothetical molecules in paper 1. The comparisons indicate that applying boundary conditions to an approximate M(R) does not significantly improve the transition moments predicted by that M(R). In paper 2, the same hypothetical molecules are used to evaluate a new method of obtaining M(R) from spectroscopic data, using each rovibrational moment in the vibrational bands rather than just the band centers. This method allows one to obtain an additional term in the Taylor series expansion of M(R), which produces corresponding improvement in the predicted vibrational transition moments. This new method is used on the experimental results available for HI and HF in papers 3 and 4, respectively. Here the rovibrational transition moments are also used to verify and determine the signs of measured transition moments. The reaction and vibrational relaxation of hydrogen iodide are discussed in Part II of this thesis (paper 5). Thermal and photochemical decomposition studies performed on HI yield the following results: (1) A small first-order component in the dark (thermal) reaction was detected in addition to the well-known second-order component. (2) The activation energy of the second-order reaction component between 660 and 710 K is 52.9±2.8 kcal/mole as compared with the 44 kcal/mole previously reported. (3) While the rate of the HI decomposition was enhanced in the photochemical experiments, a kinetic analysis indicated that this enhancement was due to thermal heating rather than by the reaction of vibrationally excited HI. (4) Theoretical estimates of vibrational reaction and relaxation rates were made suggesting experimental conditions which could lead to observation of vibrational enhancement of this reaction. The photochemistry of iodine monochloride in hydrogen is the subject of Part III. In paper 6, the quantum yield of HC1 formation in mixtures of IC1 and H2 is remeasured. The results indicate that while earlier conclusions are qualitatively correct, the secondary reactions in the IC1-H2 system are more complicated than previously envisioned. The reaction ratio of IC1 to H2 with C1 at 298.05 K is 1133± 69. This implies that the reported rate constant for the reaction: C1+ IC1 → C12 + I, determined by the photolysis of pure IC1 is several orders of magnitude too small.