Date of Award

Spring 2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

Lev N. Krasnoperov

Second Advisor

Joseph W. Bozzelli

Third Advisor

Carol A. Venanzi

Fourth Advisor

Zafar Iqbal

Fifth Advisor

Liang Chu

Sixth Advisor

Larry Lay

Abstract

The aim of the present study is to study the kinetics of elementary reactions of combustion importance at elevated temperatures and pressures. High pressure is encountered in many systems of practical importance such as internal combustion engines and rocket combustion chambers. Several reactions of OH, CH3 and HO2 radicals are studied. The pressure range covered in this study is 1 - 100 bar and the temperature range is 292 - 834 K. The experimental approach used is laser photolysis coupled to UV transient absorption spectroscopy. A unique high pressure heatable flow reactor is employed and a novel approach of direct introduction of liquid precursors using a high pressure syringe pump is developed in this study. Methyl radicals are produced by photolysis of acetone at 193.3 nm. Hydroxyl radicals are generated in the reaction of electronically excited oxygen atoms O(1D), produced in the photolysis of N2O at 193.3 nm with H2O. The reaction of O(1D) and hydroxyl with H2O2 produce hydroperoxy radicals. Temporal profiles of CH3 and HO2 are recorded via absorption at 216.4 and 224 nm, using xenon arc lamp and a spectrograph, OH radicals are monitored via transient absorption of light from a dc discharge H2O/Ar low pressure OH discharge lamp at ca. 308 nm. The absolute intensity of the photolysis light inside the reactor is determined by an accurate in situ actinometry based on the ozone formation in the presence of molecular oxygen. The reactions studied are OH + OH --> products (kOH+OH), CH3 + OH --> products (kCH3+OH), CH3 + CH3 --> products (kCH3 + CH3), and CH3 +HO2 --> products (kCH3+HO2). The pressure dependent rate constant in the self-reaction of OH radical is parameterized using the Troe expression as k1b,inf,OH+OH = (2.3 ± 0.5)x10-11(T/300)-0.5 cm3molecule-1s-1, k1b,0,OH+OH = [He] (1.4 ± 0.5)x10-30(T/300)-4.6±0.5 cm3molecule-1s-1, Fc = 0.37. The V- shaped temperature dependence of disproportionation channel (kOH+OH->H2O+O) based on combined current and previous studies in the temperature range of 233 - 2380 K is (5.1 exp(-T/190 K) + 0.30(T/300 K)1.73)x10-12 cm3molecule-1s-1. The rate constant of the reaction of CH3 and OH is determined as kCH3 +OH = (1.20 ± 0.20)x10-10(T/300)-0.49 cm3molecule-1s-1 pressure independent over the 1 - 100 bar range. The rate constant of self reaction of CH3+CH3 is kCH3+CH3 = 5.94x10-11 (T/300)-0.31cm3molecule-1s-1. The reaction of methyl radicals with hydroperoxy radicals (CH3+HO2 -> products), is studied at 295 K and 1 bar (He). The rate constant is (3.7 ± 1.8)x10-11 cm3molecule-1s-1 (295 K, 1 bar, He).

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