The study of reactions of free radicals by time-resolved infrared semiconductor laser spectroscopy

点击翻译按钮获取中文摘要

The aim of this project is to investigate chemical reactions of free radicals generated by ultra-violet laser photolysis by applying highly sensitive time-resolved infrared semiconductor laser spectroscopy. Precursor molecules flowing through an absorption cell of about 2 m length are photolyzed by excimer laser pulses, and generated free radicals are monitored by an infrared semiconductor laser beam, which multipasses a White-type optics. The output of an infrared detector is A/D converted and sent to a personal computer, which performs dual-gated integration and time-profile accumulation.This apparatus was used to observe vibration-rotation spectra in the 5mum region of the FeCO and Fe(CO)_2 radicals generated by ArF excimer laser photolysis of Fe(CO)_5. For FeCo, detailed spectral assignment was accomplished, resulting in precise spectroscopic constants. Absorption lines of Fe(CO)_2 were also identified.These data were utilized for the measurement of decay curves of the FeCO and Fe(CO)_2 radicals, from which rate constants (in units of cm^3 molec^<-1> sec^<-1>) were derived as 1.25(5)*10^<-10> and 1.76(10)*10^<-10> for reactions of the respective radicals with the precursor Fe(CO)_5. Measurement was also made for systems with mixed gases, CO,CS_2, and (CN)_2, and reaction rates with these reactants were determined. The rate of the reaction with CO is 1.48(5)*10^<-11> for FeCo and 1.77(21)*10^<-11> for Fe(CO)_2. The radicals react with CO at an order of magnitude slower rate than with the precursor. The reaction rate with CS_2 is 2.87(24)*10^<-10> for FeCO and 1.69(15)*10^<-10> for Fe(CO)_2. FeCO reacts with (CN)_2 at a rate of 2.19(22)*10^<-10> and Fe(CO)_2 at 1.96(17)*10^<-10>. These reaction rates are comparable with those with the precursor.