The Cavity Ring-down Spectroscopy Research Of OH And Singlet Delta Oxygen In Dielectric Barrier And Microwave Discharge Plasmas

In non-equilibrium low-temperature plasmas, energetic physico-chemical processes can be induced by active species at low ambient temperatures. Therefore, measurements of the active species are needed to study and improve plasma technology, also to explore physico-chemical processes. OH, as a very lively diatomic free radicals, plays an significant role in atmospheric chemistry, combustion chemistry and the field of plasma surface treatment; Singlet oxygen is one of the excited state of unstable oxygen molecules, it has very important impact on biological oxidation in the living body, light conversion process of air pollutants and metabolism of organism. However, determining their concentrations is a challenging problem in the atmosphere or in laboratory experiments because of their short lifetime and low concentration, so sensitive detection technology is needed. The advantage of cavity ring-down spectroscopy (CRDS) over normal absorption spectroscopy results from, firstly, the intrinsic insensitivity to light source intensity fluctuations and, secondly, the extremely long effective path lengths. The technique is especially powerful for concentration measurements of trace gas. The present work reports the determination of OH radical and singlet delta oxygen in dielectric barrier and microwave discharge plasmas via continuous wave cavity ring-down spectroscopy. The main contents have been summarized as followings:(1) In this work, microwave discharge and cavity ring-down spectroscopy were used to measure the P-branches of OH X2Πi(v'=2←v"=0) bands for its number density measurements, and the OH rotational temperature (TR) was measured by Boltzmann plots. The influence of pressure, microwave power, the addition of O2 and N2 on number density and rotational temperature of OH radicals has been investigated. The low detection sensitivity and minimum number density of the apparatus have also been obtained.(2) Through the measurement of O2 (b1Σg+-a1Δg) band by cavity ring-down spectroscopy in different experimental conditions (frequency, microwave power, discharge gas, pressure and voltage), singlet delta oxygen (SDO) has been investigated in dielectric barrier and microwave discharge plasmas, its number density was caculated in microwave discharge plasma finally.