Collisional quenching of OH (A2Σ+) measured by time-resolved LIF spectroscopy

Abstract

Optical diagnostics, i.e. imaging and spectroscopic techniques, are widely employed in the diagnostic of plasmas and discharges. They allow to probe the system being studied in a noninvasive way with sub-nanosecond time resolution. They are of great interest because of their analytical use, allowing to probe transient species that are believed to play a role in the process. Laser induce fluorescence (LIF) is successfully utilized to selectively investigate single species by exciting electronic transitions. The accessible information is primarily represented by the relative concentration of the species being probed. This information is assessed by means of theoretical models that take into account vibrational (VET) and rotational (RET) energy transfer as channels for the population of excited energy states, as well as fluorescence quenching by other gaseous species which are part of the gas mixture. Knowledge of the relevant rate constants is necessary and there is a need of rate constant data, especially at elevated pressures. In this framework, we present an experimental work that is meant to obtain novel data on quenching rate of OH at high pressure (of the order of 100 Torr) of the He gas carrier. We adopted a one pass scheme in which the laser pulse, with time duration of the order of tens of nanosecond, both produces the ground state OH radical, via photodissociation of H2O2, as well as the A2Σ+ excited state by absorption. Quenching species are those of interest in high-pressure discharges developed for the CO2 reforming, such as CO2, CO, hydrogen and methane.