Measurement of the concetration of the OH radical in an atmospheric pressure plasma pencil by laser-induced fluorescence
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| Year of publication | 2013 |
| Type | Conference abstract |
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| Citation | |
| Description | The concentration of radicals in reactive plasmas is an important parameter. The hydroxyl (OH) radical is known to be a strongly oxidizing species as well as an efficient source of UV radiation. Measuring the concentration of diatomic radicals at atmospheric pressure is a non-trivial task, especially in plasmas of small volume, such as the plasma pencil. One of the few methods suitable for this task is the laser-induced fluorescence, however, the interpretation of results at high pressures is difficult. We present a scheme suitable for measuring the concentration of the OH concentration in the flow of a rare gas mixing weakly with the ambient atmosphere. By exciting the ground vibrational state (v'=0) of the first excited electronic state (A2Sigma) we avoid the vibrational energy transfer (VET) in the laser-excited state. Together with the verified fact that the rotational energy transfer (RET) in the excited vibronic state is very fast, this justified using the very simple two-level model with (A2Sigma, v'=0) and (X2Pi,v''=0) vibronic states assumed to be in thermal rotational equilibrium during the whole process. The electronic quenching is taken into account by directly measuring the lifetime of the laser-excited state. The calibration is done by the Rayleigh scattering on air. |
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