Abstract
This article discusses laser-induced laboratory-air plasma measurements and analysis of hydroxyl (OH) ultraviolet spectra. The computations of the OH spectra utilize line strength data that were developed previously and that are now communicated for the first time. The line strengths have been utilized extensively in interpretation of recorded molecular emission spectra and have been well-tested in laser-induced fluorescence applications for the purpose of temperature inferences from recorded data. Moreover, new experiments with Q-switched laser pulses illustrate occurrence of molecular recombination spectra for time delays of the order of several dozen of microseconds after plasma initiation. The OH signals occur due to the natural humidity in laboratory air. Centrifugal stretching of the Franck-Condon factors and r-centroids are included in the process of determining the line strengths that are communicated as a Supplementary File. Laser spectroscopy applications of detailed OH computations include laser-induced plasma and combustion analyses, to name but two applications. This work also includes literature references that address various diagnosis applications.
Highlights
Practical applications of molecular spectroscopy include diagnosis of hydroxyl (OH) diatomic molecules in the study of laboratory plasma and chemical processes
This work aims to (a) publish OH line strength data [9] that can be directly utilized with associated graphing and non-linear fitting programs [10] that include the Nelder-Mead temperature (NMT) program and the Boltzmann equilibrium spectroscopy program (BESP); (b) communicate new experimental investigations for the purpose of estimating both typical signal strength and time-delays for occurrence of hydroxyl spectra in laboratory laser-sparks; (c) summarize possible approaches for determination of OH concentrations with reference to local equilibrium conditions for a variety of plasma species; (d) illustrate typical fluid physics phenomena that can be initially explored by employing shadowgraph techniques; (e) comment on the set extensively laser-induced fluorescence (LIF)- and optical emission spectroscopy (OES)- tested OH
Presence of the hydroxyl radical is usually associated with combustion, in laboratory air that contains residual moisture, OH emissions occur as a result of recombination radiation
Summary
Practical applications of molecular spectroscopy include diagnosis of hydroxyl (OH) diatomic molecules in the study of laboratory plasma and chemical processes. This work communicates state-of-the-art OH line-strength data that were well-tested in laser-induced fluorescence and emission spectroscopy diagnoses. Diagnosis usually utilizes methods that are frequently encountered in characterization of plasma [4]. This work communicates aspects of laser spectroscopy of OH that include active interrogation with excitation from ground- or lower molecular states and levels, viz. Laser-induced fluorescence (LIF), and passive analyses of excited molecular states or levels encoded in the emitted light from laser-induced plasma, viz. Laser spectroscopy examples primarily focus on OES of the OH molecule and at standard ambient temperature and pressure (SATP) laboratory conditions
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