Analysis of unresolved thermometric groups of rotational lines of the OH UV spectrum in the wavelength range 310-378 NM

Abstract

Previous experimental and theoretical studies [1, 2, 3] of the UV spectrum of the OH radical (band head at 306.357 nm, transition Α2Σ,v=0→Χ2Π,v′=0), easily observed in hot gases containing oxygen and hydrogen (flames, plasma chemistry), have showed the existence of three groups of unresolved rotational lines which evolution against the rotational temperature is sensitive and monotonous. From a numerical simulation of the UV OH spectrum obtained with the experimental data of Diecke et Crosswhite [4], the variations of the amplitude of these unresolved groups of lines were calibrated as a function of the temperature and of the optical apparatus function. Since the 3 groups of unresolved rotational lines may be perturbed by atomic lines coming from electrode materials in plasma processes (it is the case for neutral aluminium lines at the wavelength 308.2 nm and 309.2 nm), the previous studies have been extended to other groups of unresolved lines in the wavelength range 310−318 nm. Experiments using an oxyacetylene flame clearly demonstrate that the new groups of unresolved lines give a too high rotational temperature value. This effect can be explained with an analysis of the different rotational components that constitute these unresolved groups of lines.