In the general outline of variables in spectrochemistry (§ 1. 1) we considered briefly the main features of sample excitation. When the vaporizing sample is released from the electrode, fractions of its constituents enter into the discharge zone, where they dissociate, ionize, and become excited. Most of the elements are present in the plasma partly as neutral atoms, partly as singly-charged ions; only a few form molecules or radicals that are stable at the high temperatures prevailing in the core of the arc (cf. § 11.3). The plasma of the free-burning arc, consisting mainly of the elements of the surrounding atmosphere (see § 7.9), flows continuously upwards by convection (see § 2.3). The sample vapours enter into the upward-flowing gas and are transported by diffusion, by migration under the influence of the axial electric field (§ 3.1 and 3.2), and by the gas flow.
KeywordsRadial Distribution Absolute Concentration Radial Diffusion Convection Velocity Discharge Zone
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