Mechanism of atom excitation in carbon furnace atomic-emission spectrometry

Abstract

By consideration of electronic and vibrational excitation temperatures and the ionisation temperature, it is demonstrated that local thermal equilibrium (LTE) is established under the practical analytical conditions of interrupted gas flow in which commercial carbon furnace atomisers are used as emission sources. The electron concentration is shown to be derived from thermionic emission from the carbon tube and calculated values of 5.2 × 10¹⁰ cm^–3 at 2558 K and 1.3 × 10¹¹ cm^–3 at 2766 K are reported. The processes that contribute to the establishment of LTE are considered in detail, and it is suggested that molecular collisions make the major contribution to atomic excitation under all conditions, but that radiation absorption may be significant when a monatomic gas is used as purge gas and when molecules are present as impurities at concentrations of only 0.01%.