A tutorial discussion on measurements of rotational temperature in inductively coupled plasmas

Abstract

The intensities in the rotational fine structure of electronic bands such as B 2Σ + u → X 2Σ + g of N + 2, A 2Σ + → X 2Π i, of OH and B 3Σ u − → X 3Σ − g of O 2 are often used for measurements of rotational temperature prevailing in plasma sources such as the inductively coupled plasmas (ICP) and microwave induced plasmas (MIP). Certain misconceptions (such as the incorrect use of Hund's rule, the use of transition probability in conjuction with the equation for line strength, and the incorrect assignment of rotational lines) in the calculations of rotational temperatures have led to erroneous results. The main point of this paper is to emphasize that the interpretation of the rotational intensity distribution depends on both the angular momentum coupling and on the resolution of the instrument used. In this report, the introductory theory of rotational temperature measurement is reviewed and examples of correct and incorrect calculations are cited for ICP and MIP discharges sustained in argon, helium, argon-nitrogen, argon-oxygen and argon-air.