Measurement and modeling of hydrogen vibrational and rotational temperatures in weakly-ionized hydrogen discharges

Neutral hydrogen molecule vibrational and rotational temperatures are measured using visible spectroscopy in two weakly-ionized, steady-state laboratory plasmas: a dc reflex-arc discharge and a rf etcher plasma. The rotational temperature in these experiments is found to be of order 5× less than the vibrational temperature, indicating that rotational internal energy should not be neglected if accurate neutral modeling of these plasmas is desired. A 0-D, steady-state model is developed which predicts measured ro-vibrational level populations within a factor of 10 or better and the overall vibrational and rotational temperatures within a factor of 2. In the plasma conditions studied here (electron density 108 < ne < 1013 cm−3, electron temperature 2 < Te < 10 eV), direct electron-impact excitation appears to be the dominant ro-vibrational heating mechanism, while wall collisions provide the dominant cooling mechanism.