Eur. Phys. J. D 46, 103-109 (2008)
https://doi.org/10.1140/epjd/e2007-00281-7

Diagnosis of negative hydrogen ions and rovibrational distribution of H₂ molecule in non-thermal plasmas

¹ Laboratory of Plasma Physical Chemistry, P.O. Box 288, Dalian University of Technology, 116024, Dalian, P.R. China
² State Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, 116024, Dalian, P.R. China

Corresponding author: ^a yongxu@dlut.edu.cn

Received: 14 February 2007
Revised: 7 July 2007
Published online: 5 October 2007

Abstract

Rovibrational excited hydrogen molecule plays an important role for the production of H^- ions. The correlation between H^- ion density and rovibrational distribution of H₂ molecules has been investigated in dielectric barrier discharge hydrogen plasmas via optical emission spectrometry and molecular beam mass spectrometry. The relative vibrational distribution of molecular hydrogen in the electronic ground state has been determined by the best fitting to the Fulcher-α band emission lines. It is shown that the ratio of the Q_(0-0)(1) to Q_(1-1)(1) line is very suitable and simple for the diagnosis of vibrational temperature in the range of 1500 to 7500 K. At certain discharge conditions (ac 40 kHz, 14 kV), the vibrational temperature decreases from 3600 to 2400 K as the pressure increases from 100 to 200 Pa and the negative ions density near the ground electrode also decreases as the pressure increases. Both the hydrogen ions density and the vibrational temperature increase with the increasing of discharge voltage. It is found that the evolution of negative atomic hydrogen ions density greatly depends on the vibrational temperature.