Doppler broadening of atomic-hydrogen lines in low E-field plasmas

Substantial broadening of the H$_{\alpha}$ lines of hydrogen admixed with preionized atoms is observed in filament heated and inductively coupled plasmas where the applied electric field is quite low. These filament heated hydrogen plasmas forms at low temperatures (e.g.) and low field strength ($\sim $1-2 V/cm) when argon and strontium were present with atomic hydrogen, exhibit H$_{\alpha}$ line broadening ($\sim $24 eV). H$_{\alpha }$ line broadening (20-24 eV) is also observed in inductively coupled plasma where the voltage drop across the plasma sheath is small. Moreover, the selective transfer of energy to H atom and the absence of comparable hot helium atoms ($<$0.5 eV) where the atomic mass ratio is 4:1 along with the absence of hot H atoms in Xe/H$_{2}$ plasmas are also inconsistent with the field acceleration model [e.g., Cvetanovic et. al. J. App. Phys., 97, 033302-1, 2005]. Plasma diagnostics include high-resolution optical emission spectroscopy, Langmuir probe and millimeter wave interferometeric measurements. The model of an energetic chemical reaction of hydrogen [Mills et. al \textit{IEEE Trans. Plasma Sci., }31, 338, 2003] as the source of broadening can explain the observation that certain plasmas exhibit the selective extraordinary broadening.