Evidence of catalytic production of hot atomic hydrogen in RF generated hydrogen/helium plasmas

Abstract

A study of the line shapes of hydrogen Balmer series lines in RF generated low pressure H 2 /He plasmas produced results suggesting a catalytic process between helium and hydrogen species results in the generation of 'hot' (ca. 28 eV) atomic hydrogen.Even far from the electrodes 'hot' atomic hydrogen was predominant in H 2 /He plasmas.Line shapes, relative line areas of cold and hot atomic hydrogen (hot/cold>2.5), were very similar for areas between the electrodes and far from the electrodes for these plasmas. In contrast, in H 2 /Xe only 'warm' (<5 eV) hydrogen (warm/cold<1.0) was found between the electrodes, and only cold hydrogen away from the electrodes. Earlier postulates that preferential hydrogen line broadening in plasmas results from the acceleration of ionic hydrogen in the vicinity of electrodes, and the special charge exchange characteristics of Ar/H 2 + are clearly belied by the present results that show atomic hydrogen line shape are similar for H 2 /He plasmas throughout the relatively large cylindrical (14 cm ID x 36 cm length) cavity.

Experimental study of the evolution of H α line profile in a pulse hydrogen discharge

“…Profiles of hydrogen spectral lines at low pressure have been the subject of experimental and theoretical research for many years [1][2][3][4][5][6][7]. In various types of discharges (radio frequency (RF) [2,8], direct current (DC) [9], dielectric-barrier discharge [10], hollow cathode glow discharge [11][12][13] and others) their profiles often exhibit anomalous broadening in pure hydrogen [1-3, 5-9, 13, 14] and in mixtures with hydrogen [10,[13][14][15][16]. The line profiles reflect the velocity distribution and the relative densities of the emitting particles.…”

“…The H α profile, for example, consists of several components, each one of them appearing due to different excitation processes [1][2][3][4][5][6][7][8][10][11][12][13][14][15][16]. The central, narrowest component reflects the velocity distribution of the thermal excited * Author to whom any correspondence should be addressed.…”

Spectroscopic investigation of wave driven microwave plasmas

“…Anomalous, even extreme, hydrogen line broadening was found in a number of mixed discharge plasmas excited via direct current ͑dc͒ or radio frequency ͑rf͒ electric fields. [1][2][3][4][5] The Balmer line spectra emitted by these discharges have typical multimode behavior, with widely broadened "wings" ͑"fast" hydrogen͒ and a sharp top ͑"slow" hydrogen͒. The results have usually been explained in terms of Doppler shift and broadening due to the acceleration of charges ͑such as H + , H 2 + , and H 3 + ions͒ in the high dc electric fields present in the sheath regions of these discharges.…”