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Spectral line shapes and shifts of non-hydrogenic spectral lines of neutral atoms are considered for diagnostics of low electron density high pressure plasmas. Difficulties in application and limitations of this spectroscopic diagnostic technique are discussed in detail. The simultaneous presence of comparable Stark, Van der Waals and sometimes resonance broadening is discussed and a procedure to deduce the electron number density from the measured line width and/or shift is described. The importance and requirement of high accuracy theoretical and experimental data for plasma diagnostics are also discussed.

Excited neutrals and fast ions produced in a 13.56 MHz radio-frequency discharge in a 90% argon -10% hydrogen gas mixture were investigated, respectively, by spatially and temporally resolved optical emission spectroscopy, and by mass-resolved measurements of ion kinetic energy distributions at the grounded electrode. The electrical characteristics of the discharge were also measured and comparisons are made with results obtained for discharges in pure HZ under comparable conditions. Measurements of Balmer-alpha (H,) emission show Doppler-broadened emission that is due to the excitation of fast atomic hydrogen neutrals formed from ion neutralization processes in the discharge. Temporally and spatially resolved emission profiles of the H, radiation from the Ar-H, mixture are presented for the "slow" component produced predominately by electron-impact dissociative excitation of Hz, and for the "fast" component corresponding to energies much greater than can be derived from dissociative excitation. For the Ar-Hz mixture, the fast component is significantly enhanced relative to the slow component. The measured kinetic-energy distributions and fluxes of predominant ions in the At-H2 mixture, such as Hl, Hi, H", and At-H+, suggest mechanisms for the formation of fast hydrogen atoms. The interpretation of results indicate that Hf and/or Hl , neutralized and backscattered by collision with the powered electrode, are the likely sources of fast hydrogen atoms that produce Doppler-shifted H, emission in the discharge. There is also evidence at the highest pressures and voltages of "runaway" H+ ions formed near the powered electrode, and detected with kinetics energies exceeding 100 eV at the grounded electrode. I. lNTRODUCl-IONRadio-frequency (r-f) discharges produced in argonhydrogen mixtures are useful for surface cleaning applications,' while discharges involving mixtures of argon, hydrogen, and methane have been used for etching of GaAs wafers.2 An understanding of these processes requires a knowledge of the role of collisions of ions and energetic neutrals with surfaces and other particles in the plasma. Particularly, in colhsion dominated discharges, ion and neutraf transport in the sheath region are important in determining the discharge-surface interactions.In addition to industrial applications, ion transport in Ar-Hz gas mixtures has been considered as a prototype system for experimental investigations and rigorous quantumtheoretical studies.3-10 A recent review article on stateselected and state-to-state cross-section measurements for several ion-molecule reaction systems shows that an increasing interest has been paid to the Ar-Hz system."Few investigations in At--H, mixtures have been performed in low pressure dc'2-'4 or rf" discharges. A recent optical emission study*' of an At-H2 mixture in 13.56 MHz rf glow discharges shows an increase in Doppler-broadened Balmer-alpha (H, , X=656.3 nm) emission when argon is "'Present address: Department of Chemical and NucIear Engineering, University of New Mexico, Albuque...

Experimental measurements of the center of the H_{beta} Stark profile on three different installations have been done to study its asymmetry in wide ranges of electron density, temperature, and plasma conditions. Theoretical calculations for the analysis of experimental results have been performed using the standard theory and computer simulations and included separately quadrupolar and quadratic Stark effects. Earlier experimental results and theoretical calculations of other authors have been reviewed as well. The experimental results are well reproduced by the calculations at high and moderate densities.

The spectral and spatial profiles of atomic hydrogen emission (the Balmer lines Hα and Hβ) from a low-pressure rf (13.56 MHz) discharge in H2+Ar mixtures have been studied. The plasma emission was observed in a direction normal to the applied electric field. The Hα profiles exhibit central narrow components and wide components which are due to Doppler broadening. Comparisons of the Hα profiles in a pure hydrogen plasma with those in H2+Ar mixtures show that collisions of molecular hydrogen ions and hydrogen atoms with argon atoms play a significant role in the production of the Hα profile shapes.