On The Apparent Narrowing of Radio Recombination Lines at High Principal
  Quantum Numbers
  We critically analyze the Bell et al. findings on "anomalous" widths of
high-order Hydrogen radio recombination lines in the Orion Nebula at 6 GHz. We
review their method of modified frequency switching and show that the way this
method is used for large \Delta n is not optimal and can lead to
misinterpretation of measured spectral line parameters. Using a model of the
Orion Nebula, conventional broadening theory and Monte Carlo simulation, we
determine a transition-zone n = 224, ..., 241 (\Delta n = 11, ..., 14), where
measurement errors grow quickly with n and become comparable with the
measurement values themselves. When system noise and spectrum channelization
are accounted for, our simulation predicts "processed" line narrowing in the
transition-zone similar to that reported by Bell et al. We find good agreement
between our simulation results and their findings, both in line temperatures
and widths. We conclude, therefore, that Bell et al.'s findings do not indicate
a need to revise Stark broadening theory.
