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We have carried out model calculations of the photoionized intergalacticmedium (IGM) to determine the effects on the predicted ionic column densitiesdue to uncertainties in the published dielectronic recombination (DR) ratecoefficients. Based on our previous experimental work and a comparison ofpublished theoretical DR rates, we estimate there is in general a factor of 2uncertainty in existing DR rates used for modeling the IGM. We demonstrate thatthis uncertainty results in factors of ~1.9 uncertainty in the predicted N Vand Si IV column densities, ~1.6 for O VI, and ~1.7 for C IV. We show thatthese systematic uncertainties translate into a systematic uncertainty of up toa factor of ~3.1 in the Si/C abundance ratio inferred from observations. Theinferred IGM abundance ratio could thus be less than the solar Si/C ratio orgreater than 3 times the solar ratio. If the latter is true, then it suggeststhe metagalactic radiation field is not due purely to active galactic nuclei,but includes a significant stellar component. Lastly, column density ratios ofSi IV to C IV versus C II to C IV are often used to constrain the decrement inthe metagalactic radiation field at the He II absorption edge. We show that thevariation in the predicted Si IV to C IV ratio due to a factor of 2 uncertaintyin the DR rates is almost as large as that due to a factor of 10 change in thedecrement. Laboratory measurements of the relevant DR resonance strengths andenergies are the only unambiguous method to remove the effects of these atomicphysics uncertainties from models of the IGM.Comment: Submitted to ApJL. AASTex, 14 pages, 7 figure

Ionization Balance, Chemical Abundances, and the Metagalactic Radiation Field at High Redshift