1. Could you explain the significance of your article to the non-specialist? (50-100 words)

According to the current standard model of the Universe, chemistry began with the formation of the first molecules, a few hundred thousand years after the Big Bang, when the matter and radiation had cooled to a temperature of approximately 4000 K and reached a state in which the hydrogen was approximately half in the form of free protons and half neutral atoms. Hydrogen molecules formed by the two-body association reaction of the H^- negative ion and the H atom, following the radiative attachment of electrons to H atoms to form the negative ion. I have computed the abundances of all the important forms of hydrogen, deuterium, and helium in the well constrained standard cosmological model. The space-time of the expanding Universe between the observer (here and now) and the so-called surface of last scattering (where the cosmic background radiation last interacted with matter) constitutes a kind of absorption cell with the cosmological background as a light source.

The new result is a prediction that the primordial hydrogen negative ions should produce a small, but measurable feature in the submillimetre-wave spectrum of the background radiation, which is otherwise a nearly perfect blackbody. A search for this feature will test directly our understanding of primordial chemistry.

2. What has motivated you to conduct this work?

There have been several motivations for this work. First, improvements in measurement techniques during the last decade have brought observational cosmology into the realm of the exact sciences. When I first investigated cosmological chemistry 20 years ago with a research student, William Latter, the subject was rather more speculative with many poorly constrained parameters.

Thus it was interesting to re-visit this problem now that the cosmological parameters are no longer the limiting uncertainties in the model. Second, my immediate motivation was to present something new and potentially measurable at a Faraday Discussion.

3. Where do you see this work developing in the future?

My former student and I will prepare a more detailed article for the astrophysical literature. The prediction of a spectroscopic feature in the cosmic background radiation could affect the design of a future satellite-borne spectrometer. 

4. Are there any particular challenges facing future research in this area? 

A general challenge is the rapid pace of research in measurements of fluctuations in the cosmic background radiation. A particular challenge in the case of my prediction is that the effect is small, although measurable with existing technology.