Is a detailed absorption spectrum available for carbon dioxide from 300-1100nm? I believe that carbon dioxide does not absorb light in the visible region, but is a spectrum available somewhere online that shows this as a fact? As in a straight horizontal line at 100% transmission?
I would be interested to see if there are any minimal areas of absorption anywhere at all. This spectrum must have been run and presumably discarded as worthless. It is not easy to find online amidst so much information concerning carbon dioxide's main absorption bands elsewhere.
Similar information for methane and water vapour would also be useful.
 A: Here are the absorption spectra of some atmospheric gases
for wavelengths from $0.1\ \mu$m to $100.0\ \mu$m.

(image from "Cold Facts on Global Warming" by T.J.Nelson)
Especially you can see, the absorption of $CO_2$ is essentially zero
in the wavelength range from $0.1\ \mu$m to $1.5\ \mu$m.
A: There is basically no important absorption from atmospheric CO$_2$ in the wavelength range you specify.
This picture, from Patat et al. (2011) identifies the various absorption components looking through the Earth's atmosphere in almost exactly the wavelength range you are interested in. The scale on the left applies to the red (observed) line and the Rayleigh scattering component. The right hand scale applies to the contributions from aerosols and ozone.
There are various molecular lines and bands identified, but these are due to water vapour and molecular oxygen.
The CO$_2$ in the atmosphere will of course make a tiny contribution to the Rayleigh scattering continuum that is roughly proportional to its concentration in the atmosphere compared with oxygen and nitrogen.

