Does any one know what percentage of sunlight is at the particular frequency that CO^2 absorbes?

You want to look up atmospheric trasmissivity and absorption factors for CO2. CO2 absorbs IR wavelengths. Mosquitoes can see in the near IR range. That’s why they can find you witout smelling you first. They can see your CO2 trail. Clever little buggers.
At the lab, we used an IR diode laser shooting through car exhaust to determine the A/F ratio by looking at the absorption of CO and CO2. At certain wavelengths CO2 appears black. See the technical paper I have attached.
There are lots of other papers out there if this is not what you’re looking for. Use google scholar for your search engine.

I found what I needed to know. It does make people more puzzling though.
http://brneurosci.org/co2.html