I’m a Physical Chemist. You’re using the wrong equation. The equation you’re using is for calculating the wavelength of the photon EMITTED based on the temperature of the atom it relaxes. i.e. Why does human body temp show up as infrared wavelengths? What you’re trying to talk about is the wavelength ABSORBED by the atom. You need the equation found here. https://byjus.com/photon-energy-formula/ Now. Take the bond energy of a Carbon/Oxygen Double Bond. That’s the only kind that exists in CO2. Use that energy for the energy in the equation above. Make sure to do a dimensional analysis though. The bond energy is likely in kJ/mol. So you’ll need to covert it to the energy of a single atom’s double bond by dividing by Avogadro’s number. Then putting it into the energy equation above. Solve that equation for Lambda to get wavelength. Another thing to keep in mind. When a molecule absorbs a photon it can do a few things. It can transition electrons and then relax them and remit the photon. It can transition electrons, then relax a little, keeping some energy, then emit the rest as a photon. It can transition electrons, then relax by wiggling and rotating keeping it all. In the last case it makes the atom “hotter”. Well then it runs into other gas atoms and can collide with them. It may even give some of its energy to them. Also making them a little “hotter” and itself a little “cooler”. This is exactly how your microwave works to heat your food.