# The line spectrum of carbon dioxide

#### Question P9.2.5

The HITRAN database provides a list of molecular line intensities for modeling radiative transmission in planetary atmospheres. Its native format consists of 160-character records of fixed-width fields.

Use pandas to read in the file CO2-transitions.par. This text file contains fixed-width fields; the relevant fields are in character columns 4 – 15 (wavenumber, $\tilde{\nu}$, in $\mathrm{cm^{-1}}$) and columns 16 – 25 (spectral line intensity, $S$, at 296 K in $\mathrm{cm^{-1}/(molecule\,cm^{-2})}$, weighted by isotopologue abundance). Note: these column numbers are indexed starting at 1.

Plot line intensity against wavelength for these transitions in the infrared region of the spectrum ($\lambda$ = 1 μm to 20 μm, corresponding to wavenumber $\tilde{\nu} = 500\;\mathrm{cm^{-1}}$ to $10\,000\;\mathrm{cm^{-1}}$), where carbon dioxide ($\mathrm{CO_2}$) is responsible for a significant fraction of the greenhouse effect in Earth's atmosphere.

Hint: Use Matplotlib's stem plotting function.

#### Solution

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