cross_sections

This script calculates absorption cross sections using anharmonic vibrational frequencies (cm^-1) and infrared (IR) intensities (km/mol), providing a semi-quantitative observable that is more relevant to astronomy than to spectroscopy.

The calculation of absorption cross sections are based on a document by Spanget-Larson and Wikipedia.

Usage

python abs_cross.py freqs.inp

Input/Output

This is the example input from freqs.inp:

3441.7 12
3364 1
1526 43
739.5 107
450 1
423.1 163

The first column shows frequencies in cm^-1 and the second column shows IR intensities in km/mol.

The output absorption cross sections are printed to the screen as follows, again for freqs.inp:

Frequency (cm⁻¹) = Absorption Cross Section (cm²/molecule)
3441.7 = 1.4e-25
3364.0 = 1.2e-26
1526.0 = 8.2e-25
739.5 = 6.5e-24
450.0 = 1.4e-25
423.1 = 2.4e-23