The Determination of Absolute Infrared Intensities with a Fourier Transform Spectrometer

Abstract

In principle it is apparent that Fourier transform infrared spectroscopy offers a number of significant advantages in the determination of infrared intensities integrated over the rotational fine structure in vibration-rotation bands. One expects that there should be no problem with photometric accuracy; yet, before embarking on a systematic program of study, we believe it important to establish that the method will work in practice. As a test case we have chosen the V₂ fundamental of CO₂ at 673 cm⁻¹ since this is, in our experience, as difficult a band as any when it comes to measuring integrated intensities. We have, using a Digilab FTS-20 spectrometer, determined a value of the integrated intensity, Γ₂ = 7901 ± 105 cm²/mol which should be compared with the value previously determined on a dispersive instrument, Γ₂ = 7882 ± 110 cm²/mol. We have also determined a value of Γ₃ = 25,300 ± 570 cm²/mol for the integrated intensity of the antisymmetric stretching fundamental.