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.