False Lines due to Folding in Fourier Transform Spectroscopy

The phenomenon of false lines due to folding in Fourier Transform Spectroscopy is explained using by Nyquist sampling theorem The characters of false lines are discussed. The key to avoid false lines is to use suitable filters to remove the signal outside the wanted spectral region. Two kinds of filters, optical and electrpnic filters namely, are compared to serve this purpose. It is found out that both kind of filters should be combined in order to prevent folding as well as secure a good signal to noise ratio. Some experimental parameters setting rules are advanced. The method proved to be successful in our experiments of recording the v= 3 and v=4 highly vibrational spectra of arsine.