PM3, AM1, MINDO3 semi-empirical IR spectra simulations for some nitriles of interest for Titan's chemistry

A set of the semi-empirical methods (PM3. AM1, MNDO and MINDO3) has been tested to find the best auxiliary tool for the identification of nitriles by gas chromatography/Fourier transform IR spectroscopy/mass spectrometry, considering five nitriles of interest for Titan's chemistry as test compounds: acetonitrile, acrylonitrile, cyanoacetylene, 2-butynenitrile and dicyanoacetylene. Of the four semi-empirical methods, MNDO can be considered as the most advantageous auxiliary tool for the gas chromatography/Fourier transform IR spectroscopy/mass spectrometry (GC/FTIR/MS) identification of nitriles of interest for Titan's atmospheric chemistry, since (1) the simulated IR spectra best match the experimental (in some cases AMI gives comparable results); (2) it provides the best linearity between the calculated and experimental frequencies (correlation coefficient of 0.990); a scaling factor of 0.90 Can be applied to afford better correspondence between the calculated and experimental wavenumbers. At the same time, none of the methods is able to predict infrared intensities and a spectral intensity pattern. (C) 2000 Elsevier Science B.V. All rights reserved.