Infrared spectra of some matrix isolated organoisothiocyanate molecules

The infrared (3500 to 300 cm−1) spectra of methylisothiocyanate, ethylisothiocyanate, isopropylisothiocyanate, and cyclopropylisothiocyanate isolated in argon and nitrogen matrices have been recorded. In general, the spectra were more complex in the nitrogen matrices and, for ethylisothiocyanate, nearly all of the fundamentals appeared as doublets in the nitrogen matrix but for the most part as single bands in the argon matrix. No evidence could be found for a second conformer for either ethylisothiocyanate or isopropylisothiocyanate. Even though cyclopropylisothiocyanate has been shown to exist as the cis and trans conformers at ambient temperature, little conclusive evidence could be found for two isomers in the infrared matrix material. The complex spectra observed in the NCS antisymmetric stretching region as well as in the 520 cm−1 region appear to arise in part from combinations involving the low-frequency large amplitude CNC bend or asymmetric torsion of these organoisothiocyanate molecules. It appears that the vibrational spectra of these molecules are not sensitive to the orientation of the NCS moiety.