Knowledge Bank

Ab initio calculation by Searlett and Taylor predicted that S-protonated OCS is more stable than the O-protonated isomer. Experimental evidence appears to contradict this finding. Nakanaga and Amano observed a band of protonated OCS at $3435cm-1$ and assigned it to the O-H stretching vibration. Although they also searched near $2500cm-1$, they didn’t observe any spectrum which could be attributed to an S-protonated isomer. We have carried out ab initio calculation at the MP2/6-311G-+(2df,2pd) and QCISD levels and have confirmed the conclusions of Searlett and Taylor. The S-protonated form is predicted to be more than 4 kcal/mol more stable than the O-protonated isomer. This calculation and the results of our experimental search for the S-protonated will be reported.