An infrared spectroscopic study on gaseous molecular clusters: (Acrylonitrile-methanethiol)(+) and (acrylonitrile-dimethyl sulfide)(+)

The ion-molecule reaction is one of the most important pathways for the formation of new interstellar chemical species. Herein, infrared spectra of cationic binary clusters of acrylonitrile (AN) with methanethiol (CH3SH) and dimethyl sulfide (CH3SCH3) are measured and compared to those previous studies of AN and methanol (CH3OH) or dimethyl ether (CH3OCH3). The results suggest that the ion-molecular reactions of AN with CH3SH and CH3SCH3 only yield products with S center dot center dot center dot HN H-bonded or S(sic)N hemibond structures, rather than the cyclic products as observed in AN-CH3OH and AN-CH3OCH3 studied previously. The Michael addition-cyclization reaction between acrylonitrile and sulfur-containing molecules does not occur due to the weaker acidity of CH bonds in sulfur-containing molecules, which results from their weaker hyperconjugation effect compared to oxygen-containing molecules. The reduced propensity for the proton transfer from the CH bonds hinders the formation of the Michael addition-cyclization product that follows.

Automated summary

The ion-molecule reaction plays a crucial role in the formation of interstellar chemical species. In this study, the infrared spectra of cationic binary clusters of acrylonitrile (AN) with methanethiol (CH3SH) and dimethyl sulfide (CH3SCH3) were measured and compared to previous studies. The results indicate that the ion-molecular reactions of AN with CH3SH and CH3SCH3 produce products with specific bonding structures, unlike the cyclic products observed in previous studies. This is attributed to the weaker acidity of CH bonds in sulfur-containing molecules, which hinders the formation of Michael addition-cyclization products.