SH···S H-Bonded Ethanethiol Clusters in Cold Argon and Nitrogen Matrices: An IR Spectroscopic Study

The conformational behavior of SH···S H-bonded ethanethiol (EtSH) dimer and trimer has been experimentally studied in cold and solid argon (Ar) and nitrogen (N₂) matrices via analysis of the ${\nu }_{S-H}$ spectral region. Over 20 spectral bands were observed in both matrices exhibiting a wide range of ${\nu }_{S-H}$ spectral shifts (4.8-87.5 cm^-1). Their spectral assignment was supported by normal mode frequencies calculated at the ωB97X-D/aug-cc-pV(D + d)Z level of theory, which displayed close match. Calculations predicted 24 (EtSH)₂ conformers belonging to four classes (GG, GG', GA, and AA) and 45 (EtSH)₃ conformers from seven classes (GGG, GGG', GG'G', GGA, GG'A, GAA, and AAA) formed by gauche (G and G') and anti (A) monomers. Experimentally, 16 dimers and 9 trimers were identified as the relative stability showed small variation; only 1.42 and 2.77 kcal mol^-1 for dimer and trimer. However, no AA dimer as well as GAA and AAA trimer could be identified in any matrix, due to the presence of multiple lesser stable A monomers. The most stable conformers were found to possess weaker and longer SH···S H-bonds, while the lesser stable conformers possessed stronger and shorter SH···S H-bonds. When compared against SH···S H-bonds in H₂S clusters, the ones in EtSH clusters showed markedly greater contribution of dispersion interaction.