H-Bonded Clusters in the Trimethylamine/Water System: A Matrix Isolation and Computational Study

The environmentally important interaction products of trimethylamine (TMA) and water molecules have been observed by Matrix Isolation Fourier Transform Infrared Spectroscopy (MIS-FTIR). Infrared spectra of solid argon matrix layers, in which both TMA and H₂O molecules were entrapped as impurities, were analyzed for bands in the ν­(O–H) region, not seen in matrix layers containing either of the parent molecules alone. Results were interpreted on the basis of the emergence of several spectral band pairs and their red shifts from the position of the matrix isolated H₂O monomers as compared to semiempirically scaled frequencies from the B3LYP/aug-cc-pVTZ calculations and empirical correlations with a large body of data on H-bonded complexes. Bands were assigned to a complex cluster of two TMA molecules flanking a closed ring of four H-bonded H₂O molecules. The formation of this cluster is argued to be formed in the vapor phase (as opposed to being a result of diffusion of the trapped species) and is related to its large stabilization energy (enthalpy) because of strong cooperative effects in its H-bond system.