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

The environmentally important interaction products of trimethylamine (TMA<b>)</b> 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 <i>band pairs</i> 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