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.