Room Temperature Gas-Phase Detection and Gibbs Energies of Water Amine Bimolecular Complex Formation

Abstract

We have detected the H2O·DMA and H2O·TMA (DMA, dimethylamine; TMA, trimethylamine) bimolecular complexes at room temperature in the gas phase using Fourier transform infrared spectroscopy. For both complexes, five vibrational bands associated with the H2O molecule are observed and assigned. Within a reduced dimensional local mode framework, we set up a six-dimensional model, including the three H2O vibrational modes and three of the six intermolecular modes, all described with internal curvilinear coordinates. The single points on the potential energy surface and Eckart corrected dipole moment surface are calculated with the CCSD­(T)-F12a/cc-pVDZ-F12 method. Combining the measured and calculated transition intensities, we determine the Gibbs energy of complex formation of both complexes from each of the observed bands. The multiple determinations give similar Gibbs energies, for each complex, and increase the confidence in the combined experimental and theoretical approach, and improve the accuracy of the determined Gibbs energies. The average Gibbs energies of complex formation are found to be 5.0 ± 0.2 and 3.8 ± 0.2 kJ/mol for H2O·DMA and H2O·TMA, respectively. In addition to the experimental uncertainty, there is a potential error on the calculated intensities corresponding to 0.4 kJ/mol. However, the small spread among the four determinations suggests that this error is even less. The Gibbs energies of these complexes serve as accurate benchmarks for theoretical approaches that are prevalent in hydrogen bonding and nucleation studies.

Vibrational study of methylamine dimer and hydrated methylamine complexes in solid neon supported by ab initio calculations

“…For H 2 O modes we can attribute the strong observed band at 3379.9 cm -1 to the signature of the O-H hydrogen bond ν 1 with a red shift of 286 cm -1 . In a very recent work in gas phase, this band was observed at 3397 and 3377 cm -1 for the dimethylamine and trimethylamine water complexes, respectively [43]. The complexation lightly disturbs the ν 3 and ν 2 H 2 O modes, the first one is red shifted by 36.7 cm -1 , and the second one blue shifted of the same value 36 cm -1 .…”

Setting up the HyDRA blind challenge for the microhydration of organic molecules

“…115 We see this direct match between electronic structure theory and vibrational spectroscopy as an important complement to more traditional and well-established blind challenges in the field of protein 116 or crystal structure 117 prediction, where subtle energy differences also relate to zero point or thermal vibrational energy and thus anharmonicity treatments, besides getting the potential energy hypersurfaces right. This is even more obvious for the field of room temperature hydration, 118 where an atomistic method which systematically predicts correct free energy differences for a good reason is likely to predict reliable vibrational shifts of monohydrates as well. However, there is a long path of convergence between rigorously atomistic and other, more empirical or approximate or machine-learning models which are more easily extendable to macroscopic samples.…”

A Rather Universal Vibrational Resonance in 1:1 Hydrates of Carbonyl Compounds

“…It might, however, be observed in suitable room temperature gas phase complexes. 47,48 An analogous resonance has not yet been assigned for alcohols as ketone solvents instead of water, 49 but a different resonance was observed slightly below 3500 cm −1 for a double methanol solvate of acetone. 15 This confirms that the robust HOH bend, rather than a variable HOR bend in alcohols, is an essential ingredient to the universality of the resonance position.…”