Observation of the Low‐Frequency Spectrum of the Water Trimer as a Sensitive Test of the Water‐Trimer Potential and the Dipole‐Moment Surface

Abstract

Intermolecular interactions in bulk water are dominated by pairwise and non‐pairwise cooperative interactions. While accurate descriptions of the pairwise interactions are available and can be tested by precise low‐frequency spectra of the water dimer up to 550 cm −1 , the same does not hold for the three‐body interactions. Here, we report the first comprehensive spectrum of the water trimer in the frequency region from 70 to 620 cm −1 using helium‐nanodroplet isolation and free‐electron lasers. By comparison to accompanying high‐level quantum calculations, the experimentally observed intermolecular bands can be assigned. The transition frequencies of the degenerate translation, the degenerate in‐plane and the non‐degenerate out‐of‐plane libration, as well as additional bands of the out‐of‐plane librational mode are reported for the first time. These provide a benchmark for state‐of‐the‐art water potentials and dipole‐moment surfaces, especially with respect to three‐body interactions.

Calculating Reliable Gibbs Free Energies for Formation of Gas-Phase Clusters that Are Critical for Atmospheric Chemistry: (H2SO4)3

“…In addition, moving from the F12 method to the Riemann and 4-5 CBS methods reveals that extrapolation to the CBS using the correlated double, triple, and quadruple basis sets result in another several kcal mol –1 increase in Gibbs free energy. The Riemann and 4-5 CBS results are virtually identical relative to the expected error in this method of less than a kcal mol –1 . − These differences in Δ G ° will have a profound effect on efforts to calculate the initial growth of pre-nucleation complexes as Δ G ° values are combined with concentrations of monomers in the atmosphere to predict the pathways for nucleation to occur. , …”

Flipping Kinetics of the Water Trimer on Acenaphthylene: Persistence of a Highly Dipolar ddd Configuration at Interstellar Temperatures

“…For these complexes, some O–H···π interactions appear to be responsible for the water trimer anchoring in the Ace plane, as can be realized in top views of Figure a–d. Considering an isolated water trimer, it is well-known that it prefers to be in ddu or udd configurations; ,− then it is plausible that these configurations first approach the Ace plane (Figure a–c). The unusual case is the complexation of a ddd configuration with the aromatic plane (Figure d).…”

“…Our energetic parameters calculated at the M06-2X/6-311++G(d,p) level of theory are summarized in Table 7. For the isolated water trimer, the most studied process in the literature refers to the ddu ↔ duu inversion, 33,[49][50][51]54,55 since the free ddd configuration is one exhibiting high energy and may exist only at special conditions. 33,53 Figure 4 displays our energetic profile for the forward reaction on Ace, including the ZPVE.…”

Using Car-Parrinello simulations and microscopic order descriptors to reveal two locally favored structures with distinct molecular dipole moments and dynamics in ambient liquid water

“…The previous studies 44 attribute the bands between 125-180 cm -1 to the intermolecular stretchingvibrational modes of hydrogen-bonded water dimers 44,69,70 . Furthermore, experiments 71 suggest that the intermolecular vibrations between 190 and 220 cm -1 can be attributed to hindered translations of water molecules within a tetrahedral network. Moreover, a peak at 203 cm -1 has been observed in experiments for supercooled water and attributed to the tetrahedral structure 72 .…”