Experimental and computational study of isotopic effects within the Zundel ion

Proton and deuteron position preferences in water clusters: An ab initio study

“…Extrapolating this principle to its extreme, we would expect to find the strongest preference for H in the shortest known H bond, which is the centrosymmetric bond of the Zundel cation. The results of Devlin et al 26 nicely bear out this extrapolation. Figure 1 presents a scatter diagram of b OH * vs ⌬ZPE͕H * ͖ for six of the 18 categories.…”

“…Since ZPE is ͑up to the harmonic approximation͒ proportional to the sum of a cluster's vibrational frequencies and since H-to-D substitution has different effects on spectra depending on which H is replaced, 33,34 positional isotope effects in water clusters should be common. The ZPE calculation for the Zundel cation is quite difficult because its energy as a function of the bonding proton's position is strongly anharmonic, but Devlin et al 26 succeeded at demonstrating the basis for the positional isotope effect favoring H as mentioned above, through diffusion Monte Carlo techniques.…”

“…However, D does not always prefer to be in H bonds: A recent experimental and theoretical study of the Zundel cation H 5 O 2 + found that for H 5 O 2 + drawn from a 3 : 1 molar mix of D 2 O and H 2 O at 80 K, H was 2.3 times as likely to occupy the bonding position as chance would predict. 26 Ab initio studies of finite systems including both H 2 O and D 2 O have been scarce. Gregory and Clary's study of the benzene-water heterodimer 27 included the isotopic variants and noted that the C 6 H 6 -D-O-H form has lower energy than the C 6 H 6 -H-O-D form, consistent with the experimental results of Gutowsky et al 28 and Pribble and Zwier.…”

Assigning Predissociation Infrared Spectra of Microsolvated Hydronium Cations H3O+⋅(H2)n (n=0, 1, 2, 3) by Ab Initio Molecular Dynamics

“…[44] However, the AIMD results reveal a prominent temperature dependence for this spectral feature, [49,51] and hence it could be speculated that the temperature dependence of classical nuclear dynamics underlying such AIMD simulations may have hampered earlier studies [52][53][54][55] in reproducing (even qualitatively) the doublet feature. Studies on the influence of the messengers on the spectra additionally must deal with a sufficiently accurate description of the weak intermolecular interactions within the employed electronic structure method and, importantly, sufficient sampling of the vast phase space accessible to these floppy systems at finite temperature.…”

“…Despite the significant a priori approximations introduced by using approximate electronic structure theory ("on the fly") in conjunction with classical dynamics of nuclear motion, it has been demonstrated [49,51] that the AIMD approach to theoretical IR spectroscopy can qualitatively reproduce even the intricate doublet feature of bare H 5 O 2 + and its isotopologues compared to quasi-exact MCTDH calculations. [44] However, the AIMD results reveal a prominent temperature dependence for this spectral feature, [49,51] and hence it could be speculated that the temperature dependence of classical nuclear dynamics underlying such AIMD simulations may have hampered earlier studies [52][53][54][55] in reproducing (even qualitatively) the doublet feature.…”