Kinetic study of the proton hydrate H+(H2O)n equilibriums in the gas phase

Investigations of Protonated and Deprotonated Water Clusters Using a Low-Temperature 22-Pole Ion Trap

“…This shell filling effect has been observed in the earliest experiment of Kebarle and co-workers. 15 In Table 1, we also include the results of OH -(H 2 O) 3-7 for comparison with literature values. The listed internal energies of OH -(H 2 O) [3][4][5][6] are averages of the 〈E vib 〉 of DFT-predicted low-energy isomers.…”

“…12 The importance of the latter surely stems from the high abundance of water on earth and the ease of charge separation of the water molecule within clusters, 13 as H 2 O has a high proton affinity of 165 kcal mol -1 and basicity of 157 kcal mol -1 in the gas phase. 14 Experiments with the water cluster ions [H + (H 2 O) n ] go back to the 1970s when the Kebarle group 15 first investigated these ions in a pulsed high-pressure mass spectrometer and deduced the cluster bond energies and other thermochemical quantities from the temperature dependence of equilibrium constants. After emergence of the corona discharge source 3 for production of internally cold clusters, detailed spectroscopic investigations followed, [16][17][18] revealing important structural information for cluster ions of a size up to n ) 8.…”

“…Of special interest in the measurements of Kebarle 15 and other groups [19][20][21][22] is the deviation of the cluster bond energy from a smooth sequence, an indication for the existence of stable structures involving shell closures. The first shell closure was found to occur at n ) 4 for H + (H 2 O) n , 15,19 and the special stability of this cluster ion has since been observed in a number of experiments, including the vibrational predissociation spectroscopic measurements of Yeh et al 16 In addition to the aforementioned bond energy measurements, the temperature-variable 22-pole ion trap also opens new possibilities to obtain temperature-dependent infrared spectra, from which the population of various isomers as a function of temperature can be inferred. For the cluster ions of interest in this work, there exist many structurally as well as energetically similar isomers, and these isomers are separated by barriers with heights comparable to the strength (a few kcal mol -1 ) of the hydrogen bonds that link the water molecules together.…”

Evaluation of Different Implementations of the Thomson Liquid Drop Model: Comparison to Monovalent and Divalent Cluster Ion Experimental Data

“…The free energy change per addition of a single ligand (ΔG n,n-1 ) may be approximated by differentiating the negative of eq 2 with respect to size, n ,53 resulting in (SI units) (5) where the first term is the bulk free energy of vaporization (ΔG vap ), and P 0 is the vapor pressure of L at temperature T. Stepwise binding entropies (ΔS n,n-1 ) are calculated by differentiating eq 5 with respect to temperature (ΔS = −∂ΔG/∂T) holding the internal droplet pressure constant. The approximate sequential binding enthalpies (ΔH n,n-1 ) were obtained from the thermodynamic relationship (6) Results of the C model using physical properties of water at 313 K (Table 1) are shown in Figure 1 for monovalent, divalent, and trivalent ions as a function of cluster size. As expected, higher charge states result in significantly higher calculated ΔH n,n-1 values, and this effect is most pronounced at smaller cluster sizes.…”

“…In ion nanocalorimetry, a measure of the internal energy that is deposited into a cluster upon activation is obtained from the distribution of ligands that are lost from the cluster. For example, electron capture by [Ru(NH 3 ) 6 (H 2 O) 55 ] 3+ results in the loss of 17-19 water molecules from the reduced precursor. 48,49 For large clusters such as this, the recombination energy is determined predominantly from the sum of the ligand binding energies for each water molecule lost.…”