The ease with which the pH of water is measured obscures the fact that there is presently no clear molecular description for the hydrated proton. The mid-infrared spectrum of bulk aqueous acid, for example, is too diffuse to establish the roles of the putative Eigen (H ₃ O ⁺ ) and Zundel (H ₅ O ₂ ⁺ ) ion cores. To expose the local environment of the excess charge, we report how the vibrational spectrum of protonated water clusters evolves in the size range from 2 to 11 water molecules. Signature bands indicating embedded Eigen or Zundel limiting forms are observed in all of the spectra with the exception of the three- and five-membered clusters. These unique species display bands appearing at intermediate energies, reflecting asymmetric solvation of the core ion. Taken together, the data reveal the pronounced spectral impact of subtle changes in the hydration environment.

We report the OH stretching vibrational spectra of size-selected H ⁺ (H ₂ O) _n clusters through the region of the pronounced “magic number” at n = 21 in the cluster distribution. Sharp features are observed in the spectra and assigned to excitation of the dangling OH groups throughout the size range 6 ≤ n ≤ 27. A multiplet of such bands appears at small cluster sizes. This pattern simplifies to a doublet at n = 11, with the doublet persisting up to n = 20, but then collapsing to a single line in the n = 21 and n = 22 clusters and reemerging at n = 23. This spectral simplification provides direct evidence that, for the magic number cluster, all the dangling OH groups arise from water molecules in similar binding sites.

The present study examined the effect of pyrolysis temperature on the physicochemical properties of biochar, activation process and carbon capture. Two different categories of biochars were synthesized from herbaceous (miscanthus and switchgrass) and agro-industrial (corn stover and sugarcane bagasse) feedstock under four different pyrolysis temperatures −500, 600, 700, and 800°C. The synthesized biochars underwent sono-amination activation comprising low-frequency acoustic treatment followed by amine functionalization to prepare adsorbents for CO₂ capture. The highest increment (200%) of CO₂ capture capacity was observed for sono-aminated samples prepared at 600 and 700°C (maximum improvement for miscanthus), while biochars synthesized at 500 and 800°C demonstrated comparatively lesser increment in adsorption capacities that falls in the range of 115–151 and 127–159%, respectively compared to 600 and 700°C. The elevated pyrolysis temperature (particularly 600 and 700°C) resulted in increased %C and %ash contents and reduced %N contents with enhancement of micro surface area and pore volume. Thus, the superior adsorption capacity of miscanthus (at 600 and 700°C) can be attributed to their large surface areas (303–325 m²/g), high carbon contents (82–84%), and low ash contents (4–5%), as well as %N contents after sono-amination that was twice that of raw char.

The arrangement of water molecules around a hydrated electron has eluded explanation for more than 40 years. Here we report sharp vibrational bands for small gas-phase water cluster anions, (H ₂ O) _4-6 ^– and (D ₂ O) _4-6 ^– . Analysis of these bands reveals a detailed picture of the diffuse electron-binding site. The electron is closely associated with a single water molecule attached to the supporting network through a double H-bond acceptor motif. The local OH stretching bands of this molecule are dramatically distorted in the pentamer and smaller clusters because the excited vibrational levels are strongly coupled to the electron continuum. The vibration–to–electronic energy transfer rates, as revealed by line shape analysis, are mode-specific and remarkably fast, with the symmetric stretching mode surviving for less than 10 vibrational periods [50 fs in (H ₂ O) ₄ ^– ].

Chirally sensitive measurement techniques have generally been restricted to bulk samples. Here, we report the observation of fluorescence-detected circular dichroism (FDCD) from single (bridgedtriarylamine) helicene molecules by using an excitation wavelength (457 nanometers) in the vicinity of an electronic transition that shows circular dichroism in bulk samples. The distributions of dissymmetry ( g ) parameters by analysis of signals from pure M - and P -type diastereomers are almost perfect mirror images of one another, each spanning a range of both positive and negative values. In addition, we observe a well-defined structure in the histogram of dissymmetry parameters suggestive of specific molecular orientations at the polymer interface. These single-molecule results highlight strong intrinsic circular dichroism responses that can be obscured by cancellation effects in ensemble measurements of a randomly oriented bulk sample.

Predissociation spectra of the H5O2+∙RGn(RG=Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350–3850cm−1) and shared proton (850–1950cm−1) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H5O2+ [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)], indicating that the symmetrical H5O2+ “Zundel” ion remains largely intact in H5O2+∙Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H5O2+∙Ar, and is dominated by two sharp transitions at 928 and 1047cm−1, with a weaker feature at 1763cm−1. The H5O2+∙Arn,n=1–5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H5O2+ rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H5O2+. These results are consistent with assignment of the strong low-energy bands in the H5O2+∙Ne spectrum to the vibration of the shared proton mostly along the O–O axis, with the 1763cm−1 band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules.