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The hydroxyarene (ROH molecules) band which has large solvent-induced solvatochromic spectral shifts was investigated. Findings showed that the ground state has a negligible dipole moment and a weak ROH***S bond. When excited to S1, both its dipole moment and its acidity rise rapidly. Hence, the hydrogen-bond strengthens substantially while the remaining solvent molecules rearrange to make way for the enhanced dipole.

The infrared (IR) spectrum of the ammoniated ammonium dimer is more complex than those of the larger protonated ammonia clusters due to close-lying fundamental and combination bands and possible Fermi resonances (FR). To date, the only theoretical analysis involved partial dimensionality quantum nuclear dynamic simulations, assuming a symmetric structure (D3d) with the proton midway between the two nitrogen atoms. Here we report an extensive study of the less symmetric (C3v) dimer, utilizing both second order vibrational perturbation theory (VPT2) and ab initio molecular dynamics (AIMD), from which we calculated the Fourier transform (FT) of the dipole-moment autocorrelation function (DACF). The resultant IR spectrum was assigned using FTed velocity autocorrelation functions (VACFs) of several interatomic distances and angles. At 50 K, we have been able to assign all 21 AIMD fundamentals, in reasonable agreement with MP2-based VPT2, about 30 AIMD combination bands, and a difference band. The combinations involve a wag or the NN stretch as one of the components, and appear to follow symmetry selection rules. On this basis, we suggest possible assignments of the experimental spectrum. The VACF-analysis revealed two possible FR bands, one of which is the strongest peak in the computed spectrum. Raising the temperature to 180 K eliminated the "proton transfer mode" (PTM) fundamental, and reduced the number of observed combination bands and FRs. With increasing temperature, fundamentals red-shift, and the doubly degenerate wags exhibit larger anharmonic splittings in their VACF bending spectra. We have repeated the analysis for the H3ND+NH3 isotopologue, finding that it has a simplified spectrum, with all the strong peaks being fundamentals. Experimental study of this isotopologue may thus provide a good starting point for disentangling the N2H7+ spectrum. [ABSTRACT FROM AUTHOR]

Research into excited-state photon transfer from an ultrafast photoacid, 5-cyano-2-naphthol, is presented. It was found that the reaction obeys the mechanism of geminate diffusion control over the entire composition range.

Protonatedwater clusters that are hydrogen-bonded to a neutralbenzene molecule are a reductionist model for protons at hydrophobicsurfaces, which are of fundamental importance in biological energytransduction processes. Of particular interest is the protonated waterdimer (“Zundel ion”) on benzene, whose gas-phase messengerIR spectrum has been previously interpreted in terms of an asymmetricbinding of the protonated water dimer to the benzene ring througha single water molecule. This “standing Eigen” isomerhas a hydronium core. We have found an alternative “crouchingZundel” isomer, which attaches to the benzene ring symmetricallyvia both of its water molecules. When Ar-tagged, it has an IR spectrumin much better agreement with experiment than the standing Eigen isomer,particularly at the lower frequencies. These conclusions are basedon static harmonic (and anharmonic) normal-mode analysis using densityfunctional theory with various (dispersion corrected) functionalsand particularly on dynamic anharmonic spectra obtained from the dipoleautocorrelation functions from classical ab initio molecular dynamicswith the BLYP, PBE, and B3LYP functionals. Possible implications toprotons on water/organic-phase interfaces are discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Atomic radii can be calculated from ionization energies. [•] Slater theory without the Slater rules. [•] Effective single-electron atomic model. [ABSTRACT FROM AUTHOR]

Super-photoacids, such as 5-cyano-2-naphthol, tend to undergo excited-sate proton transfer within their chromophore, when subjected to a series of time-resolved fluorescence. An empirical analysis involving the Kamlet-Taft approach indicate that majority of the shifting phenomenon in the excitation spectra is made possible through the action of hydrogen bonds, which have been donated from the OH group. The hydrogen bond contained by super-photoacids has also been shown to gather intensity during the excited state.