The gas phase infrared spectrum (3250-3810 cm-1) of the singly hydrated ammonium ion, NH4+(H2O), has been recorded by action spectroscopy of mass selected and isolated ions. The four bands obtained are assigned to N-H stretching modes and to O-H stretching modes. The N-H stretching modes observed are blueshifted with respect to the corresponding modes of the free NH4+ ion, whereas a redshift is observed with respect to the modes of the free NH3 molecule. The O-H stretching modes observed are redshifted when compared to the free H2O molecule. The asymmetric stretching modes give rise to rotationally resolved perpendicular transitions. The K-type equidistant rotational spacings of 11.1(2) cm-1 (NH4+) and 29(3) cm-1 (H2O) deviate systematically from the corresponding values of the free molecules, a fact which is rationalized in terms of a symmetric top analysis. The relative band intensities recorded compare favorably with predictions of high level ab initio calculations, except on the nu3(H2O) band for which the observed value is about 20 times weaker than the calculated one. The nu3(H2O)/nu1(H2O) intensity ratios from other published action spectra in other cationic complexes vary such that the nu3(H2O) intensities become smaller the stronger the complexes are bound. The recorded ratios vary, in particular, among the data collected from action spectra that were recorded with and without rare gas tagging. The calculated anharmonic coupling constants in NH4+(H2O) further suggest that the coupling of the nu3(H2O) and nu1(H2O) modes to other cluster modes indeed varies by orders of magnitude. These findings together render a picture of a mode specific fragmentation dynamic that modulates band intensities in action spectra with respect to absorption spectra. Additional high level electronic structure calculations at the coupled-cluster singles and doubles with a perturbative treatment of triple excitations [CCSD(T)] level of theory with large basis sets allow for the determination of an accurate binding energy and enthalpy of the NH4+(H2O) cluster. The authors' extrapolated values at the CCSD(T) complete basis set limit are De [NH4+-(H2O)]=-85.40(+/-0.24) kJ/mol and DeltaH(298 K) [NH4+-(H2O)]=-78.3(+/-0.3) kJ/mol (CC2), in which double standard deviations are indicated in parentheses.

The approach of two atoms with an unpaired electron each results in the formation of a σ bond. Snapshots of the primary step with a large atom‐to‐atom distance and a parallel spin of both electrons and of the final product, consisting of a butterfly structure with a short AlAl σ bond, have been identified for a [R2PAl(PR2)AlPR2] compound using quantum chemical calculations and X‐ray crystallography (see scheme).

A molecular container for a single water molecule was obtained by chemical transformation of a [60]fullerene cage. A phosphate moiety acts as an effective “stopper” in the orifice (see picture).

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Equilibrium geometries and binding energies with respect to the interaction of a methanol molecule (MeOH) with single-walled carbon nanotubes (SWCNTs) of various diameter are calculated by means of density-functional theory including an empirical energy correction for dispersion (DFT-D). This theory is validated by comparing DFT-D results for the model systems benzene−MeOH and coronene−MeOH with corresponding results from high-level wave function-based theory. DFT-D potential energy surface (PES) scans along the intermolecular distance using different functionals are compared with spin-component scaled second-order Møller−Plesset perturbation theory (SCS-MP2) energies and reveal a consistent mutual agreement between the two approaches. Hydrogen-terminated tube sections are used to represent the armchair (4,4), (5,5), (6,6), (8,8), and (10,10) SWCNTs. Similar binding energies are found for the armchair (4,4) and the zigzag (7,0) tubes with similar diameter, but the methanol−SWCNT distance is strongly dependent on the tube type (armchair or zigzag). The interaction energy is found to be diameter-dependent ranging from −15.0 kJ mol-1 for the smallest diameter tube to −20.0 kJ mol-1 for graphene, which represents the limit of a tube with infinite diameter. Calculating the binding energies for differently curved coronene−MeOH models that could be used in a QM/MM approach shows that >90% of the methanol−tube interaction can be captured with this small model. Furthermore, the electronic properties of zigzag tube sections are examined. Because of the termination of the dangling bonds with hydrogen atoms, orbitals arise that are localized at the tube ends and that are not present in the infinitely long SWCNTs. Nevertheless, an approach is presented to extrapolate the band gaps of SWCNTs from gaps calculated within the cluster approach using tube sections of increasing length.