Jonas Lohmann Elkjær Andersen

The effect of hydrogen bonding on torsional dynamics: A combined far-infrared jet and matrix isolation study of methanol dimer

The effect of strong intermolecular hydrogen bonding on torsional degrees of freedom is investigated by far-infrared absorption spectroscopy for different methanol dimer isotopologues isolated in supersonic jet expansions or embedded in inert neon matrices at low temperatures. For the vacuum-isolated and Ne-embedded methanol dimer, the hydrogen bond OH librational mode of the donor subunit is finally observed at ~560 cm(-1), blue-shifted by more than 300 cm(-1) relative to the OH torsional fundamental of the free methanol monomer. The OH torsional mode of the acceptor embedded in neon is observed at ~286 cm(-1). The experimental findings are held against harmonic predictions from local coupled-cluster methods with single and double excitations and a perturbative treatment of triple excitations [LCCSD(T)] and anharmonic. VPT2 corrections at canonical MP2 and density functional theory (DFT) levels in order to quantify the contribution of vibrational anharmonicity for this important class of intermolecular hydrogen bond vibrational motion.

Selective synthesis of clinoatacamite Cu-2(OH)(3)Cl and tenorite CuO nanoparticles by pH control

Copper nanomaterials play a role as catalysts in sustainable energy technology and sensor devices. We present a one-pot synthesis for the selective preparation of phase-pure clinoatacamite (Cu2(OH)3Cl) and cupric oxide (CuO) nanoparticles by controlling the pH of the solution. The effect of pH on the phase of the product was systematically investigated utilizing 2-(N-morpholino)ethanesulfonic acid (MES) buffer. Here, the MES buffer was crucial for the synthesis. It not only allowed for selective synthesis by controlling pH but also guided the morphology of the CuO nanoparticles. In addition, it directed the growth of Cu2(OH)3Cl to provide pure clinoatacamite without the presence of related polymorphs. The products were characterized by transmission electron microscopy, infrared spectroscopy, ultraviolet–visible light spectroscopy, X-ray powder diffraction (XRD), scanning transmission X-ray microscopy and atomic force microscopy. Infrared spectroscopy was essential for characterization of closely related polymorphs of Cu2(OH)3Cl indistinguishable by XRD. A plausible mechanism has been proposed and discussed for the formation of the CuO and Cu2(OH)3Cl nanostructures.

Catchment Areas for Public Transport

This paper on catchment areas used for public transport is from the proceedings of 14th International Conference on Urban Transport and the Environment in the 21st Century, which was held in Malta in 2008. The authors explain that, in the planning of public transport, the catchment areas of stops are often included to estimate the potential number of travelers. They describe different approaches to GIS-based catchment area analyses, including the Circular Buffer approach which is the fundamental, but also the simplest approach; the Service Area approach, which is based on searches in road networks, represents the actual feeder routes, and is a more detailed approach; and the Service Area approach, which can be refined by adding additional resistance to certain points in the road network, e.g. stairways. The authors illustrate differences between the Circular Buffer approach and the Service Area approach and compare the sizes of the resulting catchment areas. One case example illustrates the strength of the Service Area approach and the impact on the catchment area when adding additional time resistance for the crossing of stairways. Another case example illustrates how the additional time resistance in stairways affects the catchment area of an underground station compared to a ground-level station. The benefits of catchment area analyses include improved planning of stops on a new line by calculating travel potential along the line; the prevention of inaccessible areas from being included in the catchment area; and the allowance of detours in feeder routes to/from stations. The authors conclude that GIS-based catchment area analyses are a beneficial multiple decision support tool for the planning of public transport where the level of detail can be suited to the purpose.

The influence of large-amplitude librational motion on the hydrogen bond energy for alcohol–water complexes

The far-infrared absorption spectra have been recorded for hydrogen-bonded complexes of water with methanol and t-butanol embedded in cryogenic neon matrices at 2.8 K. The partial isotopic substitution of individual subunits enabled by a dual inlet deposition procedure provides for the first time unambiguous assignments of the intermolecular high-frequency out-of-plane and low-frequency in-plane donor OH librational modes for mixed alcohol-water complexes. The vibrational assignments confirm directly that water acts as the hydrogen bond donor in the most stable mixed complexes and the tertiary alcohol is a superior hydrogen bond acceptor. The class of large-amplitude donor OH librational motion is shown to account for up to 5.1 kJ mol(-1) of the destabilizing change of vibrational zero-point energy upon intermolecular OHO hydrogen bond formation. The experimental findings are supported by complementary electronic structure calculations at the CCSD(T)-F12/aug-cc-pVTZ level of theory.

Spectroscopic identification of ethanol-water conformers by large-amplitude hydrogen bond librational modes.

The far-infrared absorption spectra have been recorded for hydrogen-bonded complexes of water with ethanol embedded in cryogenic neon matrices at 2.8 K. The partial isotopic H/D-substitution of the ethanol subunit enabled by a dual inlet deposition procedure enables the observation and unambiguous assignment of the intermolecular high-frequency out-of-plane and the low-frequency in-plane donor OH librational modes for two different conformations of the mixed binary ethanol/water complex. The resolved donor OH librational bands confirm directly previous experimental evidence that ethanol acts as the O⋯HO hydrogen bond acceptor in the two most stable conformations. In the most stable conformation, the water subunit forces the ethanol molecule into its less stable gauche configuration upon dimerization owing to a cooperative secondary weak O⋯HC hydrogen bond interaction evidenced by a significantly blue-shift of the low-frequency in-plane donor OH librational band origin. The strong correlation between the low-frequency in-plane donor OH librational motion and the secondary intermolecular O⋯HC hydrogen bond is demonstrated by electronic structure calculations. The experimental findings are further supported by CCSD(T)-F12/aug-cc-pVQZ calculations of the conformational energy differences together with second-order vibrational perturbation theory calculations of the large-amplitude donor OH librational band origins.

Competition between weak OH⋯π and CH⋯O hydrogen bonds: THz spectroscopy of the C2H2—H2O and C2H4—H2O complexes

THz absorption spectra have been recorded for the weakly bound molecular complexes of H2O with C2H4 and C2H2 embedded in cryogenic neon matrices at 2.8 K. The observation and assignment of a large-amplitude acceptor OH librational mode of the C2H2-H2O complex at 145.5 cm-1 confirms an intermolecular CH⋯O hydrogen-bonded configuration of C2v symmetry with the H2O subunit acting as the hydrogen bond acceptor. The observation and assignment of two large-amplitude donor OH librational modes of the C2H4-H2O complex at 255.0 and 187.5 cm-1, respectively, confirms an intermolecular OH⋯π hydrogen-bonded configuration with the H2O subunit acting as the hydrogen bond donor to the π-cloud of C2H4. A (semi)-empirical value for the change of vibrational zero-point energy of 4.0-4.1 kJ mol-1 is proposed and the combination with quantum chemical calculations at the CCSD(T)-F12b/aug-cc-pVQZ level provides a reliable estimate of 7.1 ± 0.3 kJ mol-1 for the dissociation energy D0 of the C2H4-H2O complex. In addition, tentative assignments for the two strongly infrared active OH librational modes of the ternary C2H4-HOH-C2H4 complex having H2O as a doubly OH⋯π hydrogen bond donor are proposed at 213.6 and 222.3 cm-1. The present findings demonstrate that the relative stability of the weak hydrogen bond motifs is not entirely rooted in differences of electronic energy but also to a large extent by differences in the vibrational zero-point energy contributions arising from the class of large-amplitude intermolecular modes.

Probing the global potential energy minimum of (CH2O)2: THz absorption spectrum of (CH2O)2 in solid neon and para-hydrogen

The true global potential energy minimum configuration of the formaldehyde dimer (CH2O)2, including the presence of a single or a double weak intermolecular CH⋯O hydrogen bond motif, has been a long-standing subject among both experimentalists and theoreticians as two different energy minima conformations of Cs and C2h symmetry have almost identical energies. The present work demonstrates how the class of large-amplitude hydrogen bond vibrational motion probed in the THz region provides excellent direct spectroscopic observables for these weak intermolecular CH⋯O hydrogen bond motifs. The combination of concentration dependency measurements, observed isotopic spectral shifts associated with H/D substitutions and dedicated annealing procedures, enables the unambiguous assignment of three large-amplitude infrared active hydrogen bond vibrational modes for the non-planar Cs configuration of (CH2O)2 embedded in cryogenic neon and enriched para-hydrogen matrices. A (semi)-empirical value for the change of vibrational zero-point energy of 5.5 ± 0.3 kJ mol-1 is proposed for the dimerization process. These THz spectroscopic observations are complemented by CCSD(T)-F12/aug-cc-pV5Z (electronic energies) and MP2/aug-cc-pVQZ (force fields) electronic structure calculations yielding a (semi)-empirical value of 13.7 ± 0.3 kJ mol-1 for the dissociation energy D0 of this global potential energy minimum.

Structure determination of a novel metal-organic compound synthesized from aluminum and 2,5-pyridinedicarboxylic acid

The structure of [Al 2 (pydc) 2 (μ 2 -OH) 2 (H 2 O) 2 ] n (pydc = 2,5-pyridinedicarboxylate) was successfully determined from powder X-ray diffraction data. The compound crystallizes in the triclinic system (space group P -1) with a = 6.7813(1) A, b = 7.4944(1) A, c = 8.5013(1) A, α = 95.256(1)°, β = 102.478(1)°, γ = 108.979(1)°. The structure consists of aluminum ions coordinating N and O in distorted octahedra, sharing an edge through two hydroxide ions. These dinuclear complexes are connected by pydc ions, which at one end coordinate by nitrogen and oxygen and only by oxygen at the other end. The pydc orientation is reversed in the neighboring pydc, forming double stranded chains interconnected by the aluminum dinuclear complexes in a ladder-like arrangement along [001].

Alignment Analysis of Urban Railways Based On Passenger Travel Demand

This paper on an alignment analysis of urban railways based on passenger travel demand is from the proceedings of the 12th International Conference on Computer System Design and Operation in Railways and Other Transit Systems, held in Beijing, China, in 2010. The authors stress that travel demand is a good foundation for evaluating a railway alignment for its ability to attract passengers. They present a computerized, GIS-based methodology that can be used as decision support for selecting the best alignment for Metro or light rail transit. The methodology calculates travel potential within defined buffers surrounding the alignment. The methodology offers three different approaches depending on the desired level of detail: a simple line potential approach that performs corridor analysis, a detailed catchment area analysis based on stops on the alignment, or a refined service area analysis that uses search distances in street networks. The authors conclude that all three approaches produce trustworthy results and can be applied as decision support in different stages of the urban railway alignment planning process.