NEAR-INFRARED SPECTROSCOPY OF SMALL PROTONATED WATER CLUSTERS

Small protonated water clusters and their argon tagged analogues of the general formula H$^{+}$(H$_{2}$O)$_{n}$Ar$_{m}$ have been generated in a pulsed electric discharge source. Clusters containing $n=1-8$ water molecules were mass-selected and their absorptions in the near-infrared were probed with a tunable Nd$colon$YAG pumped OPA/OPA laser system in the region from 4850$-$7350 cm$^{-1}$. A doublet corresponding to overtones of the free O$-$H stretches of the external waters was observed around 7200 cm$^{-1}$ that was continuously decreasing in intensity with increasing cluster size. Broad, mostly featureless absorptions were found around 5300 cm$^{-1}$ associated with stretch/bend combinations and with the hydrogen bonded waters in the core of the clusters. Vibrational assignments were substantiated by comparison to anharmonic frequency computations via second-order vibrational perturbation theory (VPT2) at the MP2/aug-cc-pVTZ level of theory

AN ARGON-OXYGEN COVALENT BOND IN THE ArOH+ MOLECULAR ION

Although the OH$^{+}$ cation is decidedly a triplet ($^{3}\Sigma^{-}$) being over 50 kcal mol$^{-1}$ more stable than the corresponding singlet ($^{1}\Delta$), binding to an argon atom can reverse this situation. The noble gas forms a strong donor-acceptor bond to the excited state singlet cation with a bond strength of 66.4 kcal mol$^{-1}$ at the CCSDT(Q)/CBS level of theory. This makes the singlet 3.9 kcal mol$^{-1}$ more stable than the most favorable triplet Ar$-$HO$^{+}$ complex. In a cold molecular beam experiment we have prepared both, singlet and triplet, isomers of this molecular ion depending on the employed ion source. Photodissociation spectroscopy in combination with messenger atom tagging reveals that the two observed spin isomers exhibit completely different spectral signatures in the infrared and the O$-$H stretching fundamentals differ by about 900 \wn. These findings might encourage the search for a new potential interstellar noble gas molecule

GAS PHASE INFRARED SPECTROSCOPY OF ISOMERIC BENZYL AND TROPYLIUM CATIONS

The isomeric benzyl and tropylium C$_{7}$H$_{7}$$^{+}$ cations have been of great interest to physical organic and gaseous ion chemists for many decades. Still, infrared spectroscopic characterization of these ions in the gas phase could so far only be achieved for their methylated derivatives but not for the C$_{7}$H$_{7}$$^{+}$ ions themselves. Thus, we set out to produce both relevant isomers of this elusive ion in a cold molecular beam experiment through ionization of different precursor molecules comprising the preformed 6- and 7-membered rings. We measured their IR spectra via photodissociation with a tunable OPO/OPA laser system in combination with the argon messenger atom technique. The obtained spectra were assigned with the aid of second order vibrational perturbation theory utilizing dispersion-corrected density functional theory. \vspace{0.1cm} \begin{center} \includegraphics[width=0.3\textwidth]{benzyl.eps} \end{center

Mechanical properties of nanosheets and nanotubes investigated using a new geometry independent volume definition

Cross-sectional area and volume become difficult to define as material dimensions approach the atomic scale. This limits the transferability of macroscopic concepts such as Young's modulus. We propose a new volume definition where the enclosed nanosheet or nanotube average electron density matches that of the parent layered bulk material. We calculate the Young's moduli for various nanosheets (including graphene, BN and MoS2) and nanotubes. Further implications of this new volume definition such as a Fermi level dependent Young's modulus and out-of-plane Poisson's ratio are shown

An evaluation of Bradfordizing effects

The purpose of this paper is to apply and evaluate the bibliometric method Bradfordizing for information retrieval (IR) experiments. Bradfordizing is used for generating core document sets for subject-specific questions and to reorder result sets from distributed searches. The method will be applied and tested in a controlled scenario of scientific literature databases from social and political sciences, economics, psychology and medical science (SOLIS, SoLit, USB Köln Opac, CSA Sociological Abstracts, World Affairs Online, Psyndex and Medline) and 164 standardized topics. An evaluation of the method and its effects is carried out in two laboratory-based information retrieval experiments (CLEF and KoMoHe) using a controlled document corpus and human relevance assessments. The results show that Bradfordizing is a very robust method for re-ranking the main document types (journal articles and monographs) in today’s digital libraries (DL). The IR tests show that relevance distributions after re-ranking improve at a significant level if articles in the core are compared with articles in the succeeding zones. The items in the core are significantly more often assessed as relevant, than items in zone 2 (z2) or zone 3 (z3). The improvements between the zones are statistically significant based on the Wilcoxon signed-rank test and the paired T-Test

Preserving cultural heritage: Analyzing the antifungal potential of ionic liquids tested in paper restoration

Early industrialization and the development of cheap production processes for paper have led to an exponential accumulation of paper-based documents during the last two centuries. Archives and libraries harbor vast amounts of ancient and modern documents and have to undertake extensive endeavors to protect them from abiotic and biotic deterioration. While services for mechanical preservation such as ex post de-acidification of historic documents are already commercially available, the possibilities for long-term protection of paper-based documents against fungal attack (apart from temperature and humidity control) are very limited. Novel processes for mechanical enhancement of damaged cellulosic documents use Ionic Liquids (IL) as essential process components. With some of these ILs having azolefunctionalities similar to well-known fungicides such as Clotrimazole, the possibility of antifungal activities of these ILs was proposed but has not yet been experimentally confirmed. We evaluated the potency of four ILs with potential application in paper restoration for suppression of fungal growth on five relevant paper-infesting molds. The results revealed a general antifungal activity of all ILs, which increased with the size of the non-polar group. Physiological experiments and ultimate elemental analysis allowed to determine the minimal inhibitory concentration of each IL as well as the residual IL concentration in process-treated paper. These results provide valuable guidelines for IL-applications in paper restoration processes with antifungal activity as an added benefit. With azoles remaining in the paper after the process, simultaneous repair and biotic protection in treated documents could be facilitated

Ripple edge engineering of graphene nanoribbons

It is now possible to produce graphene nanoribbons (GNRs) with atomically defined widths. GNRs offer many opportunities for electronic devices and composites, if it is possible to establish the link between edge structure and functionalisation, and resultant GNR properties. Switching hydrogen edge termination to larger more complex functional groups such as hydroxyls or thiols induces strain at the ribbon edge. However we show that this strain is then relieved via the formation of static out-of-plane ripples. The resultant ribbons have a significantly reduced Young's Modulus which varies as a function of ribbon width, modified band gaps, as well as heterogeneous chemical reactivity along the edge. Rather than being the exception, such static edge ripples are likely on the majority of functionalized graphene ribbon edges.Comment: Supplementary Materials availabl

Low energy graphene edge termination via small diameter nanotube formation

We demonstrate that free graphene sheet edges can curl back on themselves,reconstructing as nanotubes. This results in lower formation energies than any other non-functionalised edge structure reported to date in the literature. We determine the critical tube size and formation barrier and compare with density functional simulations of other edge terminations including a new reconstructed Klein edge. Simulated high resolution electron microscopy images show why such rolled edges may be difficult to detect. Rolled zigzag edges serve as metallic conduction channels, separated from the neighbouring bulk graphene by a chain of insulating sp$^3$-carbon atoms, and introduce Van Hove singularities into the graphene density of states.Comment: To appear in Phys. Rev. Let

Mechanical properties of nanosheets and nanotubes investigated using a new geometry independent volume definition

Abstract Cross-sectional area and volume become difficult to define as material dimensions approach the atomic scale. This limits the transferability of macroscopic concepts such as Young's modulus. We propose a new volume definition where the enclosed nanosheet or nanotube average electron density matches that of the parent layered bulk material. We calculate the Young's moduli for various nanosheets (including graphene, BN and MoS 2 ) and nanotubes. Further implications of this new volume definition such as a Fermi level dependent Young's modulus and out-of-plane Poisson's ratio are shown