1,721,038 research outputs found
A first glimpse at the acidic proton vibrations in HCl-water clusters via supersonic jet FTIR spectroscopy
No full textThe first mid-IR spectra of the proton vibrational dynamics in isolated HCl-water clusters are presented. Pulsed expansions of HCl and water in rare gases through a slit nozzle are probed by an FTIR spectrometer in the 2000-3300 cm(-1) range. Distinct absorptions by small HCl and HCl water clusters are superimposed on broad bands, partly due to electrolytically dissociated HCl. A firm assignment of the 1 : 1 complex (at 2723.5 cm(-1)) is provided together with a more tentative assignment of the 1 : 2 complex ( near 2464 cm(-1)). The results are compared to condensed phase, matrix isolation and theoretical studies as well as exploratory quantum-chemical calculations. A rationale for the low abundance of small molecular HCl water clusters beyond the 1 : 1 complex is given
Acidic protons before take-off: A comparative jet Fourier transform infrared study of small HCl- and HBr-solvent complexes
No full textA comprehensive study of the proton vibrational dynamics in isolated (HX)(m).(M)(n) (X = Cl, Br, and M = H2O, D2O, CH3OH) clusters is presented. Mid-IR (1900-3900 cm(-1)) spectra are measured in pulsed, seeded slit nozzle expansions. A close similarity among the HCl and HBr systems is revealed and exploited for cluster assignment. Distinct absorptions by small HX and mixed HX-M clusters are superimposed on broadbands, partly due to electrolytically dissociated HX in larger mixed clusters. Assignments of bands corresponding to mixed dimers and trimers based on their X-H and O-H stretching fundamentals are provided. The broad Cl-H stretching band profile of the 1:2 complex is indicative of sub-picosecond intracluster vibrational energy redistribution. The assignments are compared to matrix isolation experiments, when available. Systematic quantum chemistry calculations are performed for HCl-water complexes with up to three molecules and their isotopomers. Hydrogen bond induced frequency shifts of Cl-H stretching vibrations are best described at the coupled-cluster [CCSD(T)] level of theory. Lower level correlated quantum-chemical calculations clearly overestimate Cl-H frequency shifts. The low abundance of mixed clusters in the size range close to electrolytic dissociation (n = 3-5) is discussed. (C) 2003 American Institute of Physics
The influence of embedded atoms, molecules, and clusters on the lifetimes of electron bubbles in large He4 droplets
No full textThe lifetimes of electrons injected into large (approximate to10(6) atoms) superfluid He-4 droplets have been measured in the presence of different prior embedded rare gas atoms, their clusters, and the molecules O-2, H2O, and SF6. For the light rare gas atoms Ne and Ar the lifetimes of about 6.10(-2) s, found previously for pure droplets, are reduced to between 1-2.10(-2) s. Single molecules with large electron affinities, such as SF6 and O-2 and small clusters of H2O lead to a significant increase in the lifetimes. In the case of Kr and Xe, larger clusters with (n) over bar >14 are needed before the lifetimes increase. A simple model, which takes account of the energy levels occupied by the electrons in the corresponding molecules or the clusters, assumed to be solid, can qualitatively explain the observations. (C) 2003 American Institute of Physics
Intramolecular energy transfer between oriented chromophores: High-resolution infrared spectroscopy of HCl trimer
No full textDetailed dynamical and structural information has been obtained for hydrogen-bonded (HCl)(3) clusters via high-resolution IR laser absorption spectroscopy in a supersonic slit expansion. Multiple rovibrational bands in an approximate to3000 cm-1 HCl stretch region have been assigned and analyzed for H Cl-35/H Cl-37 isotopomeric contributions, corresponding to excitation of (i) the degenerate antisymmetric HCl stretch in isotopically pure (H Cl-35)(3), (ii) high- and low-frequency components of the nearly degenerate HCl stretch in H Cl-37 (H Cl-35)(2), (iii) the low-frequency component of the corresponding HCl stretch in (H Cl-37)(2) H Cl-35. The isotopically pure (H Cl-35)(3) results are in good agreement with earlier diode-laser efforts. A simple exciton model for vibrational coupling between HCl subunits is presented that indicates rapid intramolecular energy flow (beta approximate to-1.89 cm-1, tau approximate to 2.8 ps) in the trimer ring, which is in good agreement with vibrationally mediated tunneling rates observed in the HCl dimer. Spectral analysis at slit jet resolution indicates a Deltanuapproximate to120 MHz homogeneous line broadening and an excited-state lifetime of approximate to1.3 ns. The data is consistent with intramolecular vibrational redistribution-induced opening of the trimer followed by true predissociation to either (HCl)(2)+HCl or 3HCl on a longer time scale. (C) 2004 American Institute of Physics
Search for oriented HXeX molecules from the photolysis of HCl and HBr in xenon clusters
No full textThe orientation of free HRgX molecules arising from photodissociation of hydrogen halide molecules HX on rare gas clusters Rgn is investigated in a new experimental arrangement: the rare gas cluster beam with HX molecules in the surface is intersected by two focussed laser beams at one point, where it additionally interacts with a weak electrostatic field. The possibility to generate and successively orient this new class of molecules is analyzed for a couple of new candidate molecules. We observe oriented HXeCl molecules, while HXeBr and HKrCl escaped our detection scheme, as was expected from the analysis. Details of the measured kinetic energy distributions (KED) of H-fragment atoms from the HXeCl photodissociation are analyzed in terms of the Xe–H vibrational structure on the calculated potential energy surface of HXeCl. Finally, a strong indication for observation of HXeH molecules is found in the fragment KED peak around 0.35 eV. These symmetric molecules arise from the dissociation of more than one HX molecule on the cluster and are consistently observed for all HX–Xen systems with X=Cl,Br,I
Ion-molecule reactions in 4He droplets: Flying nano-cryo-reactors
No full textIon-molecule reactions are studied inside large (approximate to10(4) atoms) very cold (0.37 K) superfluid He-4 droplets by mass spectrometric detection of the product ions. He+ ions initially formed inside the droplets by electron impact ionization undergo charge transfer with either embedded D-2, N-2, or CH4. For D-2 this charge transfer process was studied in detail by varying the pickup pressure. For either N-2 or CH4 the reagent ions were formed by this charge transfer and the reaction pathways of the secondary reactions N-2(+)+D-2, CH4++D-2, and CH3++D-2 each with an additionally embedded D-2 molecule were also determined from the pickup pressure dependencies. In several cases, notably He.N-2(+) and CH3D2+ reaction intermediates are observed. The analysis is facilitated by the tendency for molecular ion products to appear without (or with only very few) attached He atoms whereas the atomic ion products usually appear in the mass spectra with several attached He atoms, e.g., He-m.D+ ions with up to m=19. (C) 2005 American Institute of Physics
Comparative FTIR spectroscopy of HX adsorbed on solid water: Ragout-jet water clusters vs ice nanocrystal arrays
No full textIn addition to revealing the stretch-mode bands of the smallest mixed clusters of HCl and HBr (HX) with water, the ragout-jet FTIR spectra of dense mixed water-acid supersonic jets include bands that result from the interaction of HX with larger water clusters. It is argued here that low jet temperatures prevent the water-cluster-bound HX molecules from becoming sufficiently solvated to induce ionic dissociation. The molecular nature of the HX can be deduced directly from the observed influence of changing from HCl to HBr and from replacing H2O with D2O. Furthermore, the band positions of HX are roughly coincidental with bands assigned to molecular HCl and HBr adsorbed on ice nanocrystal surfaces at temperatures below 100 K. It is also interesting that the HX band positions and widths approximate those of HX bound to the surface of amorphous ice films at <60 K. Though computational results suggest the adsorbed HX molecules observed in the jet expansions are weakly distorted by single coordination with surface dangling-oxygen atoms, on-the-fly trajectories indicate that the cluster skeletons undergo large-amplitude low-frequency vibrations. Local HX solvation, the extent of proton sharing, and the HX vibrational spectra undergo serious modulation on a picosecond time scale
Probing hydrogen bond potential surfaces for out-of-plane geometries: Near-infrared combination band torsional (ν6) spectroscopy in (HCl)2
No full textHigh-resolution near-infrared (IR) spectra of jet cooled (HCl)(2) are obtained in the 3000-3070 cm(-1) combination band region corresponding to simultaneous excitation of intermolecular out-of-plane torsion (nu(6)) with intramolecular HCl stretching (nu(1), nu(2)) degrees of freedom. Two ((HCl)-Cl-35)(2) bands (plus the isotopically mixed (HCl)-Cl-35-(HCl)-Cl-37 bands) due to nu(6) torsional excitation are observed. High-resolution spectral analysis of ground-state combination differences and nuclear spin intensity alternation effects permits unambiguous identification of J labeling and tunneling level symmetry, yielding precise rotational constants and vibrational band origins. Comparison with previous far-IR studies suggests assignment of the 3036.52(5) and 3014.86 cm(-1) bands to "bound HCl stretch + torsion'' (nu(2) + nu(6)) combination excitation out of the lower (Gamma(vt) = A(-) <-- A(+)) and upper (&UGamma;(vt) = B- <-- B+) tunneling levels, respectively. A third much weaker band (3035.37 cm(-1)) is also observed in close proximity with the nu(2) + nu(6) (Gamma(vt) = A(-) <-- A(+)) origin, which most likely acquires oscillator strength by state-mixing between the "dark'' perturbing state and the ν(2) + ν(6) upper level. These data provide the first opportunity for comparison with exact quantum calculations by Qui and Bacic and co-workers on high level ab initio/semiempirical (HCl)(2) potential surfaces, which should facilitate further refinement of intermolecular potentials for out-of-plane twisting of the hydrogen bond. (C) 2003 American Institute of Physics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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