The present study reports temperature dependent rate constants k 1 for the title reaction across the temperature range 213 to 293 K obtained in a Knudsen flow reactor equipped with an external free radical source based on the reaction C 2 H 5 I + H •  → C 2 H 5 •  + HI and single VUV-photon ionization mass spectrometry using Lyman- α radiation of 10.2 eV. Combined with previously obtained high-temperature data of k 1 in the range 298–623 K using the identical experimental equipment and based on the kinetics of C 2 H 5 • disappearance with increasing HI concentration we arrive at the following temperature dependence best described by a three-parameter fit to the combined data set: k 1 = (1.89 ± 1.19)10 −13 ( T /298) 2.92±0.51 exp ((3570 ± 1500)/ RT ), R = 8.314 J mol – 1 K – 1 in the range 213–623 K. The present results confirm the general properties of kinetic data obtained either in static or Knudsen flow reactors and do nothing to reconcile the significant body of data obtained in laminar flow reactors using photolytic free radical generation and suitable free radical precursors. The resulting rate constant for wall-catalyzed disappearance of ethyl radical across the full temperature range is discussed. Highly correlated ab initio quantum chemistry methods and canonical transition state theory were applied for the reaction energy profiles and rate constants. Geometry optimizations of reactants, products, molecular complexes, and transition states are determined at the CCSD/cc-pVDZ level of theory. Subsequent single-point energy calculations employed the DK-CCSD(T)/ANO-RCC level. Further improvement of electronic energies has been achieved by applying spin-orbit coupling corrections towards full configuration interaction and hindered rotation analysis of vibrational contributions. The resulting theoretical rate constants in the temperature range 213–623 K lie in the range E-11–E-12 cm 3 molecule – 1 s – 1 , however experiments and theoretical modelling seem at great odds with each other.

Publicly Available October 2, 2015

Collisional Relaxation of NCN: An Experimental Study with Laser-Induced Fluorescence

Jens Hetzler, Matthias Olzmann

Page range: 1503-1519

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Abstract

Collisional relaxation of NCN produced by photolysis of NCN 3 at a wavelength of 248 nm has been investigated with laser-induced fluorescence (LIF) in a temperature range of 240–293 K and a pressure range of 10–800 mbar with different bath gases (He, Ne, Ar, Kr, H 2 , N 2 , O 2 , and N 2 O). LIF excitation spectra were recorded, and LIF intensity-time profiles experimentally obtained at an excitation wavelength of 329.01 nm have been fitted with biexponential functions. The pressure and bath gas dependence of the rate coefficients obtained was rationalized in terms of a simple Landau–Teller/Schwartz–Slawsky–Herzfeld model, and notable influences of vibrational energy transfer to the rate of the overall relaxation process have been found. Evidence was obtained for a two-channel vibrational relaxation in NCN.

September 18, 2015

Reaction of Chlorine Molecules with Unsaturated Submicron Organic Particles

Denisia M. Popolan-Vaida, Chen-Lin Liu, Theodora Nah, Kevin R. Wilson, Stephen R. Leone

Page range: 1521-1540

Abstract

The reaction of closed shell Cl 2 molecules with sub-micron droplets composed of unsaturated molecules, oleic acid (OA), linoleic acid (LA), linolenic acid (LNA), or squalene (Sqe), are investigated in an atmospheric pressure flow tube reactor in conjunction with a vacuum ultraviolet photoionization aerosol mass spectrometer and a scanning mobility particle sizer. Cl 2 is found to react with all particles, and the reactive uptake coefficients depend on the number of unsaturated reaction sites, e.g., γ Cl2 Sqe = (0.66 ± 0.03) × 10 −4 versus γ Cl2 OA = (0.23 ± 0.01) × 10 −4 . In addition, the chemical evolution of squalene and its chlorinated products reveal that the reaction becomes slower for higher chlorinated products.

August 14, 2015

Theoretical Kinetics Study of the Reactions Forming the ClCO Radical Cycle in the Middle Atmosphere of Venus

Carlos J. Cobos, Adela E. Croce

Page range: 1541-1559

Abstract

A quantum-chemistry and kinetics study of key chemical reactions involved in the ClCO radical cycle of the Venus atmosphere: Cl + CO + M → ClCO + M (1); ClCO + O 2 + M → ClC(O)OO + M (2) and ClC(O)OO + Cl → CO 2 + ClO + Cl (3) ( M = CO 2 ), has been performed at 150–300 K. Unimolecular reaction rate theories on potential energy features derived at the G4//B3LYP/6-311+G(3df) ab initio composite level were employed. Limiting low pressure rate coefficients calculated for Reaction (1) are in good agreement with recommended experimental values. The present results validate rate coefficient values measured for Reaction (2) over relevant strato-mesosphere Venusian conditions. Rate coefficients calculated by the SACM/CT for Reaction (3) are given by k 3 = 2.5 × 10 −11 ( T /300) 0.5  cm 3 molecule – 1 s – 1 . In the absence of experimental data, these values provide the first reliable prediction for k 3 .

August 28, 2015

On the Relation between Population Kinetics and State-to-State Rate Coefficients for Vibrational Energy Transfer

Elena I. Dashevskaya, Ilya Litvin, Evgeny E. Nikitin

Page range: 1561-1574

Abstract

The relation between time-dependent population of vibrational state and collision-induced state-to-state rate coefficients is discussed within the Landau–Teller kinetic equations for the relaxation of harmonic oscillators in a heat bath. In particular, the increase of the populations in the first and the second vibrational state of an initially cold oscillator shows a considerable variety of its relation to a single Landau–Teller state-to-state rate coefficient. It is suggested that this variety should be kept in mind when experimental studies of the relaxation of specific level are analyzed.

October 8, 2015

Investigation of the ν₂ + 2ν₃ Subband in the Overtone Icosad of ¹³CH₄ by Pulsed Supersonic Jet and Diode Laser Cavity Ring-Down Spectroscopy: Partial Rovibrational Analysis and Nuclear Spin Symmetry Conservation

Zoran Bjelobrk, Carine Manca Tanner, Martin Quack

Page range: 1575-1607

Abstract

We have investigated the ν 2 + 2 ν 3 combination band of methane 13 CH 4 centered at 7493.15918 cm – 1 within the icosad of the overtone absorption. The jet-CRD setup combining supersonic jet expansions and cavity ring-down spectroscopy which was already used for the reinvestigation of the same spectral region for the main isotope of methane ( 12 CH 4 ) has been used to record spectra of the Q and R branches at room temperature as well as at very low temperatures (down to 4 K). Based on our previous temperature-dependent investigations and the present results, we provide a careful analysis and the assignment for lines involving angular momentum quantum numbers up to J = 4. The analysis of the relative intensities in spectra taken at various rotational and effective translational temperatures demonstrate conservation of nuclear spin symmetry for 13 CH 4 under the conditions of a supersonic jet expansion, similar to our previous results regarding 12 CH 4 and also to further results using other techniques and covering other spectral ranges. This is in agreement with theoretical expectation regarding very slow nuclear spin symmetry relaxation under these conditions in supersonic jet expansions.

September 11, 2015

The Rotationally-Resolved Absorption Spectrum of Formaldehyde from 6547 to 7051 cm⁻¹

Albert A. Ruth, Uwe Heitmann, Elke Heinecke, Christa Fittschen

Page range: 1609-1624

Abstract

We report new experimental data on the rotationally resolved room temperature absorption spectrum of CH 2 O in the near infrared (NIR) region between 6804 and 7051 cm – 1 (1470–1418 nm). Data have been obtained by cavity enhanced absorption spectroscopy and complement the spectrum in the wavelength range 6547–6804 cm – 1 , obtained using virtually the same experimental set-up and already published in an earlier publication (Staak et al., J. Mol. Spectrosc. 229 (2005) 115–121). Several vibrational combination bands occur in this region and give rise to a congested spectrum and over 4500 lines with cross-sections over 5 · 10 – 23 cm 2 were observed. Recent experimental studies using NIR absorption spectroscopy for quantifying CH 2 O in different chemical systems indicate that the absorption cross-sections obtained by Staak et al. may have been overestimated. The results of these experiments are reviewed here and a recommendation for absolute absorption cross sections of CH 2 O in the NIR range will be given. Absolute absorption cross-sections stated here are corrected by the recommended factor.

July 31, 2015

Constraining the Conformational Landscape of a Polyether Building Block by Raman Jet Spectroscopy

Sebastian Bocklitz, Martin A. Suhm

Page range: 1625-1648

Abstract

Collisionally induced chain isomerization of CH 3 OCH 2 CH 2 OCH 3 around its three central torsional angles is characterized in a supersonic slit jet by probing compound-seeded carrier gas expansions with focussed 5–25 W cw 532 nm radiation as a function of carrier gas, nozzle temperature and distance. Spontaneously Raman scattered photons are collected and dispersed down to 100 cm – 1 . They reveal important contributions from three chain conformations in the expansion. Isomerization around the outer torsional angle is found to be feasible, whereas the central OCCO angle remains largely conserved under most expansion conditions. The spectroscopic results are used for a critical assessment of quantum-chemical predictions for the energy sequence of the three low-lying conformations. The stretched global minimum energy structure of this polyether building block is consistent with a statistical model of the dominant unimolecular relaxation pathways.

July 10, 2015

The Reaction Kinetics of Amino Radicals with Sulfur Dioxide

Yide Gao, Peter Glarborg, Paul Marshall

Page range: 1649-1661

Abstract

Application of the laser photolysis–laser-induced fluorescence method to the reaction NH 2  + SO 2 in argon bath gas yields pressure-dependent, third-order kinetics which may be summarized as k = (1.49 ± 0.15) × 10 −31 ( T /298 K) −0.83  cm 6 molecule – 2 s – 1 over 292–555 K, where the uncertainty is the 95% confidence interval and includes possible systematic errors. The quenching of vibrationally excited NH 2 is consistent with a high-pressure limit for NH 2  + SO 2 of (1.62 ± 0.25) × 10 −11  cm 3 molecule – 1 s – 1 over the temperature range 295–505 K, where again the 95% confidence interval is shown. Ab initio analysis yields a H 2 N–SO 2 dissociation enthalpy of 73.5 kJ mol – 1 , and comparison with RRKM theory and the exponential down model for energy transfer yields 〈 ΔE 〉 down = 350 cm – 1 for Ar at room temperature.

July 10, 2015

Challenging High-Level ab initio Rovibrational Spectroscopy: The Nitrous Oxide Molecule

Benjamin Schröder, Peter Sebald, Christopher Stein, Oskar Weser, Peter Botschwina

Page range: 1663-1690

Abstract

The equilibrium structure and rovibrational energies of nitrous oxide (N 2 O) in its electronic ground state ( X 1 Σ + ) are derived from a high-level ab initio potential energy function (PEF). This PEF is based on a composite approach with the basic contribution given by explicitly correlated coupled-cluster (CC) calculations. Smaller contributions include corrections due to inner-shell correlation, scalar-relativistic effects and higher-order correlation up to iterative pentuple excitations (CCSDTQP in CC nomenclature). The high importance of higher-order correlation in order to reach the desired accuracy led to the use of an extrapolation scheme to approximately account for the effect of hextuple and some pentuple excitations. A reasoning for the soundness of the method is given in this work. The results of the rovibrational calculations are compared to those of two multi-reference (MR) based composite PEFs, where the basic contribution is given by MR configuration interaction and MR average coupled-pair functional calculations. A highly accurate electric dipole moment function is also computed by the three composite methods in excellent agreement with the experimental values available. Subtle irregularities in the intensity pattern are reproduced in great detail and several kinds of resonances are analyzed without the need to empirically adjust our best ab initio PEF. The equilibrium bond lengths were determined by a mixed experimental/theoretical approach yielding R e (NN) = 1.12695(10) Å and R e (NO) = 1.18539(5) Å.

October 2, 2015

Reaction of the CF₃ Radical with Various Cations (Ar⁺, Xe⁺, O₂⁺, NO⁺, CO₂⁺, C₂F₅⁺)

Nicholas S. Shuman, Justin P. Wiens, Jordan C. Sawyer, Shaun G. Ard, Oscar Martinez Jr., Thomas M. Miller, Albert A. Viggiano

Page range: 1691-1707

Abstract

The kinetics of reactions of the trifluoromethyl radical (CF 3 ) with several simple cations (Ar + , Xe + , O 2 + , NO + , CO 2 + , C 2 F 5 + ) are studied via the variable electron and neutral density attachment mass spectrometry (VENDAMS) technique. CF 3 is produced via dissociative electron attachment to CF 3 I, resulting in radical concentrations that are smaller than produced using pyrolysis methods, but better quantified. Rate constants and product branching fractions are reported, with typical uncertainties of ∼ 30%. Three of the reactions, Ar + , O 2 + , and C 2 F 5 + proceed near the calculated collisional rate constant, while the other reactions are between 10% – 30% efficient. The inefficiency of the reactions of Xe + and CO 2 + can be explained by the reactions strictly obeying spin-conservation. The reaction of Ar + yields predominantly (90%) CF 2 + via dissociative charge transfer, with a minor channel to CF 3 + . The reaction of C 2 F 5 + yields predominantly CF 3 + with a second channel (∼ 25%) yielding C 2 F 4 + and CF 4 , the only example here of a bond-breaking and bond-making reaction. For the other four reactions, only charge transfer to yield CF 3 + is observed. Rate constants for these same ions with CF 3 I are also reported and found to be rapid with a variety of products formed.

July 3, 2015

Electronic Spectra of Corannulenic Cations and Neutrals in Neon Matrices and Protonated Corannulene in the Gas Phase at 15 K

Corey A. Rice, Jan Fulara, Iryna Garkusha, Ádám Nagy, François-Xavier Hardy, Oliver Gause, John P. Maier

Page range: 1709-1728

Abstract

Three absorption systems starting at 624.1, 601.2, and 590.0 nm were detected in a 6 K neon matrix following deposition of mass selected m / z = 250 ions produced from corannulene vapour in a hot cathode ion source. The two latter systems were also observed after deposition of neutral corannulene in solid neon with concomitant bombardment of the matrix with argon ions. The features in the absorption spectrum are assigned to the 4 2 A′′ ← X 2 A′′ transition of cylobutadieno-benzo[ghi]fluoranthene cation and to the 3 2 A′ ← X 2 A′′ and 3 2 A′′ ← X 2 A′ transitions of two Jahn-Teller structures of bowl-shaped corannulene cations, respectively. The assignment is based on excitation energies calculated with the SAC-CI and CASPT2 methods. The electronic absorption spectrum of protonated corannulene has onsets at 515.1 and 398.8 nm in a neon matrix, following deposition of a mass-selected beam produced by reactions of corannulene with EtOH 2 + . The absorptions are assigned, on the basis of theoretical predictions, to the 3,4 1 A ← X 1 A transitions. The electronic spectrum was also recorded in the gas phase using a resonant multiphoton fragmentation technique in an ion trap at vibrational and rotational temperatures of 15 K. The 3,4 1 A ← X 1 A transitions are observed with origin bands at 521 ± 1 nm and 396.4 ± 0.1 nm. The 3 1 A excited electronic state indicates fast internal conversion of ≈ 5 fs, while the 4 1 A state has a lifetime of ≈ 0.2 ps. A distinct vibrational pattern is discernible in the 4 1 A ← X 1 A transition.

Publicly Available July 10, 2015

Photoionization Yields in Intense fs-Laser Fields – A Systematic Investigation of Chirp Effects

Nicola Reusch, Steffen Griebe, Johannes Karges, Karl-Michael Weitzel

Page range: 1729-1746

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Abstract

The femtosecond laser ionization of several small hydrocarbon molecules (methane, ethane, propane) has been investigated as a function of the second order spectral phase (linear chirp) of laser pulses centered at λ = 807 nm. Ion yields are demonstrated to depend markedly on the linear chirp parameter. At laser intensities exceeding 5 · 10 14 W/cm 2 the ionization characteristics resemble an intensity-driven process, i.e. the largest ion yield is observed for a close to transform-limited laser pulse. For smaller laser intensities a pronounced sign effect in the chirp dependence appears, i.e. the maximum ion yield is observed for a negative linear chirp parameter of several hundred to thousand fs 2 . We suggest that this sign effect is connected to the anharmonicity of the electronic potentials involved. This suggestion is supported by the fact that basically no sign effect in the chirp dependence is observed for the noble gases argon, krypton and xenon. We further suggest that the electronic polarizability and structure plays some role as methanol does not show a marked sign-dependent chirp effect.

October 2, 2015

Determination of the Temperature-Dependent OH⁻ (H₂O) + CH₃I Rate Constant by Experiment and Simulation

Jing Xie, Michael J. Scott, William L. Hase, Peter M. Hierl, Albert A. Viggiano

Page range: 1747-1763

Abstract

Experimental and simulation studies of the OH – (H 2 O) + CH 3 I reaction give temperature dependent rate constants which are in excellent agreement. Though there are statistical uncertainties, there is an apparent small decrease in the rate constant as the temperature is increased from − 60 to 125 ℃, and for this temperature range the rate constant is ∼ 1.6 times smaller than that for the unsolvated reactants OH –  + CH 3 I. Previous work [J. Phys. Chem. A 117 (2013) 14019] for the unsolvated reaction found that the S N 2 and proton transfer pathways, forming CH 3 OH + I – and CH 2 I –  + H 2 O, have nearly equal probabilities. However, for the microsolvated OH – (H 2 O) + CH 3 I reaction the S N 2 pathways dominate. An important contributor to this effect is the stronger binding of H 2 O to the OH – reactant than to the proton transfer product CH 2 I – , increasing the barrier for the proton transfer pathway. The effect of microsolvation on the rate constant for the OH – (H 2 O) 0,1  + CH 3 I reactions agrees with previous experimental studies for X – (H 2 O) 0,1  + CH 3 Y reactions. The simulations show that there are important non-statistical attributes to the entrance- and exit-channel dynamics for the OH – (H 2 O) + CH 3 I reaction.

July 3, 2015

Can we Observe Gas Phase Nucleation at the Molecular Level?

Jorge J. Ferreiro, Thomas E. Gartmann, Bernhard Schläppi, Ruth Signorell

Page range: 1765-1780

Abstract

We propose and discuss an experiment for the study of neutral gas phase nucleation on a molecular level using propane as the condensable gas. The experiment combines a uniform Laval expansion with soft mass spectrometric detection. The uniform Laval expansion allows nucleation experiments under well-defined conditions while the mass spectrometric detection provides molecular-level information on the molecular aggregates formed. It is discussed how one could observe the onset of nucleation and retrieve the size of the critical nucleus from the mass spectra.

June 5, 2015

Multiphoton Ionization of Liquid-to-Supercritical Methanol. Ultrafast Dynamics of Electron Localization and Geminate Recombination

Annika Gehrmann, Peter Vöhringer

Page range: 1781-1798

Abstract

Solvated electrons have been generated by 150 fs, 266 nm multiphoton ionization of methanol and their primary dynamics have been recorded through near-infrared transient absorption over a wide temperature (294 K ≤ T ≤ 523 K) and pressure (90 bar ≤ p ≤ 523 bar) region corresponding to the liquid and the supercritical phases of the solvent. On ultrashort time scales well below a few tens of picoseconds, the dynamics of electron localization, solvation, and thermalization reveal themselves as a delayed rise of the spectroscopic signal originating from the fully equilibrated solvated electron. The temperature-dependence of these dynamics is in line with a thermally-activated process involving hydrogen-bond breakage and formation that is induced by the librational/torsional dynamics of the methanol molecules. Longer time scales of up to 1 ns are governed by the dynamics of geminate recombination whose temperature dependence is indicative of multiple competing recombination pathways involving charged and neutral species, including radicals, of yet to be determined nature.

July 10, 2015

Femtosecond Infrared Spectroscopy of Aroylperoxide Photofragmentation – Site Selective Decarboxylation

Hendrik Vennekate, Christian Reichardt, Arne Walter, Harald Fuest, Jörg Schroeder, Dirk Schwarzer

Page range: 1799-1814

Abstract

The ultrafast photofragmentation of acetyl-benzoyl peroxide (ABPO) and 2-naphthoyl-benzoyl peroxide (NBPO) after UV excitation at 266 nm is studied by mid-infrared transient absorption spectroscopy. 13 C-isotopic labelling is employed to unravel the primary fragmentation paths. For NBPO it appears that excitation of the benzoyloxy part causes decarboxylation exclusively at that site. In ABPO the acetyloxy part completely decarboxylates upon 266 nm excitation while only 80% – 85% of the benzoyloxyl radicals formed decarboxylate. The remaining radicals either combine with methyl radicals to methylbenzoate within about 30 ps or survive on the time scale of the experiment (1.5 ns). Photofragmentation of ABPO occurs from the S 1 -state whose lifetime is about 200 fs. All fragmentation products including CO 2 also appear on this time scale.

July 24, 2015

Excited State Dynamics of Selected All-trans C₄₀ Xanthophyll Carotenoids

Florian Ehlers, Mirko Scholz, Thomas Lenzer, Kawon Oum

Page range: 1815-1830

Abstract

We investigated the excited state dynamics of selected all- trans C 40 xanthophyll carotenoids by ultrafast pump-supercontinuum probe (PSCP) spectroscopy in the spectral range 350–770 nm upon photoexcitation by a femtosecond laser ( ca. 80 fs pulse length) near 500 nm in acetone. The following carotenoids were selected considering a systematic variation of the number and position of carbonyl (CO) and hydroxyl (OH) functional groups on the β -ionone rings and the change of the effective conjugation length of the polyene system: β -cryptoxanthin (1), echinenone (2), 3-hydroxyechinenone (3), 3′-hydroxyechinenone (4), canthaxanthin (5), adonirubin (6) and astaxanthin (7). The carotenoids featuring an increasing conjugation length, for example, (1), (3) and (6), showed a systematically shorter S 1 lifetime of 8.7, 6.2 and 4.7 ps, respectively. Carotenoids with OH groups adjacent to a CO group showed slightly broader steady-state and transient absorption bands, but the influence on the S 1 lifetime was minor compared to the case of CO substitution. Moreover, in all cases we observed clearly visible “S * signals”, namely a longer-lived characteristic S 0  → S 2 red-edge absorption and a negative signal in the S 0  → S 2 bleach region. This spectral signature is assigned to highly vibrationally excited molecules in the ground electronic state S 0 * which are generated by internal conversion from S 1 . The S 0 * species cool with a time constant of 9.2–9.6 ps in the case of the keto-substituted carotenoids (2)–(7), whereas we obtain a larger value of 13.2 ps for (1) which does not have a keto group. Our findings are supported by results from a global kinetic analysis procedure.

September 25, 2015

Complexation and Chiral Recognition of Chiral Binaphthyl Derivatives and β-Cyclodextrins in Solution Probed by Triplet Excited State Relaxation

Yasser M. Riyad, Christian Laube, Sergej Naumov, Ralf Hermann, Bernd Abel

Page range: 1831-1853

Abstract

It is well known in supramolecular chemistry that cyclodextrin host molecules (CDs) are capable of including and binding guest molecules in their hydrophobic cavities via non-covalent interactions. The unique recognition capability of CDs depends on their inherent asymmetric cavities. We explored here the impacts of the chiral recognition of excited triplet state of guest 1,1′–Binaphthyl–2,2′–diylhydrogenphosphate (BNP) enantiomers by host native β –cyclodextrin ( β –CD) and chemically modified Heptakis(2,3,6–tri–O–methyl)– β –cyclodextrin (TMe– β –CD). For this regard, UV-Vis, fluorescence, and laser flash photolysis spectroscopy were performed and our experimental results were flanked by density functional theory (DFT) calculations. Triplet decay dynamics of BNP enantiomers were investigated in the absence and presence of cyclodextrins under different conditions and the chiral recognition behavior is discussed based on the obtained kinetic and spectral data of excited triplet state. Here we show that the long lived triplet excited states (as opposed to the singlet states) and its relaxation in solution may be a sensitive probe to detect chiral recognition. The ability of TMe– β –CD to recognize axial chirality is superior to that of β –CD. These findings may be attributed to the asymmetric cavities of cyclodextrins, which determines the degree of interaction. The differences in the triplet behavior of R– and S–BNP(T 1 )–TMe– β –CD may arise from the different orientations of the guest molecule within the twisted and restricted TMe– β –CD cavity. We assume here that the orientation of the more favorable enantiomer (S–BNP(T 1 )) is geometrically preferable, while a similar orientation of the less favorable enantiomer (R–BNP(T 1 )) might be hindered by steric reasons. In contrast, the triplet dynamics of BNP enantiomers within the unrestricted macrocyclic β –CD ring are similar. This might be ascribed to a similar orientation and interaction and ultimately relaxation of both enantiomers within a round and undistorted β –CD cavity, suggesting the formation of similar inclusion complexes. These findings are evidence for the possibility to detect chiral recognition and interaction as well as tiny structural differences in the BNP complexes within cyclodextrin cavities via laser flash photolysis technique.

August 21, 2015

Ionic Solutions Probed by Resonant Inelastic X-ray Scattering

Zhong Yin, Ivan Rajkovic, Sreevidya Thekku Veedu, Sascha Deinert, Dirk Raiser, Rohit Jain, Hironobu Fukuzawa, Shin-ichi Wada, Wilson Quevedo, Brian Kennedy, Simon Schreck, Annette Pietzsch, Philippe Wernet, Kyoshi Ueda, Alexander Föhlisch, Simone Techert

Page range: 1855-1867

Abstract

X-ray spectroscopy is a powerful tool to study the local charge distribution of chemical systems. Together with the liquid jet it becomes possible to probe chemical systems in their natural environment, the liquid phase. In this work, we present X-ray absorption (XA), X-ray emission (XE) and resonant inelastic X-ray scattering (RIXS) data of pure water and various salt solutions and show the possibilities these methods offer to elucidate the nature of ion-water interaction.

June 26, 2015

Ordering Phenomena in Surfactant Systems: From Micellar Solutions to Gel and Crystalline Phases

Holger Gibhardt, Chandrashekara R. Haramagatti, Ahmed Kh. Islamov, Oleksandr I. Ivankov, Alexander I. Kuklin, Götz Eckold

Page range: 1869-1885

Abstract

The phase behavior of surfactant systems is investigated using alkyltrimethylammonium bromide surfactants with different alkyl chain lengths (dodecyl-, tetradecyl-, hexadecyl- and octadecyl) as model substances. The transitions between micellar solution, gel-phase and crystalline phase are characterized by the combination of Raman spectroscopy and small angle neutron scattering. It is demonstrated that in systems with small surfactant molecules the aqueous solution crystallizes directly on cooling to form hydrated crystals while an intermediate gel phase is observed in long chain systems. The cross-over is found for the hexadecyl-compound where the gel phase appears only at high concentrations.

August 28, 2015

Investigation of the Growth Behaviour of Cobalt Thin Films from Chemical Vapour Deposition, Using Directly Coupled X-ray Photoelectron Spectroscopy

Patrick Hervé Tchoua Ngamou, Achraf El Kasmi, Theodor Weiss, Henning Vieker, André Beyer, Volkmar Zielasek, Katharina Kohse-Höinghaus, Marcus Bäumer

Page range: 1887-1905

Abstract

Thin films and coatings are a basis for many technological processes, including microelectronics, electrochemistry and catalysis. The successful deposition of metal films and nanoparticles by chemical vapour deposition (CVD) needs control over a number of physico-chemical processes such as precursor and substrate selection, delivery, temperature, pressure and flow conditions. Here, cobalt thin films were deposited by means of pulsed-spray evaporation chemical vapour deposition (PSE-CVD) from ethanol solutions of Co(acac) 2 and Co(acac) 3 on bare glass and silicon substrates. The physico-chemical properties of the grown films were characterised by XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and HIM (helium ion microscopy). Co(acac) 2 enabled the growth of cobalt metal at lower temperatures than Co(acac) 3 . The difference in deposition temperature was attributed to the ability of ethanol to reduce Co(acac) 2 better than Co(acac) 3 . In addition, the film deposited from Co(acac) 2 exhibited a higher metal content and a less porous structure than that deposited from Co(acac) 3 . Increasing the substrate temperature enhanced the carbon content because of the thermal decomposition of both precursors. Using a nickel seed layer improved the growth rate until a critical temperature of 360 ℃, at which the thermal decomposition of the precursor becomes predominant. A decrease in the deposition temperature when using the nickel seed layer was only observed with Co(acac) 2 precursor; the growth behaviour under these conditions was monitored with a unique UHV-compatible PSE-CVD reactor directly attached to an XPS system and ascribed to an enhancement of its catalytic reduction by ethanol.

August 14, 2015

Ultrafast Dynamics of the Indoline Dye D149 on Mesoporous ZnO and Al₂O₃ Thin Films

Oliver Flender, Peter W. Lohse, Juan Du, Torsten Oekermann, Mirko Scholz, Kawon Oum, Thomas Lenzer

Page range: 1907-1928

Abstract

Ultrafast photoinduced electron injection and subsequent relaxation steps of the indoline dye D149 were investigated for mesoporous thin films using pump–supercontinuum probe (PSCP) transient absorption spectroscopy in the range 370–770 nm. Three types of mesoporous ZnO layers were compared: Electrodeposited ZnO thin films prepared by using the structure-directing agents (1) Eosin Y (EY) and (2) Coumarin 343 (C343), which are known to produce ZnO layers of different morphology; and (3) mesoporous ZnO thin films consisting of sintered nanoparticles with a diameter of 20 nm. As a reference system, we used a “non-injecting” mesoporous thin film with large band-gap, consisting of Al 2 O 3 nanoparticles with a diameter of 50 nm. On all ZnO thin films, D149 efficiently injects electrons. We observed two components, a dominant one with τ ≤ 70 fs (time-resolution-limited) and a slower one with a time constant of 250–350 fs. Fast initial charge separation is also consistent with the immediate appearance of oscillatory structure due to a change in refractive index of ZnO upon electron injection. For all ZnO thin films, we observe a transient shift of the spectra with a time constant of ca. 20 ps which is assigned to a transient Stark effect (= electrochromism). The S 0 → S 1 absorption band of D149 is shifted due to the build-up of a local electric field between dye radical cations and ZnO conduction band electrons. On longer timescales, step-scan FTIR spectroscopy revealed a slightly faster cation-electron recombination on ZnO/C343 than on ZnO/EY thin films. On Al 2 O 3 , metastable close cation-electron pairs are formed initially which recombine afterwards, and no transient Stark effect is observed. Complementary PSCP experiments on D149 in the ionic liquid [C 2 mim] + [N(CN) 2 ] – show that D149 is ideally suited for solar cell applications because of its long S 1 lifetime of 590 ps. In addition, biphasic solvation dynamics are observed in this IL with a subpicosecond component and a much slower component related to the viscosity of the IL which is well described by a stretched exponential.

July 3, 2015

Observation of Translation-to-Vibration Excitation in Acetylene Scattering from Au(111): A REMPI Based Approach

Kai Golibrzuch, Joshua H. Baraban, Pranav R. Shirhatti, Jörn Werdecker, Christof Bartels, Alec M. Wodtke

Page range: 1929-1949

Abstract

We present quantum-state and velocity resolved experiments for molecular beam scattering of acetylene (C 2 H 2 ) from a single-crystal Au(111) surface, observations that reveal translational, rotational and vibrational inelasticity. The experiments are made possible by a novel (1 + 2) REMPI scheme for acetylene. The scattered molecules' velocity distributions as well as their ro-vibrational quantum-state distributions depend on the translational energy of incidence, E I , providing unambiguous evidence that the scattered molecules were not trapped and equilibrated on the surface. We report the E I -dependence of the collisional excitation of one and two quanta of the trans -bending vibrational mode, ν 4 = 0 → 1, 2, which is consistent with a mechanism involving conversion of incidence translational energy to acetylene vibration. Rotationally resolved velocity measurements on scattered acetylene in its ground vibrational state are interpreted in terms of orientation-dependent rotational and vibrational excitation probabilities.

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Objective
Zeitschrift für Physikalische Chemie (ZPC), founded in 1887, covers the main developments in physical chemistry with emphasis on experimental and theoretical research. It represents a combination of reaction kinetics and spectroscopy, quantum theory, surface research and electrochemistry, thermodynamics and structure analysis of matter in its various conditions. Short times for peer review and publication can be guaranteed for high quality submissions.

Topics

reaction kinetics
spectroscopy
surface research
electrochemistry
thermodynamics
structure analysis

Article formats
Original paper, review paper

> Information on submission process

Volume 229 Issue 10-12 - Special Issue: Progress in Chemical Kinetics, Dynamics and Spectrosopy / Bernd Abel, Dirk Schwarzer, Karl-Michael Weitzel

Issue of Zeitschrift für Physikalische Chemie

Frontmatter

Congratulations to Jürgen Troe

The Kinetics of the Reaction C2H5• + HI → C2H6 + I• over an Extended Temperature Range (213–623 K): Experiment and Modeling

Abstract

Collisional Relaxation of NCN: An Experimental Study with Laser-Induced Fluorescence

Abstract

Reaction of Chlorine Molecules with Unsaturated Submicron Organic Particles

Abstract

Theoretical Kinetics Study of the Reactions Forming the ClCO Radical Cycle in the Middle Atmosphere of Venus

Abstract

On the Relation between Population Kinetics and State-to-State Rate Coefficients for Vibrational Energy Transfer

Abstract

Investigation of the ν2 + 2ν3 Subband in the Overtone Icosad of 13CH4 by Pulsed Supersonic Jet and Diode Laser Cavity Ring-Down Spectroscopy: Partial Rovibrational Analysis and Nuclear Spin Symmetry Conservation

Abstract

The Rotationally-Resolved Absorption Spectrum of Formaldehyde from 6547 to 7051 cm−1

Abstract

Constraining the Conformational Landscape of a Polyether Building Block by Raman Jet Spectroscopy

Abstract

The Reaction Kinetics of Amino Radicals with Sulfur Dioxide

Abstract

Challenging High-Level ab initio Rovibrational Spectroscopy: The Nitrous Oxide Molecule

Abstract

Reaction of the CF3 Radical with Various Cations (Ar+, Xe+, O2+, NO+, CO2+, C2F5+)

Abstract

Electronic Spectra of Corannulenic Cations and Neutrals in Neon Matrices and Protonated Corannulene in the Gas Phase at 15 K

Abstract

Photoionization Yields in Intense fs-Laser Fields – A Systematic Investigation of Chirp Effects

Abstract

Determination of the Temperature-Dependent OH− (H2O) + CH3I Rate Constant by Experiment and Simulation

Abstract

Can we Observe Gas Phase Nucleation at the Molecular Level?

Abstract

Multiphoton Ionization of Liquid-to-Supercritical Methanol. Ultrafast Dynamics of Electron Localization and Geminate Recombination

Abstract

Femtosecond Infrared Spectroscopy of Aroylperoxide Photofragmentation – Site Selective Decarboxylation

Abstract

Excited State Dynamics of Selected All-trans C40 Xanthophyll Carotenoids

Abstract

Complexation and Chiral Recognition of Chiral Binaphthyl Derivatives and β-Cyclodextrins in Solution Probed by Triplet Excited State Relaxation

Abstract

Ionic Solutions Probed by Resonant Inelastic X-ray Scattering

Abstract

Ordering Phenomena in Surfactant Systems: From Micellar Solutions to Gel and Crystalline Phases

Abstract

Investigation of the Growth Behaviour of Cobalt Thin Films from Chemical Vapour Deposition, Using Directly Coupled X-ray Photoelectron Spectroscopy

Abstract

Ultrafast Dynamics of the Indoline Dye D149 on Mesoporous ZnO and Al2O3 Thin Films

Abstract

Observation of Translation-to-Vibration Excitation in Acetylene Scattering from Au(111): A REMPI Based Approach

Abstract

The Kinetics of the Reaction C₂H₅^• + HI → C₂H₆ + I^• over an Extended Temperature Range (213–623 K): Experiment and Modeling

Investigation of the ν₂ + 2ν₃ Subband in the Overtone Icosad of ¹³CH₄ by Pulsed Supersonic Jet and Diode Laser Cavity Ring-Down Spectroscopy: Partial Rovibrational Analysis and Nuclear Spin Symmetry Conservation

The Rotationally-Resolved Absorption Spectrum of Formaldehyde from 6547 to 7051 cm⁻¹

Reaction of the CF₃ Radical with Various Cations (Ar⁺, Xe⁺, O₂⁺, NO⁺, CO₂⁺, C₂F₅⁺)

Electronic Spectra of Corannulenic Cations and Neutrals in Neon Matrices and Protonated Corannulene in the Gas Phase at 15 K

Determination of the Temperature-Dependent OH⁻ (H₂O) + CH₃I Rate Constant by Experiment and Simulation

Excited State Dynamics of Selected All-trans C₄₀ Xanthophyll Carotenoids

Ultrafast Dynamics of the Indoline Dye D149 on Mesoporous ZnO and Al₂O₃ Thin Films