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The intramolecular vibrational energy redistribution (IVR) and the intermolecular vibrational energy transfer (VET) of benzene tolune (CH3-C6H5) and alpha, alpha, alpha,-trifluorotoluene (CF3-C6H5) selectivity excited in overtones or combination bands of C-H stretch vibrations in solution are investigated using transition femtosecond IR-pump-UV-probe spectroscopy. The study revealed the effects of a methyl rotor and the effect of methyl rotor fluorination on the mechanisms and time scales of IVR and VET in aromatic model systems.

A novel approach for rapid product screening of fast reactions in IR-laser-heated liquid microbeams in a vacuum is highlighted. It is observed that small amounts of radicals but no ionic intermediates other than simple proton adducts are detected.

Selectively excited benzene and toluene in the gas and solution phase are investigated with ultrafast transient absorption spectroscopy to study the impact of a solvent on the time scales of intramolecular vibrational energy redistribution (IVR). The findings indicate that an internal rotor accelerates IVR in the gas phase significantly whereas the effect appears to be largely concealed in solution.

The intramolecular vibrational energy redistribution (IVR) and the intermolecular vibrational energy transfer (VET) of selectively excited aromatic molecules in solution (CF2CICFCI2) are observed by femtosecond IR-pump-UV-probe spectroscopy. A characteristic variation of the relaxation dynamics of the aromatic systems upon chemical substitution is observed.

The study of intermolecular vibrational energy redistribution (IVR) and intermolecular vibrational energy transfer (VET) of two alkyl iodides (CF3CH2I and CH3CH2I) selectively excited in the two quanta overtone region of the CH stretch vibration are measured in real time in solution. The effect of chemical substitution on the mechanisms and time scales of IVR and VET rate coefficients for both molecules is focused.

In the present article a novel approach for rapid product screening of fast reactions in IR-laser-heated liquid microbeams in a vacuum is highlighted. From absorbed energies, a shock wave analysis, high-speed laser stroboscopy, and thermodynamic data of high-temperature water the enthalpy, temperature, density, pressure, and the reaction time window for the hot water filament could be characterized. The experimental conditions (30 kbar, 1750 K, density ∼1 g/cm3) present during the lifetime of the filament (20−30 ns) were extreme and provided a unique environment for high-temperature water chemistry. For the probe of the reaction products liquid beam desorption mass spectrometry was employed. A decisive feature of the technique is that ionic species, as well as neutral products and intermediates may be detected (neutrals as protonated aggregates) via time-of-flight mass spectrometry without any additional ionization laser. After the explosive disintegration of the superheated beam, high-temperature water reactions are efficiently quenched via expansion and evaporative cooling. For first exploratory experiments for chemistry in ultrahigh-temperature, -pressure and -density water, we have chosen resorcinol as a benchmark system, simple enough and well studied in high-temperature water environments much below 1000 K. Contrary to oxidation reactions usually present under less extreme and dense supercritical conditions, we have observed hydration and little H-atom abstraction during the narrow time window of the experiment. Small amounts of radicals but no ionic intermediates other than simple proton adducts were detected. The experimental findings are discussed in terms of the energetic and dense environment and the small time window for reaction, and they provide firm evidence for additional thermal reaction channels in extreme molecular environments. [ABSTRACT FROM AUTHOR]

An experimental setup for molecular beam scattering from flat liquid sheets has been developed, with the goal of studying reactions at gas-liquid interfaces for volatile liquids. Specifically, a crossed molecular beam instrument that can measure angular and translational energy distributions of scattered products has been adapted for liquid jet scattering. A microfluidic chip is used to create a stable flat liquid sheet inside vacuum from which scattering occurs, and both evaporation and scattering from this sheet are characterized using a rotatable mass spectrometer that can measure product time-of-flight distributions. This article describes the instrument and reports on the first measurements of evaporation of dodecane and Ne from a Ne-doped dodecane flat jet, as well as scattering of Ne from a flat jet of pure dodecane.

Water-insoluble organic UV filters such as 2,2'-methylene-bis-(6-(2 H -benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)-phenol) (MBBT) can be prepared as aqueous dispersions of nanoparticles. The particles consist of the respective UV absorber molecules and show strong UV absorbance. Because there is a certain solubility of such UV absorbers in organic solvents, it is possible to measure the absorbance spectrum in solution also, for instance, in ethanol or dioxane. The UV spectrum of the aqueous dispersion shows a significant bathochromic shift of the long-wavelength band with an additional shoulder. For the understanding of the observed changes of UV-vis spectra of this UV absorber, either dissolved in an organic solvent or dispersed as nanoparticles in water, density functional theory (DFT) calculations were carried out with the respective monomer and aggregates of MBBT molecules in different media. The calculated UV-vis spectra of isolated, that means dissolved, MBBT molecules in ethanol and in dioxane agree well with the experimentally observed ones. The observed changes in the shape and position of experimental UV-vis spectra in aqueous dispersion cannot be explained with the solvent effect alone. It was found that the studied molecules could form stable energetically favorable π-stacked dimers, which show UV-vis spectra in reasonable agreement with those experimentally observed in aqueous dispersion. Such aggregates of MBBT are most likely the reason for the observed bathochromic shift in the UV-vis absorption spectrum. In addition, the mechanism of the photochemical deactivation of the excited MBBT molecules was studied in detail with time-dependent DFT in dioxane and in water. The energetically most favorable pathway for the deactivation of absorbed energy by MBBT occurs through intramolecular enol-keto tautomerization in the first excited singlet state.

We report on a mechanistic investigation regarding the reduction of [Co(III)(dmgH)2(py)(Cl)] (dmg = dimethylglyoxime) by several complementary techniques. The reduction of [Co(III)(dmgH)2(py)(Cl)] was initiated by either electrochemical, photochemical, or pulse radiolytical techniques, and the corresponding products were analyzed by ESI mass spectrometry. In addition, all of the rate constants for each step were determined. We have found solid experimental as well as theoretical evidence for the appearance of a dinuclear complex [Co(II)Co(III)(dmgH)4(py)2(H2O)2](+) to be the final product of reduction, implying the initially reduced form of [Co(III)(dmgH)2(py)(Cl)] undergoes a dimerization with the starting material in solution.

Nanosecond laser flash photolysis employing transient detection of emission and absorption in combination with pulse radiolysis and quantum theory has been employed to shed light into the kinetics, quantum yields, and mechanisms of the deactivation of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))). In contrast to thiophenols (ArSH(S(1))), the results revealed that the decay of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))) is governed by radiationless internal conversion (Φ(IC) = 0.29-0.46; 0.016-0.190) and intersystem crossing (Φ(ISC) = 0.14-0.15; 0.4-0.6), respectively, with pronounced S-H photodissociation (Φ(D) = 0.40-0.55; 0.35-0.40). Fluorescence as a deactivation channel plays a minor role (Φ(F) = 0.001-0.010; 0.010-0.034). Quantum chemical calculations helped in understanding the formation of naphthylthiyl radicals and rationalizing the differences in the efficiency of intersystem crossing of the 1- and 2-thionaphthol systems.

Femtosecond IR pump UV probe spectroscopy was employed in the gas phase to study intramolecular vibrational energy redistribution (IVR) in benzene and five monosubstituted derivatives thereof. After selective excitation of the first overtone of the ring CH-stretch vibration, all molecules showed the same two-step redistribution dynamics characteristic for nonstatistical IVR. The nature of the substituent influences mainly the second, slower IVR component. The presence of an internal rotor does not alter the redistribution rate or pathway compared to that of a monatomic substituent of equal mass. Coupling order model calculations reflect the experimental trends well if the polyatomic substituents are regarded as decoupled from the intra-ring dynamics and modeled as point masses.

Recent work has focused on the damaging effects of free radicals on biological molecules. This study investigates the kinetics of the attack of OH radicals on L-alanine ethyl ester in the gas phase in cold beams of Laval nozzle expansions. Experiments and high-level theory are used to understand the preferred site of attack by the OH radical. Optimizations of L-alanine and L-alanine ethyl ester show that the essential transition state features for hydrogen abstraction off the C(alpha), C(beta), and N are similar. The energetics show that for L-alanine, the C(alpha)-site, C(beta)-site, and N-site transition states are all below the reactants level. For L-alanine ethyl ester, however, the energetics for hydrogen abstraction off the C(alpha) and N are the preferred site of reaction. These findings are supported by the observed negative temperature dependence of the rate constants of OH with alanine ethyl ester in Laval nozzle expansion experiments. More importantly, both the experiments and theory show that L-alanine ethyl ester provides a good model for gas phase studies of the amino acids such as L-alanine.

In the present article a novel approach for rapid product screening of fast reactions in IR-laser-heated liquid microbeams in a vacuum is highlighted. From absorbed energies, a shock wave analysis, high-speed laser stroboscopy, and thermodynamic data of high-temperature water the enthalpy, temperature, density, pressure, and the reaction time window for the hot water filament could be characterized. The experimental conditions (30 kbar, 1750 K, density approximately 1 g/cm3) present during the lifetime of the filament (20-30 ns) were extreme and provided a unique environment for high-temperature water chemistry. For the probe of the reaction products liquid beam desorption mass spectrometry was employed. A decisive feature of the technique is that ionic species, as well as neutral products and intermediates may be detected (neutrals as protonated aggregates) via time-of-flight mass spectrometry without any additional ionization laser. After the explosive disintegration of the superheated beam, high-temperature water reactions are efficiently quenched via expansion and evaporative cooling. For first exploratory experiments for chemistry in ultrahigh-temperature, -pressure and -density water, we have chosen resorcinol as a benchmark system, simple enough and well studied in high-temperature water environments much below 1000 K. Contrary to oxidation reactions usually present under less extreme and dense supercritical conditions, we have observed hydration and little H-atom abstraction during the narrow time window of the experiment. Small amounts of radicals but no ionic intermediates other than simple proton adducts were detected. The experimental findings are discussed in terms of the energetic and dense environment and the small time window for reaction, and they provide firm evidence for additional thermal reaction channels in extreme molecular environments.