Experimental observation of molecular-weight growth by the reactions of -benzyne with benzyl radicals.

The chemistry of -benzyne (-CH) is of fundamental importance due to its role as an essential molecular building block in molecular-weight growth reactions. Here, we report on an experimental investigation of the reaction of -CH with benzyl (CH) radicals in a well-controlled flash pyrolysis experiment using a resistively heated SiC microtubular reactor at temperatures of 800-1600 K and pressures near 30  torr. To this end, the reactants -CH and CH were pyrolytically generated from 1,2-diiodobenzene and benzyl bromide, respectively.

Gas-phase preparation of azulene (CH) and naphthalene (CH) the reaction of the resonantly stabilized fulvenallenyl and propargyl radicals.

Synthetic routes to the 10π Hückel aromatic azulene (CH) molecule, the simplest polycyclic aromatic hydrocarbon carrying an adjacent five- and seven-membered ring, have been of fundamental importance due to the role of azulene - a structural isomer of naphthalene - as an essential molecular building block of saddle-shaped carbonaceous nanostructures such as curved nanographenes and nanoribbons. Here, we report on the very first gas phase preparation of azulene by probing the gas-phase reaction between two resonantly stabilized radicals, fulvenallenyl and propargyl , in a molecular beam through isomer-resolved vacuum ultraviolet photoionization mass spectrometry. Augmented by electronic structure calculations, the novel Fulvenallenyl Addition Cyclization Aromatization (FACA) reaction mechanism affords a versatile concept for introducing the azulene moiety into polycyclic aromatic systems thus facilitating an understanding of barrierless molecular mass growth processes of saddle-shaped aromatics and eventually carbonaceous nanoparticles (soot, interstellar grains) in our universe.

Quantification of Key Peroxy and Hydroperoxide Intermediates in the Low-Temperature Oxidation of Dimethyl Ether.

Dimethyl ether (DME) oxidation is a model chemical system with a small number of prototypical reaction intermediates that also has practical importance for low-carbon transportation. Although it has been studied experimentally and theoretically, ambiguity remains in the relative importance of competing DME oxidation pathways in the low-temperature autoignition regime. To focus on the primary reactions in DME autoignition, we measured the time-resolved concentration of five intermediates, CHOCHOO (ROO), OOCHOCHOOH (OOQOOH), HOOCHOCHO (hydroperoxymethyl formate, HPMF), CHO, and CHOCHO (methyl formate, MF), from photolytically initiated experiments.

Experimental Observation of Hydrocarbon Growth by Resonance-Stabilized Radical-Radical Chain Reaction.

Rapid molecular-weight growth of hydrocarbons occurs in flames, in industrial synthesis, and potentially in cold astrochemical environments. A variety of high- and low-temperature chemical mechanisms have been proposed and confirmed, but more facile pathways may be needed to explain observations. We provide laboratory confirmation in a controlled pyrolysis environment of a recently proposed mechanism, radical-radical chain reactions of resonance-stabilized species.

Generation of extreme-ultraviolet beams with time-varying orbital angular momentum.

Light fields carrying orbital angular momentum (OAM) provide powerful capabilities for applications in optical communications, microscopy, quantum optics, and microparticle manipulation. We introduce a property of light beams, manifested as a temporal OAM variation along a pulse: the self-torque of light. Although self-torque is found in diverse physical systems (i.

Ultrafast 25-fs relaxation in highly excited states of methyl azide mediated by strong nonadiabatic coupling.

Highly excited electronic states are challenging to explore experimentally and theoretically-due to the large density of states and the fact that small structural changes lead to large changes in electronic character with associated strong nonadiabatic dynamics. They can play a key role in astrophysical and ionospheric chemistry, as well as the detonation chemistry of high-energy density materials. Here, we implement ultrafast vacuum-UV (VUV)-driven electron-ion coincidence imaging spectroscopy to directly probe the reaction pathways of highly excited states of energetic molecules-in this case, methyl azide.

A new electron-ion coincidence 3D momentum-imaging method and its application in probing strong field dynamics of 2-phenylethyl-N, N-dimethylamine.

We report the development of a new three-dimensional (3D) momentum-imaging setup based on conventional velocity map imaging to achieve the coincidence measurement of photoelectrons and photo-ions. This setup uses only one imaging detector (microchannel plates (MCP)/phosphor screen) but the voltages on electrodes are pulsed to push both electrons and ions toward the same detector. The ion-electron coincidence is achieved using two cameras to capture images of ions and electrons separately.

Tabletop Femtosecond VUV Photoionization and PEPICO Detection of Microreactor Pyrolysis Products.

We report the combination of tabletop vacuum ultraviolet photoionization with photoion-photoelectron coincidence spectroscopy for sensitive, isomer-specific detection of nascent products from a pyrolysis microreactor. Results on several molecules demonstrate two essential capabilities that are very straightforward to implement: the ability to differentiate isomers and the ability to distinguish thermal products from dissociative ionization. Here, vacuum ultraviolet light is derived from a commercial tabletop femtosecond laser system, allowing data to be collected at 10 kHz; this high repetition rate is critical for coincidence techniques.

Uncovering Highly-Excited State Mixing in Acetone Using Ultrafast VUV Pulses and Coincidence Imaging Techniques.

Understanding the ultrafast dynamics of highly excited electronic states of small molecules is critical for a better understanding of atmospheric and astrophysical processes, as well as for designing coherent control strategies for manipulating chemical dynamics. In highly excited states, nonadiabatic coupling, electron-electron interactions, and the high density of states govern dynamics. However, these states are computationally and experimentally challenging to access.

Ethanol-enhanced cytotoxicity of alkylating agents.

Background: Although ethanol itself is not genotoxic, chronic alcohol consumption increases the risk of neoplastic disease. The mechanism by which ethanol exerts a cocarcinogenic effect is not well established, and the aim of this study was to determine whether exposure to ethanol increased the cytotoxicity of known carcinogens.

Methods: To assess cell survival, the ability of Chinese hamster A10 cells, which express alcohol dehydrogenase, to form colonies was determined after exposure to ethanol and other substances, including both genotoxicants and non-DNA-reactive cytotoxic agents.