While calibrating a new scientific apparatus at the ALS, researchers discovered that ultraviolet light can break up sulfur dioxide (SO2) in a new way, with molecular oxygen (O2) as an unexpected product. The discovery sheds light on Earth’s Great Oxygenation Event 2.4 billion years ago, when atmospheric oxygen levels first began to rise. Read more »
ALS Work Using Mass Spectrometry
Mass spectrometry is an experimental technique used for identifying molecules. Neutral molecules are ionized, and the charged species are sorted by magnetic and/or electric fields according to mass. A mass spectrum is a plot of the ion signal intensity as a function of mass-to-charge ratio (m/z). The atoms or molecules in a sample can be identified by correlating the mass spectrum with known molecular masses or characteristic fragmentation patterns.
The Identity and Chemistry of C7H7 Radicals Observed during Soot Formation
Recent work suggests that resonance-stabilized radicals may participate in chain reactions that lead to soot-particle formation, but their identities and chemistry are poorly understood. C7H7 is often observed in aerosol mass spectra and is generally assumed to be benzyl, the most thermodynamically stable C7H7 isomer. It has now been shown that the identities of these isomers are far more varied, and their chemistry is far more complex, than previously appreciated. Read more »
SO2 Photodissociation at 193 nm Directly Forms S(3P) + O2(3Σg–): Implications for the Archean Atmosphere on Earth
Sulfur isotope patterns in ancient rock layers inform our understanding of Earth’s Archean atmosphere. Before the Great Oxygenation Event (~2.4 billion years ago), hard ultraviolet light penetrated into the Earth’s surface, photodissociating sulfur dioxide directly to S + O2. This new product channel may help resolve discrepancies in the Earth’s evolutionary history. Read more »
Gas-phase synthesis of racemic helicenes and their potential role in the enantiomeric enrichment of sugars and amino acids in meteorites
Molecular-beam experiments with isomer-selective photoionization via a targeted, vinylacetylene-mediated gas-phase reaction of aromatic helicenyl radicals coupled with electronic structure calculations and astrochemical modeling reveal an elegant synthetic route to racemic helicenes – ortho-fused polycyclic aromatic hydrocarbons (PAHs), in which benzene building blocks form helically-shaped molecules. Read more »
Dramatic Conformer-Dependent Reactivity of the Acetaldehyde Oxide Criegee Intermediate with Dimethylamine Via a 1,2-Insertion Mechanism
Acetaldehyde-oxide (CH3CHOO) is an atmospherically pertinent reactive intermediate that exists in syn (right) and anti (left) conformational forms. Experiment and theory reveal that the reaction of anti with dimethylamine is several orders of magnitude faster than that of syn with dimethylamine, despite both reactions being energetically downhill. Read more »
Chemical (and Strategic) Transformations at Beamline 9.0
The Chemical Dynamics beamline, used for gas-phase vacuum ultraviolet (VUV) experiments, was one of the first beamlines built at the ALS. Since then, the program has undergone several strategic transformations, enabling the study of complexity in clusters, aerosols, and nanoparticles using both VUV and soft x-ray radiation. Read more »
Key to Cleaner Combustion? Look to the Stars
Researchers made the first real-time, lab-based measurement of free radicals reacting under cosmic conditions, prompting elementary carbon and hydrogen atoms to coalesce into primal benzene rings. The findings are key to understanding how the universe evolved with the growth of carbon compounds and could also help the car industry make cleaner combustion engines. Read more »
Gas-phase synthesis of corannulene—a molecular building block of fullerenes
Fullerenes have been implicated to play a key role in the astrochemical evolution of the interstellar medium. However, the formation mechanism of even their simplest molecular building block—corannulene—has remained elusive. Here we demonstrate that corannulene can be synthesized in the gas phase through reactions mimicking conditions in carbon-rich circumstellar envelopes. Read more »
Extreme Low-Temperature Combustion Chemistry: Ozone-Initiated Oxidation of Methyl Hexanoate
The accelerating effect of ozone on the oxidation of methyl hexanoate was probed with time-of-flight mass spectrometry. A new oxidation regime was observed at temperatures below the well-known low-temperature chemistry regime. The results indicate that the chemistry in this regime is initiated by thermal ozone dissociation and subsequent H abstraction from methyl hexanoate by O atoms. Read more »
Criegee Intermediates Play Unexpected Role in Cell Chemistry
Researchers employed mass spectrometry to illuminate lipid nanodroplets under ultraviolet light. The results unexpectedly showed that hydroxyl radicals cause damage to cells via the formation of Criegee intermediates: molecules first proposed in 1975 to explain how pollutants react with the ozone layer in our atmosphere. Read more »