Photo-tautomerization of acetaldehyde as a photochemical source of formic acid in the troposphere

Organic acids play a key role in the troposphere, contributing to atmospheric aqueous-phase chemistry, aerosol formation, and precipitation acidity. Atmospheric models currently account for less than half the observed, globally averaged formic acid loading. Here we report that acetaldehyde photo-tautomerizes to vinyl alcohol under atmospherically relevant pressures of nitrogen, in the actinic wavelength range, λ = 300–330 nm, with measured quantum yields of 2–25%. Recent theoretical kinetics studies show hydroxyl-initiated oxidation of vinyl alcohol produces formic acid. Adding these pathways to an atmospheric chemistry box model (Master Chemical Mechanism) demonstrates increased formic acid concentrations by a factor of ~1.7 in the polluted troposphere and a factor of ~3 under pristine conditions. Incorporating this mechanism into the GEOS-Chem 3D global chemical transport model reveals an estimated 7% contribution to worldwide formic acid production, with up to 60% of the total modeled formic acid production over oceans arising from photo-tautomerization

First spectroscopic observation of gold(I) butadiynylide: photodetachment velocity map imaging of the AuC4H anion

Published online 29 July 2016The velocity map imaging technique was used in the investigation of gold(i) butadiynylide, AuC4H(-), with images recorded at two excitation wavelengths. The resultant photodetachment spectra show a well defined vibrational progression in the neutral with an energy spacing of 343 ± 3 cm(-1). The adiabatic electron affinity was determined to be 1.775 ± 0.005 eV and assigned to the X(1)Σ(+)←X(2)Σ(+) transition between the anionic and neutral ground states. Franck-Condon simulations performed on density functional theory optimized geometries assisted the assignment of linear geometries to the neutral and anion and the observed vibrational progression to that of the Au-C4H stretch.Bradley R. Visser, Matthew A. Addicoat, Jason R. Gascooke, Warren D. Lawrance, and Gregory F. Meth