Recent studies have shown that pyruvic acid can produce higher-molecular-weight compounds upon irradiation in the aqueous phase. These compounds can contribute to the formation of secondary organic aerosols. There have been several previous studies on the effect of ionic strength on the photochemistry of pyruvic acid; however, few of them investigated the effects of marine relevant salts such as NaCl and CaCl 2 . In this study, we examine the effect of NaCl and CaCl 2 , namely, containing the coordinating cations Na + and Ca 2+ , on the speciation, absorption properties, and photoreactivity of pyruvic acid in aqueous solutions of varying pH. NMR shows that both Ca 2+ and Na + further deprotonate pyruvic acid and decrease the diol to ketone ratio of pyruvic acid than in pure water at the same pH, especially at more acidic pH (pH less than 4). The absorption spectrum shows a strong red shift in the peak maxima for the n → π* transition of pyruvic acid in NaCl/CaCl 2 solutions. This dependence is much more pronounced for divalent cations (Ca 2+ ) compared to monovalent cations (Na + ). Vertical excitation energy calculations of the anionic ketone form of pyruvic acid confirm the same red shift on the n → π* transition peak in the presence of Ca 2+ . In addition, the presence of NaCl/CaCl 2 suppresses the photolysis rate of pyruvic acid, which could be due to the deprotonation of pyruvic acid by the cations and the lower photochemical reactivity for pyruvate, the deprotonated form.

The visible absorption bands of the phenylperoxy radical in the gas phase have been investigated using cavity ring-down spectroscopy. Jet-cooling was used to reduce the spectral congestion. Structured spectra spanning the range from 17 500 to 19 000 cm–1 are reported for the first time. Analyses of these data have been guided by the results from time-dependent density functional calculations. The observed spectrum was found to be dominated by the bands of the B̃2A″–X̃2A″ transition. An analysis of the rotational contour for the origin band yielded a homogeneous line width of 2.2 cm–1, corresponding to a decay rate of 4.1 × 1011 s–1. The results provide a rationale for the lack of structure in room temperature spectra that have been previously attributed to phenylperoxy. They also indicate that the lower energy region of the spectrum may show resolvable structure at room temperature. If so, this would provide a more definitive signature for monitoring phenylperoxy in kinetic measurements.

Determination of HNO3 coverage on silica provides insight into different HNO3 surface photolysis rates without and with humidity.

The electronic spectrum of CaO has been recorded for the 29800-33150 cm -1 energy range. Jet cooling was used to obtain relatively uncongested spectra. Rotationally resolved bands have been assigned to the C 1  + -X 1  + and F 1  -X transitions. These data extend the range of vibronic levels characterized for the upper states. Three additional vibronic states were observed as a short progression. One of these levels, which are of 0 + symmetry, interacts strongly with the C 1  + , v=7 level. Possible assignments for the perturbing state are considered.