The photophysical properties of betanin in aqueous and alcoholic solutions were determined at room temperature using ultrafast UV-vis-NIR transient absorption spectroscopy (λexc = 535 nm). Its S1 → Sn (n > 1) absorption bands appear with maxima at about λ ∼ 450 and 1220 nm. The short betanin S1 state lifetime (6.4 ps in water) is mainly determined by the efficient S1 → S0 radiationless relaxation, probably requiring a strong change in geometry, since the S1 lifetime grows to 27 ps in the more viscous ethylene glycol. The fluorescence quantum yield is very low (Φf ∼ 0.0007 in water), therefore this deactivation path is of minor importance. Other processes, such as S1 → T1 intersystem crossing or photoproduct formation, are virtually absent, since full S0 ← S1 ground state recovery is observed within tens of picoseconds after photoexcitation. The observed fast light-to-heat conversion in the absence of triplet excited state formation supports the idea that betanin is a photoprotector in vivo.

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Fast radiationless S1 → S0 transition in photo-excited betaxanthins is due to conical intersection seam between S1 and S0 surfaces.

The rate of absorption of nitrogen peroxide into water at 25" and 40°C. has been found to be a linear function of the concentration of nitrogen tetroxide in the gas phase and directly proportional to the interfacial partial pressure of the same species.The rate of absorption is independent of gas velocity over a range of Recl from 170 to 350.The results plotted as absorption rate divided by interfacial partial pressure of nitrogen tetroxide show no effect of liquid rate or contact time between gas and liquid over a tenfold range of contact time from 0.03 to 0.3 sec. This indicates that the rate-controlling step during nitrogen dioxide absorption into water is the rate of hydrolysis of nitrogen tetroxide.The absorption rate decreases with increasing temperature from 25' to 40"C., owing to the shift of the equilibrium in the gas phase away from the reacting species nitrogen tetroxide toward nitrogen dioxide and owing to the decreased solubility of nitrogen tetroxide in water. The effect of these factors on absorption more than offsets the effect of the increase in reaction rate and higher diffusivity on absorption at 40°C.The reaction rate constant for the hydrolysis of nitrogen tetroxide has been determined and the solubility of dissolved but unreacted nitrogen tetroxide in equilibrium with gaseous nitrogen tetroxide has been found.Despite the large quantities of nitric acid made by the absorption of nitrogen oxides into water, the kinetics of the reactions involved are not yet fully explained. These reactions are commonly written asThe reaction shown in Equation (3) is the least-understood step of the three.Future efforts to improve the already high efficiency of absorption towers where reaction (3) is carried out will be based on a better understanding of the kinetics of this reaction. To add to the knowledge of this reaction, a study has been made of the kinetics of the absorption and reaction of nitrogen peroxide* with water. Others (4, 6 , LO) who have studied this same problem have shown that nitrogen tetroxide is the reacting species in Equation (3) and that the *Nitrogen peroxide refers to the equilibrium M. M. Wendel is with E.

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Betanin is the best known natural dye belonging to the betacyanin family. In this work, efficient singlet oxygen quenching by betanin in deuterated water with the rate constant 1.20 ± 0.15 × 10(8) M(-1) s(-1) is reported, deduced from the (1)O2 phosphorescence decays measured as a function of betanin concentration. The quenching occurs by a chemical mechanism, as confirmed by the analysis of the transient absorption kinetics at the probe λ ∼ 535 nm, by comparison of the initial triplet signal amplitude of perinaphthenone acting as the (1)O2 photosensitizer with the final bleaching signal of betanin. The main betanin oxidation product is 2-decarboxy-2,3-dehydrobetanin, with its formation observed as the transient absorption signal at λ ∼ 445 nm. LC-MS/MS analysis of the photolyzed solutions supports the product identification as 2-decarboxy-2,3-dehydrobetanin, based on the molecular ion [M](+) observed at m/z 505. Isobetanin also undergoes a similar photooxidation reaction.

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