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Uptake of short-chain alcohols by sulfuric acid solutions using Raman and vibrational sum frequency spectroscopies, and atmospheric implications
The organization of two longer but still slightly miscible alcohols, 1-butanol and 1-hexanol, at the air-liquid interface of aqueous, aqueous ammonium bisulfate, and sulfuric acid solutions was investigated using vibrational broad bandwidth sum frequency generation spectroscopy. There is spectroscopic evidence supporting the formation of centrosymmetric structures at the surface of pure butanol and pure hexanol. At aqueous, ammonium bisulfate, and at most sulfuric acid solution surfaces, butanol molecules organize in all-trans conformations. This suggests that butanol self-aggregates. The 0.052 M butanol in 59.5 wt% sulfuric acid solution is different from the other butanol solution spectra; that is, the surface butanol molecules possess a significant number of gauche defects. Relative to surface butanol, surface hexanol chains are significantly more disordered at the surface of their respective solutions. The surface spectra for butanol and hexanol also show evidence for salting out from the ammonium bisulfate solutions.
- "The organization of two longer but still slightly miscible alcohols, 1-butanol and 1-hexanol, at the air-liquid interface of aqueous, aqueous ammonium bisulfate, and sulfuric acid solutions was investigated using vibrational broad bandwidth sum frequency generation spectroscopy. There is spectroscopic evidence supporting the formation of centrosymmetric structures at the surface of pure butanol and pure hexanol. At aqueous, ammonium bisulfate, and at most sulfuric acid solution surfaces, butanol molecules organize in all-trans conformations. This suggests that butanol self-aggregates. The 0.052 M butanol in 59.5 wt% sulfuric acid solution is different from the other butanol solution spectra; that is, the surface butanol molecules possess a significant number of gauche defects. Relative to surface butanol, surface hexanol chains are significantly more disordered at the surface of their respective solutions. The surface spectra for butanol and hexanol also show evidence for salting out from the ammonium bisulfate solutions."@en
- "As the concentration of SA increases from 0 - 96.5 wt%, the SFG spectra shift from that of methanol to that of methyl hydrogen sulfate. The surface is saturated with a mixture of the three methyl compounds after 15 minutes, although the relative amounts of MeOH, MeOH₂, and MHS vary with SA concentration. The uptake of MeOH, MeOH₂, and MHS into the solutions was also observed, although this occurred on a much longer timescale. This suggests that uptake of methanol by sulfuric acid solutions is diffusion-limited."@en
- "The diffusion coefficients for methanol into 0 - 96.5 wt% sulfuric acid solutions were measured by passing MeOH vapor in N₂ over the SA solutions and monitoring the uptake using Raman spectroscopy. The value obtained for methanol into water, D = (0.7 ± 0.2) x 10⁻⁵ cm²/s, is in agreement with values found in the literature. The values of D in 39.2 to 96.5 wt% SA range from (1 - 2.7) x 10⁻⁶ cm²/s with the maximum value of D occurring for the 59.5 wt% SA solution. This may be due to the speciation of MeOH in the SA solutions or to speciation of the SA solutions."@en
- "Abstract: The uptake and reaction of methanol (MeOH) at the air-liquid interface of 0 to 96.5 wt% sulfuric acid (SA) solutions has been observed directly using vibrational sum frequency generation spectroscopy (VSFG) and Raman spectroscopy. Evidence for the formation of methyl hydrogen sulfate (MHS) was obtained by the presence of a new peak in the 800 cm⁻¹ region, not present in either the neat methanol or concentrated sulfuric acid spectra. This peak is attributed to the singly bonded OSO symmetric stretch of MHS. The maximum yield of MHS with a large SA excess (7 SA : 1 methanol) is shown to be (95 ± 5) % at (15 ± 2) °C. No evidence was found to suggest formation of dimethyl sulfate."@en
- "Uptake of short-chain alcohols by sulfuric acid solutions using Raman and vibrational sum frequency spectroscopies, and atmospheric implications"@en