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Uptake of short-chain alcohols by sulfuric acid solutions using raman and vibrational sum frequency spectroscopies, and atmospheric implications

Van Loon, Lisa Lauralene

Abstract Details

2007, Doctor of Philosophy, Ohio State University, Chemistry.

The uptake and reaction of methanol at the air-liquid interface of 0-96.5 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 is shown to be (95±5)% at –(15±2)°C. No evidence was found to suggest formation of dimethyl sulfate.

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. Uptake occurred on a much longer timescale, suggesting that uptake of methanol by sulfuric acid solutions is diffusion-limited.

The diffusion coefficients for methanol into 0–96.5 wt% sulfuric acid solutions were measured by passing MeOH vapor in N2over the SA solutions and monitoring the uptake using Raman spectroscopy. The value obtained for methanol into water, D = (0.7±0.2) x 10-5cm2/s, is in agreement with values found in the literature. The values of D in 39.2-96.5 wt% SA range from (1–2.7) x 10-6cm2/s with the maximum value 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.

The organization of 1-butanol and 1-hexanol, at air-liquid interfaces was investigated using VSFG. There is evidence for centrosymmetric structures at the surface of pure butanol and hexanol. At most solution surfaces, butanol molecules organize in all-trans conformations. In contrast, the spectrum of 0.052 M butanol in 59.5 wt% sulfuric acid solution possesses a significant number of gauche defects. Relative to surface butanol, surface hexanol chains are significantly more disordered at the surface of the solutions.

Heather Allen (Advisor)
130 p.

Recommended Citations

Citations

  • Van Loon, L. L. (2007). Uptake of short-chain alcohols by sulfuric acid solutions using raman and vibrational sum frequency spectroscopies, and atmospheric implications [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1174323601

    APA Style (7th edition)

  • Van Loon, Lisa. Uptake of short-chain alcohols by sulfuric acid solutions using raman and vibrational sum frequency spectroscopies, and atmospheric implications. 2007. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1174323601.

    MLA Style (8th edition)

  • Van Loon, Lisa. "Uptake of short-chain alcohols by sulfuric acid solutions using raman and vibrational sum frequency spectroscopies, and atmospheric implications." Doctoral dissertation, Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1174323601

    Chicago Manual of Style (17th edition)