Influence of Intramolecular Hydrogen Bonding on OH-Stretching Overtone Intensities and Band Positions in Peroxyacetic Acid

Abstract

Vapor phase absorption spectra and integrated band intensities of the OH stretching fundamental as well as first and second overtones (2ν(OH) and 3ν(OH)) in peroxyacetic acid (PAA) have been measured using a combination of FT-IR and photoacoustic spectroscopy. In addition, ab initio calculations have been carried out to examine the low energy stable conformers of the molecule. Spectral assignment of the primary features appearing in the region of the 2ν(OH) and 3ν(OH) overtone bands are made with the aid of isotopic substitution and anharmonic vibrational frequency calculations carried out at the MP2/aug-cc-pVDZ level. Apart from features associated with the zeroth-order OH stretch, the overtone spectra are dominated by features assigned to combination bands composed of the respective OH stretching overtone and vibrations involving the collective motion of several atoms in the molecule resulting from excitation of the internal hydrogen bonding coordinate. Integrated absorption cross section measurements reveal that internal hydrogen bonding, the strength of which is estimated to be ∼20 kJ/mol in PAA, does not result in a enhanced oscillator strength for the OH stretching fundamental of the molecule, as is often expected for hydrogen bonded systems, but does cause a precipitous drop in the oscillator strength of its 2ν(OH) and 3ν(OH) overtone bands, reducing them, respectively, by a factor of 165 and 7020 relative to the OH stretching fundamental.

UV Photochemistry of Peroxyformic Acid (HC(O)OOH): An Experimental and Computational Study Investigating 355 nm Photolysis

“…By contrast, our computational results predict that there will be significant OH rotational excitation upon UV excitation of PFA at shorter wavelengths corresponding to excitations to the higher energy 2 1 A″ excited state. The present results also suggest an analogous behavior with respect to OH fragment rotation resulting from the photodissociation of peroxyacetic acid, which is a related molecule exhibiting internal hydrogen bonding. , …”

“…The present results also suggest an analogous behavior with respect to OH fragment rotation resulting from the photodissociation of peroxyacetic acid, which is a related molecule exhibiting internal hydrogen bonding. 24,60 V. CONCLUSION Absorption of 355 nm light by PFA leads to excitation to the repulsive 1…”

Intramolecular hydrogen-bonding effects on O H stretch overtone excitation for fluorinated hydroperoxides

“…Compared to other molecules with intramolecular hydrogen bonding, the O-H stretch red shifts observed here are at the low end of those reported in the literature, which range from ~20 to over 100 cm -1 [38][39][40][41][42][43]. Red shifts for fluorinated [37] and hydrogen-bonded [30,37,38,[40][41][42][43] species become even more pronounced at higher overtones.…”

“…There is also a drop in relative cross section, compared to the fundamental's, as the number of fluorines on the hydroperoxide increases (Table 2). Hydrogen bonding is known to increase the relative drop in overtone intensity even further.. Sinha and co-workers [40,41] have documented more dramatic drops in overtone intensity relative to the fundamental and attributed them to intramolecular hydrogen bonding in peroxyformic and peroxyacetic acids.…”

Red-light initiated atmospheric reactions of vibrationally excited molecules

“…In pyruvic, glyoxylic, peroxyformic and peroxyacetic acids reaction is initiated by excitation of the 3rd and 4th OH stretching overtone, initiated by hydrogen atom chattering between the two oxygen atoms to drive the overall formation of a reactive intermediate on subpicosecond timescales. 88,113,130,183 Fast unimolecular reactions like those described above may lead to high-energy products in the real environment by competing with energy dissipation over other small barriers processes. Understanding the dynamics of the competition between these processes is necessary for predictions of the chemical outcome of light initiated reactions under real environmental conditions.…”