Department of Chemistry and Biochemistry, University of California, San Diego La Jolla, California 92093-0314, United States.
J Phys Chem A. 2012 Jun 21;116(24):5784-95. doi: 10.1021/jp206637t. Epub 2011 Oct 11.
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.
已使用傅里叶变换红外光谱和光声光谱联用技术测量了过氧乙酸（PAA）中 OH 伸缩基频以及第一和第二泛频（2ν（OH）和 3ν（OH））的气相吸收光谱和积分带强度。此外，还进行了从头算计算以研究分子的低能稳定构象。在 MP2/aug-cc-pVDZ 水平上进行的同位素取代和非谐振动频率计算有助于对 2ν（OH）和 3ν（OH）泛频带区域中出现的主要特征进行光谱分配。除了与零阶 OH 伸缩相关的特征外，泛频光谱主要由组合带特征主导，这些组合带由各自的 OH 伸缩泛频和涉及分子中几个原子的集体运动的振动组成，这是由内部氢键坐标激发引起的。积分吸收截面测量表明，内部氢键不会导致分子的 OH 伸缩基频的振子强度增强，如通常预期的氢键体系那样，其强度估计在 PAA 中约为 20 kJ/mol，但确实导致其 2ν（OH）和 3ν（OH）泛频带的振子强度急剧下降，相对于 OH 伸缩基频，它们分别降低了 165 和 7020 倍。
