Asselin P, Goubet M, Latajka Z, Soulard P, Lewerenz M
LADIR, UMR 7075, Bât F74, Boîte 49, Université Pierre et Marie Curie (Paris VI), 75252 Paris Cedex 05, France.
Phys Chem Chem Phys. 2005 Feb 21;7(4):592-9. doi: 10.1039/b418497a.
Fourier transform infrared spectra of the Vs stretching bands of HF and DF bonded to (CH2)2O have been recorded at 0.5 cm(-1) resolution in a cooled cell and in a supersonic expansion seeded with argon. The analysis of the congested spectra of this type of medium strength hydrogen bonded complexes exploits a combination of controlled temperature effects in the ranges 25-80 K and 200-300 K and a band contour simulation program accounting for homogeneous and inhomogeneous contributions. Significant anharmonic couplings between the donor stretch mode and three of the low frequency intermolecular modes are found to be responsible for the characteristic hot band patterns in the Vs fundamental region of cell spectra. A global analysis of sum and difference combination bands involving Vs provides reliable values of intermolecular frequencies, anharmonic coupling constants and a good estimate of the dissociation energy of the complex which compares favorably with ab initio results. The effective linewidth provides a lower bound for the predissociation lifetime of 1.5 ps for HF and 7 ps for DF containing complexes, respectively. The correlation between effective linewidths and vibrational densities of states for (CH2)2O-HF and -DF underlines the important role of intramolecular vibrational redistribution in the vibrational dynamics of these complexes while the lifetime decrease for HF (or DF) bonded to oxygenated cyclic ethers with respect to sulfured homologues might be explained by the change in the arrangement of the acid relative to the plane of the acceptor subunit.
已在冷却池中以及在以氩气为种子气的超声速膨胀条件下，以0.5厘米⁻¹的分辨率记录了与(CH₂)₂O键合的HF和DF的νs伸缩带的傅里叶变换红外光谱。对这类中等强度氢键复合物的拥挤光谱进行分析时，利用了25 - 80 K和200 - 300 K温度范围内的可控温度效应，以及一个考虑均匀和非均匀贡献的带轮廓模拟程序。发现供体伸缩模式与三个低频分子间模式之间存在显著的非谐耦合，这是导致冷却池光谱νs基频区域特征性热带模式的原因。对涉及νs的和频与差频组合带进行整体分析，可得到可靠的分子间频率、非谐耦合常数，并能很好地估计复合物的解离能，该结果与从头算结果相当。有效线宽分别为含HF和DF的复合物预解离寿命提供了1.5皮秒和7皮秒的下限。(CH₂)₂O - HF和 - DF的有效线宽与态密度之间的相关性强调了分子内振动再分布在这些复合物振动动力学中的重要作用，而与含硫同系物相比，与氧化环醚键合的HF（或DF）寿命降低可能是由于酸相对于受体亚基平面的排列变化所致。
