UPMC Univ. Paris 06, UMR 7075, Laboratoire de Dynamique, Interactions et Réactivité (LADIR), F-75005, Paris, France.
Phys Chem Chem Phys. 2011 Aug 21;13(31):14202-14. doi: 10.1039/c1cp20668k. Epub 2011 Jul 14.
The coexistence of axial and equatorial hydrogen-bonded conformers of 1 : 1 (CH(2))(3)S-HF (and -DF) has been observed in the same adiabatic expansion of a supersonic jet seeded with argon and in a static absorption cell at room temperature. High level calculations computed the axial conformer to be the most stable one with a small energy difference with respect to the equatorial one, in full agreement with previous microwave experiments. On the grounds of band contour simulations of FTIR spectra and ab initio energetic and anharmonic vibrational calculations, two pairs of ν(s) HF donor stretching bands, observed in a series of jet-FTIR spectra at 3457.9 and 3480.5 cm(-1) have been respectively assigned to the axial and equatorial forms of the 1 : 1 complex. In the jet-FTIR spectra series with HF, the assignment of an additional broad band (about 200 cm(-1) higher in frequency with respect to ν(s)) to a 1 : 2 complex has been supported by theoretical investigations. Experimental detection of both axial and equatorial forms of a cyclic trimer has been confirmed by calculated energetic and vibrational properties. The nature of hydrogen bonding has been examined within topological frameworks. The energetic partitioning within the 1 : 1 dimers has been elucidated with SAPT techniques. Interestingly, the interconversion pathway between two 1 : 1 structures has been explored and it was seen that the formation of the 1 : 1 complex affects the interconversion barrier on the ring puckering motion. The band contour analysis of gas phase FTIR experiments provided a consistent set of vibrational frequencies and anharmonic coupling constants, in good agreement with ab initio anharmonic vibrational calculations. Finally, from a series of cell-FTIR spectra recorded at different partial pressures of (CH(2))(3)S and HF monomers, the absorption signal of the 1 : 1 complex could be isolated which enabled to estimate the equilibrium constant K(p) = 0.023 at 298 K for the dimerization.
在同一亚音速喷射中，观察到了 1：1(CH(2))(3)S-HF（和-DF）的轴向和赤道氢键构象的共存，喷射中种子氩气，在室温下的静态吸收池中。高水平的计算表明，轴向构象是最稳定的，与赤道构象相比，其能量差异很小，这与之前的微波实验完全一致。基于 FTIR 光谱的带轮廓模拟和从头算能量和非谐振动计算，在一系列喷射-FTIR 光谱中观察到的两个 ν(s)HF 供体伸缩带，在 3457.9 和 3480.5 cm(-1)，分别被分配给 1：1 络合物的轴向和赤道形式。在 HF 的喷射-FTIR 光谱系列中，通过理论研究支持了对另一个宽带（频率比 ν(s)高约 200 cm(-1)）分配给 1：2 络合物的分配。通过计算的能量和振动性质，证实了环状三聚体的轴向和赤道形式的实验检测。在拓扑框架内检查了氢键的性质。使用 SAPT 技术阐明了 1：1 二聚体中的能量分配。有趣的是，探索了两种 1：1 结构之间的互变途径，并且发现 1：1 络合物的形成影响了环扭转运动的互变势垒。气相 FTIR 实验的带轮廓分析提供了一组一致的振动频率和非谐耦合常数，与从头算非谐振动计算吻合良好。最后，从不同的（CH(2))(3)S 和 HF 单体分压下记录的一系列细胞-FTIR 光谱中，可以分离出 1：1 络合物的吸收信号，从而可以估计 298 K 时二聚体的平衡常数 K(p)=0.023。
