Kercher James P, Gengeliczki Zsolt, Sztáray Bálint, Baer Tomas
The Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290, USA.
J Phys Chem A. 2007 Jan 11;111(1):16-26. doi: 10.1021/jp0652392.
The sequential ethene (C2H4) loss channels of energy-selected ethylphosphine ions have been studied using threshold photoelectron photoion coincidence (TPEPICO) spectroscopy in which ion time-of-flight (TOF) distributions are recorded as a function of the photon energy. The ion TOF distributions and breakdown diagrams have been modeled in terms of the statistical RRKM theory for unimolecular reactions, providing 0 K dissociation onsets, E0, for the ethene loss channels. Three RRKM curves were used to model the five measurements, since two of the reactions differ only by the internal energy of the parent ion. This series of dissociations provides a detailed check of the calculation of the product energy distribution for sequential reactions. From the determined E0's, the heats of formation of several ethylphosphine neutrals and ions have been determined: Delta(f)H degrees 298K[P(C(2)H(5))3] = -152.7 +/- 2.8 kJ/mol, Delta(f)H degrees 298K[P(C(2)H(5))3+] = 571.6 +/- 4.0 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2] = -89.6 +/- 2.1 kJ/mol, Delta(f)H degrees 298K[HP(C(2)H(5))2+] = 669.9 +/- 2.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)] = -36.5 +/- 1.5 kJ/mol, Delta(f)H degrees 298K[H(2)PC(2)H(5)+] = 784.0 +/- 1.9 kJ/mol. These values have been supported by G2 and G3 calculations using isodesmic reactions. Coupled cluster calculations have been used to show that the C2H4 loss channel, which involves a hydrogen transfer step, proceeds without a reverse energy barrier.
利用阈值光电子光离子符合（TPEPICO）光谱研究了能量选择的乙基膦离子的顺序乙烯（C2H4）损失通道，其中离子飞行时间（TOF）分布作为光子能量的函数被记录下来。离子TOF分布和分解图已根据单分子反应的统计RRKM理论进行建模，给出了乙烯损失通道的0K解离起始点E0。由于其中两个反应仅在母离子的内能上有所不同，因此使用三条RRKM曲线对五次测量进行建模。这一系列解离为顺序反应产物能量分布的计算提供了详细检验。根据确定的E0，确定了几种乙基膦中性分子和离子的生成热：ΔfH°298K[P(C2H5)3] = -152.7±2.8 kJ/mol，ΔfH°298K[P(C2H5)3+] = 571.6±4.0 kJ/mol，ΔfH°298K[HP(C2H5)2] = -89.6±2.1 kJ/mol，ΔfH°298K[HP(C2H5)2+] = 669.9±2.5 kJ/mol，ΔfH°298K[H2PC2H5] = -36.5±1.5 kJ/mol，ΔfH°298K[H2PC2H5+] = 784.0±1.9 kJ/mol。这些值得到了使用等键反应的G2和G3计算的支持。耦合簇计算已用于表明涉及氢转移步骤的C2H4损失通道在没有反向能垒的情况下进行。
