Bodi Andras, Kercher James P, Baer Tomas, Sztáray Bálint
Department of General and Inorganic Chemistry, Eötvös Lorand University, Budapest, Hungary.
J Phys Chem B. 2005 May 5;109(17):8393-9. doi: 10.1021/jp046353s.
Energy selected trimethyl phosphine ions were prepared by threshold photoelectron photoion coincidence (TPEPICO) spectroscopy. This ion dissociates via H, CH(3), and CH(4) loss, the latter two involving hydrogen transfer steps. The ion time-of-flight distribution and the breakdown diagram are analyzed in terms of the statistical RRKM theory, which includes tunneling. Ab initio and DFT calculations provide the vibrational frequencies required for the RRKM modeling. CH(3) loss could produce both the P(CH(3))(2)(+) by a simple bond dissociation step, and the more stable HP(CH(2))CH(3)(+) ion by a hydrogen transfer step. Quantum chemical calculations are extensively used to uncover the reaction scheme, and they strongly suggest that the latter product is exclusively formed via an isomerization step in the energy range of the experiment. The data analysis, which includes modeling with the trimethyl phosphine thermal energy distribution, provides accurate onset energies for both H (E(0K) = 1024.1 +/- 3.5 kJ/mol) and CH(3) (E(0K) = 1024.8 +/- 3.5 kJ/mol) loss reactions. From this analysis, we conclude that the Delta(f)H(298K) degrees [HP(CH(2))(CH(3))(+)] = 783 +/- 8 kJ/mol and Delta(f)H(298K) degrees [P(CH(2))(CH(3))(2)(+)] = 711 +/- 8 kJ/mol.
通过阈值光电子光离子符合（TPEPICO）光谱制备了能量选择的三甲基膦离子。该离子通过损失H、CH₃和CH₄进行解离，后两者涉及氢转移步骤。根据包括隧穿效应的统计RRKM理论对离子飞行时间分布和分解图进行了分析。从头算和密度泛函理论计算提供了RRKM建模所需的振动频率。CH₃损失既可以通过简单的键解离步骤产生P(CH₃)₂⁺，也可以通过氢转移步骤产生更稳定的HP(CH₂)CH₃⁺离子。量子化学计算被广泛用于揭示反应机理，并且强烈表明在实验能量范围内，后一种产物仅通过异构化步骤形成。数据分析包括用三甲基膦热能分布进行建模，为H（E(0K)=1024.1±3.5kJ/mol）和CH₃（E(0K)=1024.8±3.5kJ/mol）损失反应提供了准确的起始能量。通过该分析，我们得出ΔfH(298K)°[HP(CH₂)(CH₃)⁺]=783±8kJ/mol和ΔfH(298K)°[P(CH₂)(CH₃)₂⁺]=711±8kJ/mol。
