Dissociative photoionization of chromium hexacarbonyl: A round-trip ticket to non-statisticality and a detective story in thermochemistry
Dissociative photoionization of chromium hexacarbonyl: A round-trip ticket to non-statisticality and a detective story in thermochemistry
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DOI：
10.1016/j.ijms.2018.12.010
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发表时间：
2019-04-01
影响因子：
1.8
通讯作者：
Sztaray, Balint
中科院分区：
文献类型：
--
作者：
Voronova, Krisztina;Torma, Krisztian G.;Sztaray, Balint
在瑞士光源的真空紫外光束线上，用成像光电子光离子符合谱（iPEPICO）研究了内能选择的六羰基铬离子Cr（CO）（6）（+）的碎裂过程.在9.3 - 21.5 eV的光子能量范围内，Cr（CO）（6）（+）通过六个连续的羰基配体损失解离。碎片离子丰度分数，绘制在击穿图中，沿着与飞行时间质谱的前三个亚稳态CO损失通道使用统计方法建模。在12和16 eV之间，统计模型高估了碎片化的程度，这可以通过母离子Cr（CO）（6）（+）的排斥电子态上的脉冲CO损失中增强的动能释放来解释，如TD-DFT计算所证实的。这是第一个报道的例子嵌入式非统计单分子解离制度，括号内的统计制度在低和高能量。用统计模型计算了Cr（CO）（n）（+）（n = 0-5）的零K出现能. Cr（CO）（5）（+）的出现能和文献中的CO-Cr（CO）（5）（+）键离解能产生的绝热Cr（CO）（6）（+）电离能为8.195 +/-0.120 eV，与光电子能谱测量无关。Cr+的0 K表观能比基于文献生成焓的预测高61 kJ mol（-1），我们认为这很可能是由于Cr（CO）（6）的生成焓中的误差，并提出修正的Δ H-f [Cr（CO）（6），g]=-972.1 +/-4.1和-968.9 +/-4.1 kJ mol（-1），在0和298 K下，以及基于已知升华焓，对于结晶状态，Δ H-f（298 K）[Cr（CO）（6），c]=-1040.6 +/-4.2 kJ mol（-1）。本文还报道了[（CO）（n）Cr-CO]（+）（n = 0 - 5）中Cr-CO键的离解能和羰基铬离子系列的形成过程。(C)2018由Elsevier B.V.出版
The fragmentation processes of internal energy selected chromium hexacarbonyl cations, Cr(CO)(6)(+), were investigated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy at the VUV beamline of the Swiss Light Source. In the 9.3-21.5 eV photon energy range, Cr(CO)(6)(+) dissociates by six sequential carbonyl ligand losses. The fragment ion fractional abundances, plotted in the breakdown diagram, along with the time-of-flight mass spectra for the first three metastable CO-loss channels were modeled using a statistical approach. Between 12 and 16 eV, the statistical model overestimates the degree of fragmentation, which is explained by enhanced kinetic energy release in impulsive CO loss on repulsive electronic states of the parent ion Cr(CO)(6)(+), as confirmed by TD-DFT calculations. This is the first reported example for an embedded non-statistical unimolecular dissociation regime, bracketed by statistical regimes at low and at high energies. The statistical model was employed to derive 0 K appearance energies for Cr( CO)(n)(+) (n= 0-5). The Cr(CO)(5)(+) appearance energy and the literature CO-Cr(CO)(5)(+) bond dissociation energy yield an adiabatic Cr(CO)(6)(+) ionization energy of 8.195 +/- 0.120 eV, independent of photoelectron spectroscopy measurements. The 0 K appearance energy of Cr+ is 61 kJ mol(-1) higher than predicted based on literature enthalpies of formation, which we suggest is most likely due to an error in the enthalpy of formation of Cr(CO)(6), and propose a revised Delta H-f[Cr(CO)(6), g] = -972.1 +/- 4.1 and -968.9 +/- 4.1 kJ mol(-1) at 0 and 298 K, respectively, and Delta H-f(298K)[Cr(CO)(6), c] = -1040.6 +/- 4.2 kJ mol(-1) for the crystalline state, based on the known enthalpy of sublimation. The measured Cr-CO bond dissociation energies in [(CO)(n)Cr-CO](+) (n= 0-5), and the enthalpies of formation of the chromium carbonyl ion series are also reported. (C) 2018 Published by Elsevier B.V.