Photochemical reactions of the low-lying excited states of formaldehyde: T1/S0 intersystem crossings, characteristics of the S1 and T1 potential energy surfaces, and a global T1 potential energy surface.
Photochemical reactions of the low-lying excited states of formaldehyde: T1/S0 intersystem crossings, characteristics of the S1 and T1 potential energy surfaces, and a global T1 potential energy surface.
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DOI：
10.1063/1.3085952
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发表时间：
2009-03
期刊：
影响因子：
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通讯作者：
Peng Zhang;S. Maeda;K. Morokuma;B. Braams
中科院分区：
文献类型：
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作者：
Peng Zhang;S. Maeda;K. Morokuma;B. Braams
利用多参考构型相互作用方法进行了精确的从头计算，以表征甲醛（H(2)CO）和羟甲基（HCOH）的低激发态(S（1)和T(1)）的势能面（PESs），重点研究了它们的异构化、解离以及T(1)态在H(2)CO的非绝热光解离中的可能作用。发现T(1) PES上的两个区域有助于向基态（S(0)）的非绝热转变。交叉缝（MSXs）上的3个极小值（80 ~ 85 kcal/mol，高于S(0)全球极小值）位于HCOH区；然而，它们被大约107千卡/摩尔的高能异构化过渡态所阻挡。在H(2)CO区发现的另一个MSX，能量</=91 kcal/mol，自旋轨道相互作用强；这可能是T(1)到S(0)转变的一个更重要的途径。对T(1)态生成一个全维PES，通过采用多体展开的加权最小二乘法拟合，其中每一项都是核间距离的函数，并且在类似原子的排列下是不变的。单一的全局功能涵盖甲醛和HCOH区域以及解离途径。拟合的PES质量很高，其均方根拟合误差很小，为119 cm(-1)，从头计算的临界点与拟合的PES非常接近。
Accurate ab initio calculations using the multireference configuration interaction method have been performed to characterize the potential energy surfaces (PESs) of low-lying excited states (S(1) and T(1)) of formaldehyde (H(2)CO) and hydroxymethylene (HCOH) with emphasis on their isomerization, dissociation, and the possible role of the T(1) state in the nonadiabatic photodissociation of H(2)CO. Two regions on the T(1) PES are found to contribute to the nonadiabatic transition to the ground (S(0)) state. Three minima on the seam of crossing (MSXs), 80-85 kcal/mol (above the S(0) global minimum), are located in the HCOH region; they, however, are blocked by a high-energy isomerization transition state at approximately 107 kcal/mol. The other MSX discovered in the H(2)CO region is reachable with energy </=91 kcal/mol and strong spin-orbit interaction; this may be a more important pathway for the T(1) to S(0) transition. A full-dimensional PES is generated for the T(1) state, fitted by a weighted least-squares method employing a many-body expansion in which each term is a function of the internuclear distances and is invariant under permutations of like atoms. The single global function covers the formaldehyde and the HCOH regions as well as dissociation pathways. The high quality of the fitted PES is demonstrated by the small root-mean-square fitting error of 119 cm(-1) and the close agreement between the critical points from ab initio calculations and from the fitted PES.