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首页> 外文期刊>RSC Advances >Photochemistry of methyl hypobromite (CH3OBr): excited states and photoabsorption spectrum
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Photochemistry of methyl hypobromite (CH3OBr): excited states and photoabsorption spectrum

机译：甲基次溴酸盐（CH3OBr）的光化学：激发态和光吸收光谱

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The singlet and triplet excited states of CH3OBr with excitation energies up to similar to 9.5 eV are studied using the multi-reference configuration interaction with singles and doubles method (MRCI-SD) and several single-reference methods, including time-dependent density functional theory (TD-DFT), coupled-cluster (linear-response CC2 and equation-of-motion CCSD and CCSD(T)), and algebraic diagrammatic construction (ADC(2)). Among the single-reference methods, coupled-cluster gives vertical excitation energies and oscillator strengths comparable to the MRCI-SD values for the majority of excited states. The absorption cross section in the gas phase in the region between 2 and 8.5 eV was simulated with CCSD using the nuclear ensemble approach. The computed spectrum predicts two intense absorption bands. The first band, peaked at similar to 7.0 eV, is induced by Rydberg excitation. The second band has a strong overlap between a broad sigma sigma* transition and three Rydberg transitions, resulting in two peaks at 7.7 and 7.9 eV. The spectrum also features a low-intensity band peaking at similar to 4.6 eV due to n sigma* excitation. The intensity of this band is influenced by spin-orbit coupling effects. We analyzed the dissociation pathways along the O-Br and C-O coordinates by computing rigid potential energy curves of the ground and the lowest-lying singlet and triplet excited states, and discussed the possible dissociation products. Due to the specific electronic structure of the excited states, characterized by multireference, double excitations, and Rydberg states occurring in the low-energy region, their correct description along dissociation coordinates is feasible only with MRCI-SD.
机译：利用单参考和双精度方法（MRCI-SD）的多参考构型相互作用以及包括时变密度泛函理论在内的几种单参考方法，研究了CH3OBr激发能高达9.5 eV的单重态和三重态激发态。 （TD-DFT），耦合集群（线性响应CC2和运动方程CCSD和CCSD（T））以及代数图解结构（ADC（2））。在单参考方法中，耦合簇给出的垂直激发能量和振荡器强度与大多数激发态的MRCI-SD值相当。使用核集成方法用CCSD模拟了2至8.5 eV之间区域中气相的吸收截面。计算出的光谱预测出两个强烈的吸收带。第一频带的峰值约为7.0 eV，由里德堡激发。第二个波段在宽的sigma sigma *跃迁与三个Rydberg跃迁之间有很强的重叠，从而在7.7 eV和7.9 eV处出现两个峰值。由于n sigma *激发，该光谱还具有一个低强度峰，峰值接近4.6 eV。该频带的强度受自旋轨道耦合效应的影响。我们通过计算地面的刚性势能曲线和最低的单重态和三重态激发态，分析了沿O-Br和C-O坐标的解离途径，并讨论了可能的解离产物。由于激发态的特定电子结构具有在低能量区域中发生的多参考，双激发和Rydberg态的特征，因此沿解离坐标的正确描述仅适用于MRCI-SD。

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