Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-980Curitiba, Paraná, Brazil.
ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000Aarhus C, Denmark.
J Phys Chem A. 2023 Feb 16;127(6):1445-1457. doi: 10.1021/acs.jpca.2c08023. Epub 2023 Feb 2.
High-resolution photoabsorption cross-sections in the 3.7-10.8 eV energy range are reinvestigated for nitromethane (CHNO), while for nitroethane (CHNO), they are reported for the first time. New absorption features are observed for both molecules which have been assigned to vibronic excitations of valence, Rydberg, and mixed valence-Rydberg characters. In comparison with nitromethane, nitroethane shows mainly broad absorption bands with diffuse structures, which can be interpreted as a result of the side-chain effect contributing to an increased number of internal degrees of freedom. New theoretical quantum chemical calculations performed at the time-dependent density functional theory (TD-DFT) level were used to qualitatively help interpret the recorded photoabsorption spectra. From the photoabsorption cross-sections, photolysis lifetimes in the terrestrial atmosphere have been obtained for both compounds. Relevant internal conversion from Rydberg to valence character is noted for both molecules, while the nuclear dynamics of CHNO and CHNO along the C-N reaction coordinate have been evaluated through potential energy curves at the TD-DFT level of theory, showing that the pre-dissociative character is more prevalent in nitromethane than in nitroethane.
在 3.7-10.8 eV 能量范围内，重新研究了硝基甲烷（CHNO）的高分辨率光吸收截面，而对于硝基乙烷（CHNO），则首次报道了其光吸收截面。这两种分子都观察到了新的吸收特征，这些特征被归因于价电子、里德堡和混合价-里德堡激发的振子激发。与硝基甲烷相比，硝基乙烷主要显示出具有漫射结构的宽吸收带，这可以解释为侧链效应导致内部自由度增加的结果。新的理论量子化学计算是在含时密度泛函理论（TD-DFT）水平上进行的，用于定性地帮助解释记录的光吸收光谱。从光吸收截面中，获得了这两种化合物在地球大气中的光解寿命。对于这两种分子，都注意到了从里德堡到价电子的相关内部转换，而通过在 TD-DFT 理论水平上的势能曲线，评估了 CHNO 和 CHNO 沿 C-N 反应坐标的核动力学，表明预解离特征在硝基甲烷中比在硝基乙烷中更为普遍。
