ABSTRACT An alternative to the transition state (TS) pathway, the roaming route, which bypasses the minimum energy path but produces the same molecular products, was recently found in photodissociation dynamics. This account describes signatures of roaming in photodissociation of the carbonyl compounds, specifically methyl formate and aliphatic aldehydes. Methyl formate was promoted to the excited state, followed by internal conversion via a conical intersection. Then, the energetic precursor dissociated to fragments which proceeded along either TS or roaming path. In contrast to the lack of a roaming saddle point found in methyl formate, the structure of the roaming saddle point for each of a series of aliphatic aldehydes comprises two moieties that are weakly bound at a distance. As its size increases, the energy difference between the TS barrier and the roaming saddle point increases and the roaming pathway becomes increasingly dominant. Experimentally, the rotational-level dependence of the roaming route was measured with ion imaging, while the vibrational-state dependence was observed with time-resolved Fourier-transform infrared emission spectroscopy. The roaming signature was verified theoretically by quasi-classical trajectory (QCT) calculations. As an alternative to the QCT method, a multi-center impulsive model was developed to simulate the roaming scalar and vector properties.

中文翻译：

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羰基化合物光解中的漫游特征

摘要 最近在光解动力学中发现了一种替代过渡态 (TS) 途径的漫游途径，它绕过最小能量路径但产生相同的分子产物。该帐户描述了羰基化合物（特别是甲酸甲酯和脂肪族醛）在光解中漫游的特征。甲酸甲酯被提升到激发态，然后通过锥形交叉进行内部转化。然后，能量前驱体解离为沿着 TS 或漫游路径前进的碎片。与在甲酸甲酯中发现的缺乏漫游鞍点相反，一系列脂族醛中每一个的漫游鞍点结构包含两个在一定距离处弱结合的部分。随着其规模的增加，TS 屏障和漫游鞍点之间的能量差异增加，漫游路径变得越来越占主导地位。实验上，漫游路线的旋转水平依赖性用离子成像测量，而振动状态依赖性用时间分辨傅立叶变换红外发射光谱观察。通过准经典轨迹（QCT）计算从理论上验证了漫游签名。作为 QCT 方法的替代方法，开发了一种多中心脉冲模型来模拟漫游标量和矢量特性。而通过时间分辨傅立叶变换红外发射光谱观察到振动状态依赖性。通过准经典轨迹（QCT）计算从理论上验证了漫游签名。作为 QCT 方法的替代方法，开发了一种多中心脉冲模型来模拟漫游标量和矢量特性。而通过时间分辨傅立叶变换红外发射光谱观察到振动状态依赖性。通过准经典轨迹（QCT）计算从理论上验证了漫游签名。作为 QCT 方法的替代方法，开发了一种多中心脉冲模型来模拟漫游标量和矢量特性。