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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Formic Acid Dimerization: Evidence for Species Diversity from First Principles Simulations
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Formic Acid Dimerization: Evidence for Species Diversity from First Principles Simulations

机译：甲酸二聚化：基于第一性原理模拟的物种多样性证据

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摘要

Dimerization of formic acid has been simulated using ab initio molecular dynamics at conditions mimicking rare gas matrix isolation experiments. Aggregation product distributions and the corresponding reaction pathways have been studied as a function of temperature. At higher temperatures, the cyclic, C_(2h) symmetric, global minimum structure A with two 0_H_ _ _ 0=C hydrogen bonds predominates over the second most stable, acyclic, local minimum isomer B with one 0_H_ _ _ 0=C and one C_H_ _ _ 0=C hydrogen bond, whereas the latter is the main species at low temperature. Significant concentrations of two additional, less stable, local minimum species, C exhibiting an 0_H _ _ _ 0=C and an 0_H _ _ _ O(H)_C hydrogen bond, and D with an 0_H _ _ _ O(H)_C and a C_H _ _ _ 0=C hydrogen bond, which should be detectable in experiment, are predicted at low temperature. Theoretical vibrational spectra are provided to guide the experimental search for these species. Furthermore, free-energy barriers for thermal interconversion of different dimer species have been calculated using targeted molecular dynamics in conjunction with thermodynamic integration. The small barrier for the C → A reaction of 7.0 kJ/mol indicates that the C species can only be stabilized at ultracold conditions. The data presented here thus hold important clues for the execution and interpretation of low-temperature vibrational spectroscopy at matrix isolation or ultracold helium droplet conditions.
机译：在模拟稀有气体基质分离实验的条件下，使用从头算分子动力学模拟了甲酸的二聚化。已经研究了聚集产物分布和相应的反应路径随温度的变化。在较高的温度下，具有两个0_H_ _ _ 0 = C氢键的环状C_（2h）对称全局最小结构A优先于第二个最稳定，无环的局部最小异构体B，其中一个0_H_ _ _0 == C和一个C_H ___ 0 = C氢键，而后者是低温下的主要种类。浓度较高的另外两个不稳定的局部最小值物种，C表现为0_H _ _ _ = O = H和0_H _ _ O（H）_C氢键，D的表现为0_H _ _ O_（H）_C预测在低温下应能在实验中检测到的C_H _ _ _0 = C氢键。提供理论振动光谱以指导对这些物种的实验搜索。此外，使用目标分子动力学结合热力学积分，已经计算出了不同二聚体物种进行热转化的自由能势垒。 C→A反应7.0 kJ / mol的小势垒表明C物种只能在超冷条件下稳定。因此，此处提供的数据为在基质隔离或超冷氦滴条件下执行和解释低温振动光谱学提供了重要线索。

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