密度函数理论和初始分子动力学揭示了碳酸盐聚类同位素重排序的原子机制
Saul Perez-Beltran1,2, Wasif Zaheer1,2, Zeyang Sun3
1Department of Chemistry, Texas A&M University, College Station, TX 77843, USA.
Science advances
|June 28, 2023
概括
碳酸盐中的聚合同位素温度计受温度诱导的重新排序的影响. 这项研究揭示了原子化机制,显示了杂质和水如何加速石灰岩古热度计中的同位素交换.
科学领域:
- 地质化学 地质化学
- 同位素地球化学 同位素地球化学
- 计算矿物学是指计算机矿物学.
背景情况:
- 碳酸盐中聚集的同位素 (C-O) 作为古热度计,但它们的信号因沉积后的温度变化 (重新排序) 而改变.
- 以前的研究发现了影响重排速率的因素,如杂质和水,但缺乏对机制的详细原子学理解.
研究的目的:
- 通过第一原则模拟,研究石中凝聚的同位素重排的原子化机制.
- 阐明杂质 (Mg2+替代,Ca2+空缺) 和水在促进同位素交换中的作用.
主要方法:
- 使用第一原理模拟来建模碳酸盐对在石中的同位素交换反应.
- 计算的重点是确定重新排序路径的自由激活能量 (ΔA‡).
主要成果:
- 确定了用于同位素交换的首选原子结构.
- 发现Mg2+替代和Ca2+空缺可以显著降低重新排序的激活能量障碍.
- 一个由水介导的交换机制,涉及化四协调碳中间体,证明了最低的激活能量,证实了水的催化作用.
结论:
- 这项研究提供了一个详细的原子模型,用于碳酸结合的同位素重新排序.
- 污染物和水的存在被证实是加速重新排序过程的关键因素,影响古气温重建.
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