一个由意大利佩鲁贾大学Nadia Balucani带领的合作研究团队宣布他们发现了O(³P)和吡啶反应的入口通道处的系间跨越。这一研究成果发表在2022年9月29日出版的国际学术期刊《自然-化学》上。

在该研究中，研究人员发现，在反应前络合物和反应势垒之间的系间跨越可以控制弱耦合势能面的双分子反应速率，即使在缺乏重原子的情况下。对于O(³P)+吡啶——一个与燃烧、天体化学和生物化学有关的反应——交叉束实验表明，主要产物是吡咯和CO，这是通过自旋禁止环收缩机制获得的。

通过高阶量子化学计算和统计非绝热的分支分数计算，实验结果被解释为在O原子加到N原子孤对电子的高入口势垒之前，发生了有效的系间跨越。在低温到中等温度下，计算出的反应速率被证明是由系间跨越所支配的。

据了解，两种量子效应可以使反应在（将反应物与生成物隔开的）势垒以下的能量下发生，即隧穿效应和耦合势能面之间的系间跨越。

附：英文原文

Title: Intersystem crossing in the entrance channel of the reaction of O(3P) with pyridine

Author: Recio, Pedro, Alessandrini, Silvia, Vanuzzo, Gianmarco, Pannacci, Giacomo, Baggioli, Alberto, Marchione, Demian, Caracciolo, Adriana, Murray, Vanessa J., Casavecchia, Piergiorgio, Balucani, Nadia, Cavallotti, Carlo, Puzzarini, Cristina, Barone, Vincenzo

Issue&Volume: 2022-09-29

Abstract: Two quantum effects can enable reactions to take place at energies below the barrier separating reactants from products: tunnelling and intersystem crossing between coupled potential energy surfaces. Here we show that intersystem crossing in the region between the pre-reactive complex and the reaction barrier can control the rate of bimolecular reactions for weakly coupled potential energy surfaces, even in the absence of heavy atoms. For O(3P) plus pyridine, a reaction relevant to combustion, astrochemistry and biochemistry, crossed-beam experiments indicate that the dominant products are pyrrole and CO, obtained through a spin-forbidden ring-contraction mechanism. The experimental findings are interpreted—by high-level quantum-chemical calculations and statistical non-adiabatic computations of branching fractions—in terms of an efficient intersystem crossing occurring before the high entrance barrier for O-atom addition to the N-atom lone pair. At low to moderate temperatures, the computed reaction rates prove to be dominated by intersystem crossing.

DOI: 10.1038/s41557-022-01047-3

Source: ^{https://www.nature.com/articles/s41557-022-01047-3}