近日，美国布朗大学Lai-Sheng Wang团队报道了CBi^-中经典三键的相对论坍缩分子离子。这一研究成果于2026年7月9日发表在《科学》杂志上。

在传统的主族元素化学键框架中，多重键通过分开的σ轨道和π轨道来描述。然而，对于含重元素的分子，相对论效应通过自旋-轨道耦合将这些轨道混合，使得总角动量投影（ω）成为唯一的好量子数。关于相对论效应会改变σ-π成键框架的直接实验证据至今仍难以获得。

研究组利用高分辨率低温光电子能谱，并结合相对论四分量Dirac-Coulomb耦合簇计算，探测了CBi^-阴离子中的碳-铋三键。尽管CBi^-阴离子与众所周知的CN^-物种是等电子体，但研究组证明，传统的σ + 2π三键图像会坍缩为一个纯π特征的|ω| = 3/2态和两个包含显著σ/π混合的|ω| = 1/2 Kramers对。

附：英文原文

Title: Relativistic collapse of the classical triple bond in the CBi molecular ion

Author: Deniz Kahraman, Jie Hui, Xin-Yu Zhang, Neil A. Ellis, Hyun Wook Choi, Kirk A. Peterson, Lai-Sheng Wang

Issue&Volume: 2026-07-09

Abstract: The conventional framework for chemical bonding between main-group elements involves separate σ and π orbitals to describe multiple bonds. However, relativistic effects mix these orbitals in molecules containing heavy elements through spin–orbit coupling, leaving the total angular-momentum projection (ω) as the only good quantum number. Direct experimental evidence that relativistic effects change the σ-π bonding framework has remained elusive. Here, we probe the carbon-bismuth triple bond in the CBi anion using high-resolution cryogenic photoelectron spectroscopy, coupled with relativistic four-component Dirac-Coulomb coupled-cluster calculations. Even though the CBi anion is isovalent to the well-known CN species, we demonstrate that the traditional σ + 2π triple-bond picture collapses into a pure π-like |ω| = 3/2 and two |ω| = 1/2 Kramers pairs containing substantial σ/π mixing.

DOI: aei1285

Source: https://www.science.org/doi/10.1126/science.aei1285