Researchers from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) have developed a novel method for precisely imaging molecular structures using highly charged ions, as detailed in their study published in Physical Review Letters. This new approach utilizes a Coulomb explosion triggered by highly charged ions, demonstrating its effectiveness as a unique tool for detailed visualization of complex molecules, particularly overcoming the limitations faced in earlier techniques.
Coulomb explosion imaging (CEI) is a powerful technique for capturing molecular structures with atomic-scale resolution. Historically, CEI has relied on the use of intense laser pulses or X-ray pulses, which, despite their effectiveness, have been restricted to analyzing simple molecules with five or fewer atoms. These traditional methods have faced significant challenges in measuring bond lengths with high precision, particularly when hydrogen atoms are involved due to their light mass and the difficulty in tracking their positions accurately.
The breakthrough achieved by the IMP research team involved using highly charged ions rather than traditional laser or X-ray methods. In their experiment, the team utilized the C5+ ion beam at an energy of 112.5 eV/u at the Heavy Ion Research Facility in Lanzhou (HIRFL) to induce a Coulomb explosion in C4H4N2 (pyrazine) molecules. By exposing these complex molecules to a highly intense and ultra-short pulse of an electronic field, more than ten electrons were stripped away from the molecules in less than one femtosecond. According to Prof. Xu Shenyue, one of the corresponding authors of the study, this rapid electron removal is crucial for achieving high-precision imaging, especially of light atoms like hydrogen.
To capture the resulting explosion and extract structural information, the researchers employed reaction microscopy, which allowed them to record the trajectories of ionic fragments such as H+, C2+, C+, and N+. By reconstructing the momentum vectors of these fragments, they were able to generate highly accurate images of the molecule’s atomic structure. This method enabled the precise identification of both hydrogen and heavier atoms within the molecule, offering a significant advancement over previous techniques that struggled with the accurate positioning of hydrogen atoms.
One of the key findings from this study was the ability of the accelerator-based CEI approach to image molecules containing up to ten atoms with high precision. Additionally, the researchers found that analyzing the angular correlation between the fragments produced during the explosion could serve as a “fingerprint” for identifying different isomeric forms of a molecule. This capability opens up new possibilities for distinguishing between molecules that have the same chemical formula but different structural arrangements.
Prof. Ma Xinwen, another corresponding author, emphasized that using highly charged ions for CEI represents a unique and powerful approach to studying complex molecules. The success of this method in resolving molecular structures with atomic-level accuracy suggests a promising future for the application of accelerators in the field of molecular imaging. This study not only enhances our ability to study molecular structures but also has the potential to advance research in areas such as chemical reaction dynamics, materials science, and biological systems, where understanding molecular structures with precision is critical.
Source: Chinese Academy of Sciences