The team of Zhen Junfeng and Qin Liping from the School of Earth and Space Sciences of our University has made new progress in the formation and evolution of complex organic cluster molecules. The results provide a gas-phase growth path for the formation of complex organic compounds during the bottom-up growth of interstellar macromolecules, and provide theoretical and experimental data support for further understanding of their chemical evolution behavior in the interstellar medium. The research results were published on July 16 in the international academic journal Astronomy & Astrophysics.

Interstellar complex organic molecules are thought to be part of more complex organic compounds and even an important component of living matter (see Figure 1). Organic molecules are known to exist in star forming regions and in protoplanetary disks where planets form. However, free organic molecules in the gas phase are easily destroyed by ultraviolet light, and the energy of a single ultraviolet photon can dissociate these molecules. Polycyclic aromatic compounds and their derivatives may play an important role in the evolution of complex organic compounds. Large polycyclic aromatic compounds or clusters and very small dust particles can effectively protect these vaporous organic molecules from being destroyed by ultraviolet dissociation.

Figure I. Evolutionary paths of complex organic molecules in interstellar space

In this work, the research team used the self-built experimental instrument platform to study the stability of organic molecular-polycyclic aromatic hydrocarbon clusters in the process of ion-molecule collision reaction and the path of accumulation formation: Massive polycyclic aromatic cations (dihalonene C48H20+) and organic molecules (pyroglutamine, C5H9NO2) as reactants are formed and evolved (see Figure II, The experimental results have been published in Hu et al.Astronomy & Astrophysics, 2021, 656, A80). A series of theoretical calculations were made for the formation of polycyclic aromatic organic molecular clusters ((C5H9NO2)1-6C48+, n=[1,6]) (see Figure 3).

Figure 2. Mass spectra obtained from the reaction of DC+ with pyroglutamine

Figure 3. Tree growth diagram shows the growth path of (C5H9NO2)1-6C48+ cluster molecules

Experimental and theoretical studies have shown that complex organic molecules or other related prelife molecules can be efficiently adsorbed on small dust particles in the interstellar medium. According to experimental and theoretical results, ion-molecular reactions occur between (C5H9NO2)1-6C48+, n=[0,5]) and C5H9NO2, and there are a large number of reaction pathways that can produce very complex and massive molecular clusters with three-dimensional structures. These molecular clusters (graphene-organic molecular clusters) provide possible pathways for the formation and chemical evolution of large complex pre-life molecules from the bottom up in the interstellar medium. The ion-molecule reaction synthesis route is crucial for the study of interstellar chemistry and shows that gas-phase interstellar matter can directly form large complex organic derivatives during bottom-up growth. The generation of these interesting pre-life molecular clusters provides a deeper understanding of how organic molecules evolve in interstellar space. The results also show that organic molecules can accumulate on small dust particles in the interstellar medium (for example, massive polycyclic aromatic hydrocarbons or graphene), while this accumulation process also supports the idea that pre-life molecules can be delivered to Earth via comets, meteorites or interstellar dust particles.

The first author of the paper is Zhen Junfeng from the University of Science and Technology of China and Yang Yuanyuan, a doctoral candidate in Qin Liping's research group. The research was supported by the Strategic Pilot Science and Technology Project of the Chinese Academy of Sciences (XDB 41000000) and the National Natural Science Foundation of China (12073027, 41625013, 21827804). The theoretical calculation work of the paper was completed at the Supercomputing Center of the University of Science and Technology of China.

Paper link：https://www.aanda.org/articles/aa/full_html/2022/07/aa43386-22/aa43386-22.html

(School of Earth and Space Sciences)
Source: HKUST News Network