Ultra-low-temperature reactions of C and Si atoms inside superfluid helium nanodroplets

点击翻译按钮获取中文摘要

Carbon and silicon are the main components of refractory dust grains in astrophysical environments. There are strong arguments in favor of the fact that the dust formation occurs directly in the cold regions of the interstellar medium (ISM). This project is devoted to the study of chemical reactions involving C and Si atoms, which could be relevant to the formation of refractory dust in the ISM. The reactions will be studied at ultra-low-temperature (T = 0.37 K) in superfluid helium nanodroplets. The reactions proceeding at this temperature have no energy barrier and, therefore, they are expected to be fast in the entire low-temperature range encountered in the ISM. At the beginning of the project, we will improve the accuracy of the calorimetric technique to measure more precisely the reaction energies. During the later stages of the project, the developed technique, in combination with quantum chemical calculations, will be used for the determination of the active reaction channels. The reactions of C and Si atoms with molecules modeling the surface of astrophysical dust grains will be studied. Diamondoid molecules will simulate the hydrogenated diamond surface while large polycyclic aromatic hydrocarbon (PAH) molecules are close analogues of the graphite surface and small silicate clusters mimic the surface of silicate grains. The observation of strong chemical bonds in our experiments will demonstrate high binding energies between the corresponding atoms and surfaces. Apart from studying the reactivity of individual species, we will also focus on the condensation of carbon atoms inside helium droplets. Large helium droplets containing millions or even billions of He atoms will be used to pick up gas-phase carbon atoms and condense them. The formed carbon nanoparticles and possibly nanowires will be deposited on appropriate substrates and analyzed by high-resolution transmission electron microscopy (HRTEM), UV/VIS and IR absorption spectroscopy, Raman spectroscopy, and atomic force microscopy (AFM). These studies will reveal the preferred allotropic form of the carbonaceous material produced by low-temperature condensation of carbon atoms. The spectral properties of the produced carbon nanoparticles will be studied and compared with the astrophysical observations. Moreover, the properties of carbon nanowires, which are expected to be formed in the largest helium droplets, should be particularly interesting for applications in nanoelectronics.