Postponed

THIS SEMINAR HAS BEEN POSPONED IN SOLIDARITY WITH STAFF STRIKING. 

All the chemical and physical processes in our universe are ruled by thermodynamic variables such as pressure, temperature, and chemical potential [1]: acting on one of these variables allows to modify the equilibrium composition of molecular systems and the kinetics of their transformations. Among these thermodynamic variables, pressure has demonstrated to be a very powerful tool to affect the behaviour of molecular systems, generally regarded as highly compressible [1,2]: the application of pressures in the range of 1-10 GPa significantly reduces the intermolecular distances in such systems, leading to enhanced interactions. It becomes possible to explore this way different regions of molecular systems potential energy surfaces, reaching otherwise inaccessible new local or global energy minima and observing a huge variety of phenomena ranging from phase transitions to amorphisations, and, in more drastic conditions, to a complete reorganisation of the chemical bonding connection scheme, leading to unexpected chemical reactivity with the formation of new products. Nowadays, well-established high-pressure techniques allow to perform experiments in a wide range of pressures (up to the megabar) and temperatures (from 10 to thousands of Kelvin), thus accessing a huge variety of phenomena that are of paramount interest for fundamental and technological issues in diverse fields such as geophysics, astrochemistry, fundamental physics and chemistry and materials science, with regard to the synthesis of novel and intriguing materials that can be recovered at ambient conditions.

In the general framework of high-pressure chemical reactivity, photo-induced processes are particularly interesting for opening new paths to the synthesis of complex molecules starting from very simple reagents and using only physical tools (p, T, hν): among several examples, this is the case for red phosphorus/ammonia mixtures [6], or for laser-heated DAC experiments in black phosphorus/hydrogen mixtures [7]. On the other hand, pressure-driven chemical reactions occurring under extreme spatial confinement set favourable conditions for the synthesis of nanocomposite materials with intriguing properties: a good insight on this topic is offered by the polymerization of simple molecules (acetylene, CO) within the inorganic scaffold provided by synthetic, non-catalytic zeolites [3,4,5]. At last, in the context of geophysics and fundamental chemistry, the speciation of carbon dioxide in pressure and temperature conditions relevant to those of the Earth’s lower mantle is of paramount interest for a deeper comprehension of its complex chemistry: recent results have shown the substantial stability of CO2 in its polymeric phase CO2-V within this range [8,9].

References

[1] R. Bini and V. Schettino, Materials Under Extreme Conditions – Molecular Crystals at High Pressure. Imperial College Press, 2013.

[2] V. Schettino et al., “Chemical reactions at very high pressure,” in Advances in Chemical Physics (S. A. Rice, ed.), vol. 131, pp. 105– 242, John Wiley & Sons,Inc., 2005.

[3] D. Scelta et al., Chem. Mater., 26, 7, 2249–2255, 2014.

[4] M. Santoro, K. F. Dziubek, D. Scelta et al., Chem. Mater., 27, 19, 6486–6489, 2015. [5] M. Santoro, D. Scelta et al., Chem. Mater., 28, 11, 4065–4071, 2016.

[6] D. Scelta et al., J. Phys. Chem. C, 124, 7, 4308–4319, 2020.

[7] M. Ceppatelli, D. Scelta et al., Nature Communications,11, 6125, 2020.

[8] K. F. Dziubek, M. Ende, D. Scelta et al., Nature Communications, 9, 3148, 2018.

[9] D. Scelta et al., Phys. Rev. Lett., 126, 065701, 2021.

 

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