Rotational and nuclear-spin level dependent photodissociation dynamics of H2S

The detailed features of molecular photochemistry are key to understanding chemical processes enabled by non-adiabatic transitions between potential energy surfaces. But even in a small molecule like hydrogen sulphide (H2S), the influence of non-adiabatic transitions is not yet well understood. Here we report high resolution translational spectroscopy measurements of the H and S(1D) photoproducts formed following excitation of H2S to selected quantum levels of a Rydberg state with 1B1 electronic symmetry at wavelengths λ ~ 139.1 nm, revealing rich photofragmentation dynamics. Analysis reveals formation of SH(X), SH(A), S(3P) and H2 co-fragments, and in the diatomic products, inverted internal state population distributions. These nuclear dynamics are rationalised in terms of vibronic and rotational dependent predissociations, with relative probabilities depending on the parent quantum level. The study suggests likely formation routes for the S atoms attributed to solar photolysis of H2S in the coma of comets like C/1995 O1 and C/2014 Q2.

Comparison of the Performances of Different Computational Methods to Calculate the Electrochemical Stability of Selected Ionic Liquids

The electrochemical stability windows (ESW) of selected ionic liquids have been calculated by comparing different computational approaches previously suggested in the literature. The molecular systems under study are based on di-alkyl imidazolium and tetra-alkyl ammonium cations coupled with two different imide anions (namely, bis-fluorosulfonyl imide and bis-trifluoromethyl sulfonyl imide), for which an experimental investigation of the ESW is available. Thermodynamic oxidation and reduction potentials have here been estimated by different models based on calculations either on single ions or on ionic couples. Various Density Functional Theory (DFT) functionals (MP2, B3LYP, B3LYP including a polarizable medium and empirical dispersion forces) were exploited. Both vertical and adiabatic transitions between the starting states and the oxidized or reduced states were considered. The approach based on calculations on ionic couples is not able to reproduce the experimental data, whatever the used DFT functional. The best quantitative agreement is obtained by calculations on single ions when the MP2 functional in vacuum is considered and the transitions between differently charged states are vertical (purely electronic without the relaxation of the structure). The B3LYP functional underestimates the ESW. The inclusion of a polar medium excessively widens the ESW, while a large shrinkage of the ESW is obtained by adopting an adiabatic transition scheme instead of a vertical transition one.

Molecular Polaritons Generated from Strong Coupling between CdSe Nanoplatelets and a Dielectric Optical Cavity

We demonstrate the formation of CdSe nanoplatelet (NPL) exciton-polaritons in a distributed bragg reflector (DBR) cavity. The molecule-cavity hybrid system is in the strong coupling regime with an 83 meV Rabi splitting, characterized from angle-resolved reflectance and photoluminescence measurements. Mixed quantum-classical dynamics simulations are used to investigate the polariton photo-physics of the hybrid system by treating the electronic and photonic degree of freedom (DOF) quantum mechanically, and the nuclear phononic DOF classically. Our numerical simulations of the angle-resolved photoluminescence (PL) agree excellently with the experimental data, providing a fundamental explanation of the asymmetric intensity distribution of the upper and lower polariton branches. Our results also provide mechanistic insights into the importance of phonon-assisted non-adiabatic transitions among polariton states which are reflected in the various features of the PL spectra. Our work proves the feasibility of coupling nanoplatelets into a dielectric cavity to form a hybrid system and provides a new platform for investigating cavity-mediated physical and chemical processes.

Molecular Polaritons Generated from Strong Coupling between CdSe Nanoplatelets and a Dielectric Optical Cavity

We demonstrate the formation of CdSe nanoplatelet (NPL) exciton-polaritons in a distributed bragg reflector (DBR) cavity. The molecule-cavity hybrid system is in the strong coupling regime with an 83 meV Rabi splitting, characterized from angle-resolved reflectance and photoluminescence measurements. Mixed quantum-classical dynamics simulations are used to investigate the polariton photo-physics of the hybrid system by treating the electronic and photonic degree of freedom (DOF) quantum mechanically, and the nuclear phononic DOF classically. Our numerical simulations of the angle-resolved photoluminescence (PL) agree excellently with the experimental data, providing a fundamental explanation of the asymmetric intensity distribution of the upper and lower polariton branches. Our results also provide mechanistic insights into the importance of phonon-assisted non-adiabatic transitions among polariton states which are reflected in the various features of the PL spectra. Our work proves the feasibility of coupling nanoplatelets into a dielectric cavity to form a hybrid system and provides a new platform for investigating cavity-mediated physical and chemical processes.

К теории инициирующего действия непрерывного нагрева на структурные перестройки и температуру фазового перехода в кристаллах

A model and kinetic theory of structural changes in crystals upon continuous heating are proposed. Nonadiabatic transitions of atoms between different states of a system of nuclei and electrons are taken into account. Non-adiabatic transitions initiate structural rearrangements determined by a change in the short-range order upon the redistribution of electron density. It was shown that continuous heating stimulates structural changes in the crystal and lowers the temperature of a known phase transition.