spatial confinement
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2022 ◽  
Vol 9 ◽  
Author(s):  
Marta Chołuj ◽  
Josep M. Luis ◽  
Wojciech Bartkowiak ◽  
Robert Zaleśny

Infrared (IR) spectroscopy is commonly used in chemical laboratories to study the geometrical structure of molecules and molecular complexes. The analysis of experimental IR spectra can nowadays be reliably supported by the results of quantum-chemical computations as vibrational frequencies and corresponding vibrational transition intensities are routinely calculated using harmonic approximation by virtually all quantum chemistry packages. In the present study we combine the methodology of computing vibrational spectra using high-level electron correlation treatments with an analytical potential-based approach to take into account spatial confinement effects. Using this approach, we perform a pioneering analysis of the impact of the spatial confinement caused by a cylindrical harmonic oscillator potential on the harmonic vibrational transition intensities and frequencies of two hydrogen-bonded complexes: HCN…HCN and HCN…HNC. The emphasis is put on the largest-intensity bands, which correspond to the stretching vibrations. The obtained results demonstrate that embedding the molecular complexes in an external confining potential causes significant changes of transition intensities and vibrational frequencies.


2021 ◽  
Vol 933 ◽  
Author(s):  
Francesco Picella ◽  
Sébastien Michelin

To spontaneously break their intrinsic symmetry and self-propel at the micron scale, isotropic active colloidal particles and droplets exploit the nonlinear convective transport of chemical solutes emitted/consumed at their surface by the surface-driven fluid flows generated by these solutes. Significant progress was recently made to understand the onset of self-propulsion and nonlinear dynamics. Yet, most models ignore a fundamental experimental feature, namely the spatial confinement of the colloid, and its effect on propulsion. In this work the self-propulsion of an isotropic colloid inside a capillary tube is investigated numerically. A flexible computational framework is proposed based on a finite-volume approach on adaptative octree grids and embedded boundary methods. This method is able to account for complex geometric confinement, the nonlinear coupling of chemical transport and flow fields, and the precise resolution of the surface boundary conditions, that drive the system's dynamics. Somewhat counterintuitively, spatial confinement promotes the colloid's spontaneous motion by reducing the minimum advection-to-diffusion ratio or Péclet number, ${Pe}$ , required to self-propel; furthermore, self-propulsion velocities are significantly modified as the colloid-to-capillary size ratio $\kappa$ is increased, reaching a maximum at fixed ${Pe}$ for an optimal confinement $0<\kappa <1$ . These properties stem from a fundamental change in the dominant chemical transport mechanism with respect to the unbounded problem: with diffusion now restricted in most directions by the confining walls, the excess solute is predominantly convected away downstream from the colloid, enhancing front-back concentration contrasts. These results are confirmed quantitatively using conservation arguments and lubrication analysis of the tightly confined limit, $\kappa \rightarrow 1$ .


ACS Nano ◽  
2021 ◽  
Author(s):  
Dongjun Li ◽  
Bingbing Gong ◽  
Xiaolong Cheng ◽  
Fangxin Ling ◽  
Ligong Zhao ◽  
...  

Fuel ◽  
2021 ◽  
Vol 306 ◽  
pp. 121722
Author(s):  
An Guo ◽  
Yumei Peng ◽  
Mingyue Mao ◽  
Yi Wang ◽  
Yan Long ◽  
...  

2021 ◽  
Vol 119 (20) ◽  
pp. 203501
Author(s):  
Etienne Coffy ◽  
Sébastien Euphrasie ◽  
Pascal Vairac ◽  
Abdelkrim Khelif

2021 ◽  
Vol 294 ◽  
pp. 120254
Author(s):  
Lili Huo ◽  
Xi Han ◽  
Luyao Zhang ◽  
Baocang Liu ◽  
Rui Gao ◽  
...  

Molecules ◽  
2021 ◽  
Vol 26 (19) ◽  
pp. 5924
Author(s):  
Paweł Lipkowski ◽  
Justyna Kozłowska ◽  
Wojciech Bartkowiak

In this theoretical study, we report on the molecular electrostatic potential (MEP) of titled molecules confined by repulsive potentials of cylindrical symmetry mimicking a topology. Our calculations show that the spatial restriction significantly changes the picture of the MEP of molecules in a quantitative and qualitative sense. In particular, the drastic changes in the MEP as a function of the strength of spatial confinement are observed for the BrCN molecule. This preliminary study is the first step in the investigation of the behavior of the MEP of molecular systems under orbital compression.


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