Carbon nanotubes immersed in superfluid helium: the Impact of quantum confinement on wetting and capillary action

7 págs.; 5 figs.; 1 tab. ; Associated content mp4 video: http://pubs.acs.org/doi/suppl/10.1021/acs.jpclett.6b02414A recent experimental study [Ohba, Sci. Rep. 2016, 6, 28992] of gas adsorption on single-walled carbon nanotubes at temperatures between 2 and 5 K reported a quenched propagation of helium through carbon nanotubes with diameters below 7 Å despite the small kinetic diameter of helium atoms. After assessing the performance of a potential model for the He−nanotube interaction via ab initio calculations with density functional theorybased symmetry adapted perturbation theory, we apply orbital-free helium density functional theory to show that the counterintuitive experimental result is a consequence of the exceptionally high zeropoint energy of helium and its tendency to form spatially separated layers of helium upon adsorption at the lowest temperatures. Helium filling factors are derived for a series of carbon nanotubes and compared to the available experimental data. © 2016 American Chemical SocietyThis work has been supported by the COST Action CM1405 “Molecules in Motion (MOLIM)”. M.P.d.L.-C. gratefully acknowledges support from MINECO (Spain) under Grant MAT2016-75354-P and thanks the CTI (CSIC) and CESGA supercomputer facilities (Spain) for the resources provided.Peer reviewe

Non-adiabatic Coupling In No@c60: Prediction Of A Renner-teller Like Effect For Spherically Encapsulated Diatomic Molecules

\begin{wrapfigure}{l}{0pt} \includegraphics[scale=0.15]{endo.eps} \end{wrapfigure} \noindent The Renner-Teller effect describes the coupling of a symmetry-reducing molecular vibration with a two-fold degenerate electronic state. Its discovery goes back to work of Herzberg and Teller, who realized in 1933 that the potential energy surface of a triatomic, linear molecule splits into two as soon as the molecule is bent. In this work, we show that a very similar, yet unknown type of non-adiabatic coupling can even occur for diatomic (!) molecules. \\ \smallskip \noindent This seems absurd at first sight, but becomes possible as soon as the diatomic molecule ist embedded in a spherically symmetric confinement. In this case, its translational degrees of freedom become quantized and can couple to electronically degenerate states in a very similar fashion as predicted by Renner-Teller effect theory. To our knowledge, it is the first time that this novel type of non-adiabatic coupling has been investigated either in theory or experiment.[1] \\ \smallskip \noindent We demonstrate this effect for the experimentally accessible case of NO embedding in a C$_{60}$. Endofullerenes, in particular those carrying a radical molecule, are highly topical objects of ongoing research in molecular spectroscopy, reaction chemistry and carbon-based nanomaterial design. Also, suitable confinements in molecular traps for quantum information and quantum computing will produce a similar effect of nonadiabatic coupling as predicted by our study. \\ \smallskip [1] A.W. Hauser and J.V. Pototschnig, J .Phys. Chem. A, 2022, DOI:10.1021/acs.jpca.1c1097

Communication: Dopant-induced solvation of alkalis in liquid helium nanodroplets

Alkali metal atoms and small alkali clusters are classic heliophobes and when in contact with liquid helium they reside in a dimple on the surface. Here we show that alkalis can be induced to submerge into liquid helium when a highly polarizable co-solute, C60, is added to a helium nanodroplet. Evidence is presented that shows that all sodium clusters, and probably single Na atoms, enter the helium droplet in the presence of C60. Even clusters of cesium, an extreme heliophobe, dissolve in liquid helium when C60 is added. The sole exception is atomic Cs, which remains at the surface

Vibronic transitions in the X-Sr series (X=Li, Na, K, Rb): on the accuracy of nuclear wavefunctions derived from quantum chemistry

Research on ultracold molecules has seen a growing interest recently in the context of high-resolution spectroscopy and quantum computation. The preparation of molecules in low vibrational levels of the ground state is experimentally challenging, and typically achieved by population transfer using excited electronic states. On the theoretical side, highly accurate potential energy surfaces are needed for a correct description of processes such as the coherent de-excitation from the highest and therefore weakly bound vibrational levels in the electronic ground state via couplings to electronically excited states. Particularly problematic is the correct description of potential features at large intermolecular distances. Franck-Condon overlap integrals for nuclear wavefunctions in barely bound vibrational states are extremely sensitive to inaccuracies of the potential at long range. In this study, we compare the predictions of common, wavefunction-based ab initio techniques for a known de-excitation mechanism in alkali-alkaline earth dimers. It is the aim to analyze the predictive power of these methods for a preliminary evaluation of potential cooling mechanisms in heteronuclear open shell systems which offer the experimentalist an electric as well as a magnetic handle for manipulation. The series of $X$-Sr molecules, with $X$ = Li, Na, K and Rb, has been chosen for a direct comparison. Quantum degenerate mixtures of Rb and Sr have already been produced,\footnote{B. Pasquiou, A. Bayerle, S. M. Tzanova, S. Stellmer, J. Szczepkowski, M. Parigger, R. Grimm, and F. Schreck, Phys. Rev. A, 2013, 88, 023601} making this combination very promising for the production of ultracold molecules

SPECTROSCOPIC ACCURACY IN QUANTUM CHEMISTRY: A BENCHMARK STUDY ON Na3

Modern techniques of quantum chemistry allow the prediction of molecular properties to good accuracy, provided the systems are small and their electronic structure is not too complex. For most users of common program packages, `chemical' accuracy in the order of a few kJ/mol for relative energies between different geometries is sufficient. The demands of molecular spectroscopists are typically much more stringent, and often include a detailed topographical survey of multi-dimensional potential energy surfaces with an accuracy in the range of wavenumbers. In a benchmark study of current predictive capabilities we pick the slightly sophisticated, but conceptually simple and well studied case of the Na$_3$ ground state, and present a thorough investigation of the interplay between Jahn-Teller-, spin-orbit-, rovibrational- and hyperfine-interactions based only on ab initio calculations. The necessary parameters for the effective Hamiltonian are derived from the potential energy surface of the 1$^{2}$E$^{prime{}}$ ground state and from spin density evaluations at selected geometries, without any fitting adjustments to experimental data. We compare our results to highly resolved microwave spectra.footnote{L. H. Coudert, W. E. Ernst and O. Golonzka, J. Chem. Phys. 117, 7102�7116 (2002)

A systematic study on Pt based, subnanometer-sized alloy cluster catalysts for alkane dehydrogenation: effects of intermetallic interaction

Platinum-based bimetallic nanoparticles are analyzed by the application of density functional theory to a series of tetrahedral Pt3X cluster models, with element X taken from the P-block, preferably group 14, or from the D-block around group 10. Almost identical cluster geometries allow a systematic investigation of electronic effects induced by different elements X. Choosing the propane-to-propene conversion as the desired dehydrogenation reaction, we provide estimates for the activity and selectivity of the various catalysts based on transition state theory. No significant Brønsted-Evans-Polanyi-relation could be found for the given reaction. A new descriptor, derived from an energy decomposition analysis, captures the effect of element X on the rate-determining step of the first hydrogen abstraction. Higher activities than obtained for pure Pt4 clusters are predicted for Pt alloys containing Ir, Sn, Ge and Si, with Pt3Ir showing particularly high selectivity