The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Sebastiaan Y T Van De Meerakker - One of the best experts on this subject based on the ideXlab platform.
-
high resolution imaging of Molecular Collisions using a zeeman decelerator
Journal of Chemical Physics, 2020Co-Authors: Vikram Plomp, Zhi Gao, Theo Cremers, Matthieu Besemer, Sebastiaan Y T Van De MeerakkerAbstract:We present the first crossed beam scattering experiment using a Zeeman decelerated Molecular beam. The narrow velocity spreads of Zeeman decelerated NO (X2Π3/2, j = 3/2) radicals result in high-resolution scattering images, thereby fully resolving quantum diffraction oscillations in the angular scattering distribution for inelastic NO–Ne Collisions and product-pair correlations in the radial scattering distribution for inelastic NO–O2 Collisions. These measurements demonstrate similar resolution and sensitivity as in experiments using Stark decelerators, opening up possibilities for controlled and low-energy scattering experiments using chemically relevant species such as H and O atoms, O2 molecules, or NH radicals.
-
unraveling cold Molecular Collisions stark decelerators in crossed beam experiments
ChemPhysChem, 2016Co-Authors: Jolijn Onvlee, Sjoerd N. Vogels, Sebastiaan Y T Van De MeerakkerAbstract:In the last two decades, enormous progress has been made in the manipulation of Molecular beams. In particular, Molecular decelerators have been developed with which advanced control over neutral molecules in a beam can be achieved. By using arrays of inhomogeneous and time-varying electric (or magnetic) fields, bunches of molecules can be produced with a tunable velocity, narrow velocity spreads, and almost perfect quantum-state purity. These monochromatic or "tamed" Molecular beams are ideally suited to be used in crossed-Molecular-beam scattering experiments. Here, we review the first generation of these "cold and controlled" scattering experiments that have been conducted in the last decade and discuss the prospects for this emerging field of research in the years to come.
-
imaging resonances in low energy no he inelastic Collisions
Science, 2015Co-Authors: Sjoerd N. Vogels, Jolijn Onvlee, Ad Van Der Avoird, Gerrit C. Groenenboom, Simon Chefdeville, Sebastiaan Y T Van De MeerakkerAbstract:In Molecular Collisions, resonances occur at specific energies at which the colliding particles temporarily form quasibound complexes, resulting in rapid variations in the energy dependence of scattering cross sections. Experimentally, it has proven challenging to observe such scattering resonances, especially in differential cross sections. We report the observation of resonance fingerprints in the state-to-state differential cross sections for inelastic NO-He Collisions in the 13 to 19 centimeter–1 energy range with 0.3 centimeter–1 resolution. The observed structures were in excellent agreement with quantum scattering calculations. They were analyzed by separating the resonance contributions to the differential cross sections from the background through a partitioning of the multichannel scattering matrix. This revealed the partial-wave composition of the resonances and their evolution during the collision.
-
high resolution imaging of velocity controlled Molecular Collisions using counterpropagating beams
Physical Review Letters, 2014Co-Authors: Sjoerd N. Vogels, Jolijn Onvlee, Ad Van Der Avoird, Gerrit C. Groenenboom, Alexander Von Zastrow, Sebastiaan Y T Van De MeerakkerAbstract:We present ultrahigh-resolution measurements of state-to-state inelastic differential cross sections for NO-Ne and NO-Ar Collisions, obtained by combining the Stark deceleration and velocity map imaging techniques. We show that for counterpropagating crossed beam geometries, the effect of the velocity spreads of the reagent beams on the angular resolution of the images is minimized. Furthermore, the counterpropagating geometry results in images that are symmetric with respect to the relative velocity vector. This allows for the use of inverse Abel transformation methods that enhance the resolution further. State-resolved diffraction oscillations in the differential cross sections are measured with an angular resolution approaching 0.3°. Distinct structures observed in the cross sections gauge the quality of recent ab initio potential energy surfaces for NO–rare-gas atom Collisions with unprecedented precision.
-
Taming Molecular Collisions using electric and magnetic fields
Chemical Society reviews, 2014Co-Authors: Mark Brouard, David H. Parker, Sebastiaan Y T Van De MeerakkerAbstract:The motion of molecules that possess a permanent electric or magnetic dipole moment can be manipulated using electric or magnetic fields. Various devices have been developed over the last few decades to deflect or focus molecules, to orient them in space, and to decelerate or accelerate them. These precisely controlled molecules are ideal starting points for scattering experiments that reveal the quantum mechanical nature of Molecular interactions. In this Tutorial Review, we present an overview of the various manipulation tools, discuss how they can be used to advantage in Molecular beam scattering experiments, and review recent progress in this field. We describe a selection of benchmark experiments that illustrate the unique possibilities that are available nowadays to study Molecular Collisions under controlled conditions.
Timur V. Tscherbul - One of the best experts on this subject based on the ideXlab platform.
-
complete quantum coherent control of ultracold Molecular Collisions
Physical Review Letters, 2021Co-Authors: Adrien Devolder, Paul Brumer, Timur V. TscherbulAbstract:We show that quantum interference-based coherent control is a highly efficient tool for tuning ultracold Molecular collision dynamics that is free from the limitations of commonly used methods that rely on external electromagnetic fields. By varying the relative populations and phases of initial coherent superpositions of degenerate Molecular states, we demonstrate complete coherent control over integral scattering cross sections in the ultracold $s$-wave regime of both the initial and final collision channels. The proposed control methodology is applied to ultracold ${\mathrm{O}}_{2}+{\mathrm{O}}_{2}$ Collisions, showing extensive control over $s$-wave spin-exchange cross sections and product branching ratios over many orders of magnitude.
-
full dimensional quantum scattering calculations on ultracold atom molecule Collisions in magnetic fields the role of Molecular vibrations
arXiv: Atomic Physics, 2020Co-Authors: Masato Morita, Jacek Klos, Timur V. TscherbulAbstract:Rigorous quantum scattering calculations on ultracold Molecular Collisions in external fields present an outstanding computational problem due to strongly anisotropic atom-molecule interactions that depend on the relative orientation of the collision partners, as well as on their vibrational degrees of freedom. Here, we present the first numerically exact three-dimensional quantum scattering calculations on strongly anisotropic atom-molecule (Li+CaH) Collisions in an external magnetic field based on the parity-adapted total angular momentum representation and a new three-dimensional potential energy surface (PES) for the triplet Li-CaH collision complex using the unrestricted coupled cluster method with single, double and perturbative triple excitations [UCCSD(T)] and a large quadruple-zeta type basis set. We find that while the full three-dimensional treatment is necessary for the accurate description of Li ($M_S=1/2$)+CaH ($v=0,N=0,M_S=1/2$) Collisions as a function of magnetic field, the magnetic resonance density and statistical properties of spin-polarized atom-molecule Collisions are not strongly affected by vibrational degrees of freedom, justifying the rigid-rotor approximation used in previous calculations. We observe rapid, field-insensitive vibrational quenching in ultracold Li ($M_S=1/2$)+CaH ($v=1,N=0, M_S=1/2$) Collisions, leading to efficient collisional cooling of CaH vibrations.
-
universal probability distributions of scattering observables in ultracold Molecular Collisions
Physical Review Letters, 2019Co-Authors: Masato Morita, Roman V. Krems, Timur V. TscherbulAbstract:Currently, quantum dynamics theory cannot be used for quantitative predictions of Molecular scattering observables at low temperatures because of two problems. The first problem is the extreme sensitivity of the low-temperature observables to details of potential energy surfaces (PESs) parametrizing the nuclear Schr\"odinger equation. The second problem is the large size of the basis sets required for the numerical integration of the Schr\"odinger equation for strongly interacting molecules in the presence of fields, which precludes the application of rigorous quantum theory to all but a few atom-molecule systems. Here, we show that, if the scattering problem is formulated as a probabilistic prediction, quantum theory can provide reliable results with exponentially reduced numerical effort. Specifically, we show that the probability distributions that an observable is in a certain range of values can be obtained by averaging the results of scattering calculations with much smaller basis sets than required for calculations of individual scattering cross sections. Moreover, we show that such distributions do not rely on the precise knowledge of the PES. This opens the possibility of making probabilistic predictions of experimentally relevant observables for a wide variety of Molecular systems, currently considered out of reach of quantum dynamics theory. We demonstrate the approach by computing the probability for elastic scattering of CaH and SrOH molecules by Li atoms and SrF molecules by Rb atoms.
-
Molecular Collisions and reactive scattering in external fields are field induced couplings important at short range
Journal of Chemical Physics, 2017Co-Authors: D Vieira, Roman V. Krems, Timur V. TscherbulAbstract:We use accurate quantum scattering calculations to elucidate the role of short-range molecule-field interactions in atom-molecule inelastic Collisions and abstraction chemical reactions at low temperatures. We consider two examples: elastic and inelastic scattering of NH(Σ3) molecules with Mg(S1) atoms in a magnetic field; reactive scattering LiF + H → Li + HF in an electric field. Our calculations suggest that, for non-reactive collision systems and abstraction chemical reactions, the molecule-field interactions cannot generally be neglected at short range because the atom-molecule potential passes through zero at short range. An important exception occurs for Zeeman transitions in atom-molecule Collisions at magnetic fields ≲1000 G, for which the molecule-field couplings need only be included at large ρ outside the range of the atom-molecule interaction. Our results highlight the importance of an accurate description of ρ-dependent molecule-field interactions in quantum scattering calculations on Molecular Collisions and chemical reactions at low temperatures.
-
Quantum theory of Molecular Collisions in a magnetic field: Efficient calculations based on the total angular momentum representation
The Journal of chemical physics, 2010Co-Authors: Timur V. Tscherbul, Alexander DalgarnoAbstract:An efficient method is presented for rigorous quantum calculations of atom-molecule and molecule-molecule Collisions in a magnetic field. The method is based on the expansion of the wave function of the collision complex in basis functions with well-defined total angular momentum in the body-fixed coordinate frame. We outline the general theory of the method for Collisions of diatomic molecules in the Σ2 and Σ3 electronic states with structureless atoms and with unlike Σ2 and Σ3 molecules. The cross sections for elastic scattering and Zeeman relaxation in low-temperature Collisions of CaH(Σ+2) and NH(Σ−3) molecules with H3e atoms converge quickly with respect to the number of total angular momentum states included in the basis set, leading to a dramatic (>10-fold) enhancement in computational efficiency compared to the previously used methods [A. Volpi and J. L. Bohn, Phys. Rev. A 65, 052712 (2002); R. V. Krems and A. Dalgarno, J. Chem. Phys. 120, 2296 (2004)]. Our approach is thus well suited for theoret...
Naduvalath Balakrishnan - One of the best experts on this subject based on the ideXlab platform.
-
stereodynamics of rotationally inelastic scattering in cold he hd Collisions
Journal of Chemical Physics, 2020Co-Authors: Masato Morita, Naduvalath BalakrishnanAbstract:Stereodynamics of cold Collisions has become a fertile ground for sensitive probe of Molecular Collisions and control of the collision outcome. A benchmark system for stereodynamic control of rotational transition is He + HD. This system was recently probed experimentally by Perreault et al. by examining quenching from j = 2 to j′ = 0 state in the v = 1 vibrational manifold of HD. Here, through explicit quantum scattering calculations on a highly accurate ab initio interaction potential for He + H2, we reveal how a combination of two shape resonances arising from l = 1 and l = 2 partial waves controls the stereodynamic outcome rather than a single l = 2 partial wave attributed in the experiment. Furthermore, for collision energies below 0.5 cm−1, it is shown that stereodynamic preference for the integral cross section follows a simple universal trend.
-
Stereodynamic control of overlapping resonances in cold Molecular Collisions
Physical Review Research, 2020Co-Authors: Masato Morita, Qian Yao, Changjian Xie, Hua Guo, Naduvalath BalakrishnanAbstract:This paper reports the possibility of robust stereo-dynamic control of rotational quenching in cold Molecular Collisions. By controlling the orientation and alignment of the molecule before collision, the authors show control of multiple peaks due to resonances associated with disparate partial waves.
-
Controlling rotational quenching rates in cold Molecular Collisions
The Journal of chemical physics, 2019Co-Authors: J. F. E. Croft, Naduvalath BalakrishnanAbstract:The relative orientation and alignment of colliding molecules plays a key role in determining the rates of chemical processes. Here, we examine in detail a prototypical example: rotational quenching of HD in cold Collisions with H2. We show that the rotational quenching rate from j = 2 → 0, in the v = 1 vibrational level, can be maximized by aligning the HD along the collision axis and can be minimized by aligning the HD at the so called magic angle. This follows from quite general helicity considerations and suggests that quenching rates for other similar systems can also be controlled in this manner.
Jeremy M. Hutson - One of the best experts on this subject based on the ideXlab platform.
-
Time delays in ultracold atomic and Molecular Collisions
Physical Review Research, 2019Co-Authors: Matthew D. Frye, Jeremy M. HutsonAbstract:We study the behavior of the Eisenbud-Wigner collisional time delay around Feshbach resonances in cold and ultracold atomic and Molecular Collisions. We carry out coupled-channel scattering calculations on ultracold Rb and Cs Collisions. In the low-energy limit, the time delay is proportional to the scattering length and so exhibits a pole as a function of applied field. At high energy, it exhibits a Lorentzian peak as a function of either energy or field. For narrow resonances, the crossover between these two regimes occurs at an energy proportional to the square of the resonance strength parameter sres. For wider resonances, the behavior is more complicated and we present an analysis in terms of multichannel quantum defect theory.
-
molscat a program for non reactive quantum scattering calculations on atomic and Molecular Collisions
Computer Physics Communications, 2019Co-Authors: Jeremy M. Hutson, Ruth Le C SueurAbstract:molscat is a general-purpose program for quantum-mechanical calculations on nonreactive atom– atom, atom–molecule and molecule–molecule Collisions. It constructs the coupled-channel equations of atomic and Molecular scattering theory, and solves them by propagating the wavefunction or log- derivative matrix outwards from short range to the asymptotic region at long range. It then applies scattering boundary conditions to extract the scattering matrix (S matrix). Built-in coupling cases include atom + rigid linear molecule, atom + vibrating diatom, atom + rigid symmetric top, atom + asymmetricorsphericaltop,rigiddiatom+rigiddiatom,rigiddiatom+asymmetrictop,anddiffractive scattering of an atom from a crystal surface. Interaction potentials may be specified either in program input (for simple cases) or with user-supplied routines. For the built-in coupling cases, molscat can loop over total angular momentum (partial wave) and total parity to calculate elastic and inelastic integral cross sections and spectroscopic line-shape cross sections. Post-processors are available to calculate differential cross sections, transport, relaxation and Senftleben–Beenakker cross sections, and tofittheparametersofscatteringresonances. molscat alsoprovidesaninterfaceforplug-inroutinesto specify coupling cases (Hamiltonians and basis sets) that are not built in; plug-in routines are supplied to handle Collisions of a pair of alkali-metal atoms with hyperfine structure in an applied magnetic field. For low-energy scattering, molscat can calculate scattering lengths and effective ranges and can locateandcharacterisescatteringresonancesasafunctionofanexternalvariablesuchasthemagnetic field.
-
Time delays in ultracold atomic and Molecular Collisions.
arXiv: Atomic Physics, 2019Co-Authors: Matthew D. Frye, Jeremy M. HutsonAbstract:We study the behavior of the Eisenbud-Wigner collisional time delay around Feshbach resonances in cold and ultracold atomic and Molecular Collisions. We carry out coupled-channels scattering calculations on ultracold Rb and Cs Collisions. In the low-energy limit, the time delay is proportional to the scattering length, so exhibits a pole as a function of applied field. At high energy, it exhibits a Lorentzian peak as a function of either energy or field. For narrow resonances, the crossover between these two regimes occurs at an energy proportional to the square of the resonance strength parameter $s_\textrm{res}$. For wider resonances, the behavior is more complicated and we present an analysis in terms of multichannel quantum defect theory.
-
user manual for molscat bound and field version 2020 0 programs for quantum scattering properties and bound states of interacting pairs of atoms and molecules
arXiv: Chemical Physics, 2019Co-Authors: Jeremy M. Hutson, Ruth Le C SueurAbstract:MOLSCAT is a general-purpose package for performing non-reactive quantum scattering calculations for atomic and Molecular Collisions using coupled-channel methods. Simple atom-molecule and molecule-molecule collision types are coded internally and additional ones may be handled with plug-in routines. Plug-in routines may include external magnetic, electric or photon fields (and combinations of them). Simple interaction potentials are coded internally and more complicated ones may be handled with plug-in routines. BOUND is a general-purpose package for performing calculations of bound-state energies in weakly bound atomic and Molecular systems using coupled-channel methods. It solves the same sets of coupled equations as \MOLSCAT, and can use the same plug-in routines if desired, but with different boundary conditions. FIELD is a development of BOUND that locates external fields at which a bound state exists with a specified energy. One important use is to locate the positions of magnetically tunable Feshbach resonance positions in ultracold Collisions. Versions of these programs before version 2019.0 were released separately. However, there is a significant degree of overlap between their internal structures and usage specifications. This manual therefore describes all three, with careful identification of parts that are specific to one or two of the programs.
-
cold atomic and Molecular Collisions approaching the universal loss regime
New Journal of Physics, 2015Co-Authors: Matthew D. Frye, Paul S Julienne, Jeremy M. HutsonAbstract:We investigate the behaviour of single-channel theoretical models of cold and ultracold Collisions that take account of inelastic and reactive processes using a single parameter to represent short-range loss. We present plots of the resulting energy-dependence of elastic and inelastic or reactive cross-sections over the full parameter space of loss parameters and short-range phase shifts. We then test the single-channel model by comparing it with the results of coupled-channel calculations of rotationally inelastic Collisions between LiH molecules and Li atoms. We find that the range of cross-sections predicted by the single-channel model becomes increasingly accurate as the initial LiH rotational quantum number increases, with a corresponding increase in the number of open loss channels. The results suggest that coupled-channel calculations at very low energy (in the s-wave regime) could in some cases be used to estimate a loss parameter and then to predict the range of possible loss rates at higher energy, without the need for explicit coupled-channel calculations for higher partial waves.
Masato Morita - One of the best experts on this subject based on the ideXlab platform.
-
stereodynamics of rotationally inelastic scattering in cold he hd Collisions
Journal of Chemical Physics, 2020Co-Authors: Masato Morita, Naduvalath BalakrishnanAbstract:Stereodynamics of cold Collisions has become a fertile ground for sensitive probe of Molecular Collisions and control of the collision outcome. A benchmark system for stereodynamic control of rotational transition is He + HD. This system was recently probed experimentally by Perreault et al. by examining quenching from j = 2 to j′ = 0 state in the v = 1 vibrational manifold of HD. Here, through explicit quantum scattering calculations on a highly accurate ab initio interaction potential for He + H2, we reveal how a combination of two shape resonances arising from l = 1 and l = 2 partial waves controls the stereodynamic outcome rather than a single l = 2 partial wave attributed in the experiment. Furthermore, for collision energies below 0.5 cm−1, it is shown that stereodynamic preference for the integral cross section follows a simple universal trend.
-
Stereodynamic control of overlapping resonances in cold Molecular Collisions
Physical Review Research, 2020Co-Authors: Masato Morita, Qian Yao, Changjian Xie, Hua Guo, Naduvalath BalakrishnanAbstract:This paper reports the possibility of robust stereo-dynamic control of rotational quenching in cold Molecular Collisions. By controlling the orientation and alignment of the molecule before collision, the authors show control of multiple peaks due to resonances associated with disparate partial waves.
-
stereodynamic control of overlapping resonances in cold Molecular Collisions
arXiv: Chemical Physics, 2020Co-Authors: Masato Morita, Qian Yao, Changjian Xie, Hua Guo, N BalakrishnanAbstract:Stereodynamic control of resonant Molecular Collisions has emerged as a new frontier in cold molecule research. Recent experimental studies have focused on weakly interacting Molecular systems such as HD Collisions with H$_2$, D$_2$ and He. We report here the possibility of such control in strongly interacting systems taking rotational relaxation in cold Collisions of HCl and H$_2$. Using explicit quantum scattering calculations in full six dimensions it is shown that robust control of the collision dynamics is possible even when multiple (overlapping) shape-resonances coexist in a narrow energy range, indicating that cold stereochemistry offers great promise for many molecules beyond simple systems. We demonstrate a striking case where two prominent peaks in overlapping resonances are switched-off simultaneously by suitable alignment of the HCl molecule.
-
full dimensional quantum scattering calculations on ultracold atom molecule Collisions in magnetic fields the role of Molecular vibrations
arXiv: Atomic Physics, 2020Co-Authors: Masato Morita, Jacek Klos, Timur V. TscherbulAbstract:Rigorous quantum scattering calculations on ultracold Molecular Collisions in external fields present an outstanding computational problem due to strongly anisotropic atom-molecule interactions that depend on the relative orientation of the collision partners, as well as on their vibrational degrees of freedom. Here, we present the first numerically exact three-dimensional quantum scattering calculations on strongly anisotropic atom-molecule (Li+CaH) Collisions in an external magnetic field based on the parity-adapted total angular momentum representation and a new three-dimensional potential energy surface (PES) for the triplet Li-CaH collision complex using the unrestricted coupled cluster method with single, double and perturbative triple excitations [UCCSD(T)] and a large quadruple-zeta type basis set. We find that while the full three-dimensional treatment is necessary for the accurate description of Li ($M_S=1/2$)+CaH ($v=0,N=0,M_S=1/2$) Collisions as a function of magnetic field, the magnetic resonance density and statistical properties of spin-polarized atom-molecule Collisions are not strongly affected by vibrational degrees of freedom, justifying the rigid-rotor approximation used in previous calculations. We observe rapid, field-insensitive vibrational quenching in ultracold Li ($M_S=1/2$)+CaH ($v=1,N=0, M_S=1/2$) Collisions, leading to efficient collisional cooling of CaH vibrations.
-
universal probability distributions of scattering observables in ultracold Molecular Collisions
Physical Review Letters, 2019Co-Authors: Masato Morita, Roman V. Krems, Timur V. TscherbulAbstract:Currently, quantum dynamics theory cannot be used for quantitative predictions of Molecular scattering observables at low temperatures because of two problems. The first problem is the extreme sensitivity of the low-temperature observables to details of potential energy surfaces (PESs) parametrizing the nuclear Schr\"odinger equation. The second problem is the large size of the basis sets required for the numerical integration of the Schr\"odinger equation for strongly interacting molecules in the presence of fields, which precludes the application of rigorous quantum theory to all but a few atom-molecule systems. Here, we show that, if the scattering problem is formulated as a probabilistic prediction, quantum theory can provide reliable results with exponentially reduced numerical effort. Specifically, we show that the probability distributions that an observable is in a certain range of values can be obtained by averaging the results of scattering calculations with much smaller basis sets than required for calculations of individual scattering cross sections. Moreover, we show that such distributions do not rely on the precise knowledge of the PES. This opens the possibility of making probabilistic predictions of experimentally relevant observables for a wide variety of Molecular systems, currently considered out of reach of quantum dynamics theory. We demonstrate the approach by computing the probability for elastic scattering of CaH and SrOH molecules by Li atoms and SrF molecules by Rb atoms.