Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Controlling Rotational Quenching Rates in Cold Molecular Collisions

Croft, James F.E., Naduvalath, Balakrishnan

Published Apr 23, 2019• 5 citations
OpenAlex

Abstract

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.

Related papers

Stereodynamical Control of a Quantum Scattering Resonance in Cold Molecular Collisions

Pablo G. Jambrina, James F. E. Croft, Hua Guo +3 more

Cold collisions of light molecules are often dominated by a single partial wave resonance. For the rotational quenching of HD (v=1, j=2) by collisions with ground state para-H_{2}, the process is dominated by a single L=2 partial wave resonance centered around 0.1 K. Here, we show that this resonance can be switched on or off simply by appropriate alignment of the HD rotational angular momentum relative to the initial velocity vector, thereby enabling complete control of the collision outcome.

arXiv:1905.04765•Physical Review Letters•Jul 26, 2019•59 citations

Stereodynamic control of overlapping resonances in cold molecular collisions

Masato Morita, Qian Yao, Changjian Xie +2 more

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.

arXiv:2005.06129•Physical Review Research•Jul 17, 2020•26 citations

Quenching of rotationally excited CO in cold and ultracold collisions with H, He and H2

Benhui Yang, Hemamali Perera, N. Balakrishnan +2 more

The study of molecular inelastic collision processes at cold and ultracold temperatures is of considerable interest as schemes are currently being developed to efficiently cool and trap neutral polar molecules. In this work, quantum-mechanical scattering calculations are presented for the quenching of rotationally excited CO due to collisions with H, He and H 2 for collision energies between 10 −5 and 10 cm −1 . The calculations were performed using the close-coupling approach and the coupled-states approximation. Cross sections for the quenching of the j = 1–10, 20, 30 and 40 levels of CO are presented and mechanism and trends of energy transfer in these systems are discussed.

Journal of Physics B Atomic Molecular and Optical Physics•Sep 25, 2006•20 citations

Quantum-Controlled Collisions of H2 Molecules

Nandini Mukherjee

The amount of information that can be obtained from a scattering experiment depends upon the precision with which the quantum states are defined in the incoming channel. By precisely defining the incoming states and measuring the outgoing states in a scattering experiment, we set up the boundary condition for experimentally solving the Schrödinger equation. In this Perspective we discuss cold inelastic scattering experiments using the most theoretically tractable H 2 and its isotopologues as the target. We prepare the target in a precisely defined rovibrational ( v, j, m ) quantum state using a special coherent optical technique called the Stark-induced adiabatic Raman passage (SARP). v and j represent the quantum numbers of the vibrational and rotational energy levels, and m refers to the projection of the rotational angular momentum vector j on a suitable quantization axis in the laboratory frame. Selection of the m quantum numbers defines the alignment of the molecular frame, which is necessary to probe the anisotropic interactions. For us to achieve the collision temperature in the range of a few degrees Kelvin, we co-expand the colliding partners in a mixed supersonic beam that is collimated to define a direction for the collision velocity. When the bond axis is aligned with respect to a well-defined collision velocity, SARP achieves stereodynamic control at the quantum scale. Through various examples of rotationally inelastic cold scattering experiments, we show how SARP coherently controls the dynamics of anisotropic interactions by preparing quantum superpositions of the orientational m states within a single rovibrational ( v, j ) energy state. A partial wave analysis, which has been developed for the cold scattering experiments, shows dominance of a resonant orbital that leaves its mark in the scattering angular distribution. These highly controlled cold collision experiments at the single partial wave limit allow the most direct comparison with the results of theoretical computations, necessary for accurate modeling of the molecular interaction potential.

The Journal of Physical Chemistry A•Jan 5, 2023•22 citations

Stereodynamics of ultracold rotationally inelastic collisions

Masato Morita, N. Balakrishnan

, and He near 1 K have revealed strong stereodynamic preference stemming from isolated shape resonances. So far, the experiments and subsequent theoretical analyses have considered the initial HD rotational state in an orientation specified by the projection quantum number m or a coherent superposition of different m states. However, it is known that such stereodynamic control is generally not effective in the ultracold energy regime due to the dominance of the incoming s-wave (l = 0, partial wave). Here, we provide a detailed analysis of the stereodynamics of rotational quenching of HD by He with both m and m' resolution, where m' refers to the inelastically scattered HD. We show the existence of a significant m dependence in the m'-resolved differential and integral cross sections even in the ultracold s-wave regime with a factor greater than 60 for j = 2 → j' = 1 and a factor greater than 1300 for j = 3 → j' = 2 transitions. In the helicity frame, however, the integral cross section has no initial orientation (k) dependence in the ultracold energy regime, even resolving with respect to the final orientation (k'). The distribution of final rotational state orientations (k') is found to be statistical (uniform), regardless of the initial orientation.

The Journal of Chemical Physics•Nov 11, 2020•23 citations

Vibrational energy transfer in ultracold molecule-molecule collisions

Goulven Quéméner, N. Balakrishnan, Roman V. Krems

We present a rigorous study of vibrational relaxation in $\text{para}\text{\ensuremath{-}}{\mathrm{H}}_{2}+\text{para}\text{\ensuremath{-}}{\mathrm{H}}_{2}$ collisions at cold and ultracold temperatures and identify an efficient mechanism of rovibrational energy transfer. If the colliding molecules are in different rotational and vibrational levels, the internal energy may be transferred between the molecules through an extremely state-selective process involving simultaneous conservation of internal energy and total rotational angular momentum. The same transition in collisions of distinguishable molecules corresponds to the rotational energy transfer from one vibrational state of the colliding molecules to another.

arXiv:0709.3081•Physical Review A•Mar 28, 2008•59 citations
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.
The study of molecular inelastic collision processes at cold and ultracold temperatures is of considerable interest as schemes are currently being developed to efficiently cool and trap neutral polar molecules. In this work, quantum-mechanical scattering calculations are presented for the quenching of rotationally excited CO due to collisions with H, He and H 2 for collision energies between 10 −5 and 10 cm −1 . The calculations were performed using the close-coupling approach and the coupled-states approximation. Cross sections for the quenching of the j = 1–10, 20, 30 and 40 levels of CO are presented and mechanism and trends of energy transfer in these systems are discussed.
The amount of information that can be obtained from a scattering experiment depends upon the precision with which the quantum states are defined in the incoming channel. By precisely defining the incoming states and measuring the outgoing states in a scattering experiment, we set up the boundary condition for experimentally solving the Schrödinger equation. In this Perspective we discuss cold inelastic scattering experiments using the most theoretically tractable H 2 and its isotopologues as the target. We prepare the target in a precisely defined rovibrational ( v, j, m ) quantum state using a special coherent optical technique called the Stark-induced adiabatic Raman passage (SARP). v and j represent the quantum numbers of the vibrational and rotational energy levels, and m refers to the projection of the rotational angular momentum vector j on a suitable quantization axis in the laboratory frame. Selection of the m quantum numbers defines the alignment of the molecular frame, which is necessary to probe the anisotropic interactions. For us to achieve the collision temperature in the range of a few degrees Kelvin, we co-expand the colliding partners in a mixed supersonic beam that is collimated to define a direction for the collision velocity. When the bond axis is aligned with respect to a well-defined collision velocity, SARP achieves stereodynamic control at the quantum scale. Through various examples of rotationally inelastic cold scattering experiments, we show how SARP coherently controls the dynamics of anisotropic interactions by preparing quantum superpositions of the orientational m states within a single rovibrational ( v, j ) energy state. A partial wave analysis, which has been developed for the cold scattering experiments, shows dominance of a resonant orbital that leaves its mark in the scattering angular distribution. These highly controlled cold collision experiments at the single partial wave limit allow the most direct comparison with the results of theoretical computations, necessary for accurate modeling of the molecular interaction potential.
, and He near 1 K have revealed strong stereodynamic preference stemming from isolated shape resonances. So far, the experiments and subsequent theoretical analyses have considered the initial HD rotational state in an orientation specified by the projection quantum number m or a coherent superposition of different m states. However, it is known that such stereodynamic control is generally not effective in the ultracold energy regime due to the dominance of the incoming s-wave (l = 0, partial wave). Here, we provide a detailed analysis of the stereodynamics of rotational quenching of HD by He with both m and m' resolution, where m' refers to the inelastically scattered HD. We show the existence of a significant m dependence in the m'-resolved differential and integral cross sections even in the ultracold s-wave regime with a factor greater than 60 for j = 2 → j' = 1 and a factor greater than 1300 for j = 3 → j' = 2 transitions. In the helicity frame, however, the integral cross section has no initial orientation (k) dependence in the ultracold energy regime, even resolving with respect to the final orientation (k'). The distribution of final rotational state orientations (k') is found to be statistical (uniform), regardless of the initial orientation.
We present a rigorous study of vibrational relaxation in $\text{para}\text{\ensuremath{-}}{\mathrm{H}}_{2}+\text{para}\text{\ensuremath{-}}{\mathrm{H}}_{2}$ collisions at cold and ultracold temperatures and identify an efficient mechanism of rovibrational energy transfer. If the colliding molecules are in different rotational and vibrational levels, the internal energy may be transferred between the molecules through an extremely state-selective process involving simultaneous conservation of internal energy and total rotational angular momentum. The same transition in collisions of distinguishable molecules corresponds to the rotational energy transfer from one vibrational state of the colliding molecules to another.