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

Physical Review A

Near-zero-energy electron attachment to S F 6 using Rydberg excitation and two-color resonance-enhanced multiphoton ionization of NO

Irina Jana, Eric James Smoll, Jonathan H. Frank, David W. Chandler

Published Feb 20, 2025• 3 citations
Publisher

Abstract

We report the formation of $\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}$ in a molecular beam containing coexpanded NO and $\mathrm{S}{\mathrm{F}}_{6}$ by direct electron transfer from laser-excited Rydberg states of NO, and electron attachment from ultracold plasma induced by Penning ionization or photoionization of NO. At short times of up to 2 \textmu{}s after laser excitation, we find that the dominant pathway for near-zero-energy electron attachment to $\mathrm{S}{\mathrm{F}}_{6}$ molecules forming $\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}$ ions is from Rydberg electron transfer from excited Rydberg states, within a few $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ of the Rydberg limit. $\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}$ ion production occurs by electron transfer from NO Rydberg states with a principal quantum number $n\ensuremath{\ge}165$. At this principal quantum number threshold, the Rydberg reaction range is \ensuremath{\sim}15 \textmu{}m. For lower-lying Rydberg states of NO, no $\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}$ ions are detected despite the efficiency of $\mathrm{S}{\mathrm{F}}_{6}$ as an electron scavenger of weakly bound electrons. We hypothesize that $\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}$ anions formed in closer proximity to a $\mathrm{N}{\mathrm{O}}^{+}$ cation core may undergo efficient back-electron transfer.

DOI
10.1103/physreva.111.023114

Related papers

On the formation and decay of a molecular ultracold plasma

Nicolas Saquet, J. P. Morrison, Markus Schulz-Weiling +4 more

Double-resonant photoexcitation of nitric oxide in a molecular beam creates a dense ensemble of 50f(2) Rydberg states, which evolves to form a plasma of free electrons trapped in the potential well of an NO + space charge. The plasma travels at the velocity of the molecular beam and, on passing through a grounded grid, yields an electron time-of-flight signal that gauges the plasma size and quantity of trapped electrons. This plasma expands at a rate that fits with an electron temperature as low as 5 K, colder than typically observed for atomic ultracold plasmas. The recombination of molecular NO + cations with electrons forms neutral molecules excited by more than twice the energy of the NO chemical bond, and the question arises whether neutral fragmentation plays a role in shaping the redistribution of energy and particle density that directs the short-time evolution from Rydberg gas to plasma. To explore this question, we adapt a coupled rate-equations model established for atomic ultracold plasmas to describe the energy-grained avalanche of electron–Rydberg and electron–ion collisions in our system. Adding channels of Rydberg predissociation and two-body, electron–cation dissociative recombination to the atomic formalism, we investigate the kinetics by which this relaxation distributes particle density and energy over Rydberg states, free electrons and neutral fragments. The results of this investigation point to conditions under which such processes can effect the steady-state temperature of plasma electrons.

arXiv:1103.0053•Journal of Physics B Atomic Molecular and Optical Physics•Sep 14, 2011•27 citations

Evolution from a Molecular Rydberg Gas to an Ultracold Plasma in a Seeded Supersonic Expansion of NO

J. P. Morrison, Chris Rennick, James S. Keller +1 more

We report the spontaneous formation of a plasma from a gas of cold Rydberg molecules. Double-resonant laser excitation promotes nitric oxide, cooled to 1 K in a seeded supersonic molecular beam, to single Rydberg states extending as deep as $80\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ below the lowest ionization threshold. The density of excited molecules in the illuminated volume approaches $1\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$. This population evolves to produce free electrons and a durable cold plasma of electrons and intact ${\mathrm{NO}}^{+}$ ions.

arXiv:0804.1986•Physical Review Letters•Nov 14, 2008•99 citations

A Study of Heavy-Rydberg Ion-Pair Formation through Rydberg-Atom-Molecule Collisions

Sitti Buathong

Thermal collisions between potassium Rydberg atoms with intermediate values of quantum number n and target molecules that capture free low-energy electrons are investigated. The velocity, binding energy, and angular distributions of heavy-Rydberg ion-pair states formed through such collisions are measured. The experimental data are analyzed with the aid of semiclassical Monte Carlo simulations to investigate the dynamics of electron attachment to a variety of target species. Multiple reaction channels involving short- and long-lived intermediates are seen for electron capture by 1,1,1-C2Cl3F3 and CBrCl3 (where dissociation of CBrCl3 intermediates involves production of Br- and Cl- ions). Electron attachment to BrCN produces long-lived BrCN-* intermediates whose dissociation results in the creation of rotationally-hot CN- anions. Electron capture by Fe(CO)5 leads to formation of Fe(CO)5-* intermediates which can fragment producing Fe(CO)4- anions, either directly or after partial redistribution of the excess energy within the intermediate has occurred. Electron transfer in Rydberg atom collisions with C2Cl4 provide no evidence of formation of long-lived C2Cl4 ions, only Cl- ions are seen. Moreover, strong Rydberg atom scattering is observed following collisions of K(12p) Rydberg states with CH3NO2. This finding is consistent with a theory which predicts that collisions between Rydberg atoms with intermediate values of n and polar molecules can lead to strong resonant quenching of Rydberg states, i.e., n and l changing, through formation of short-lived K+...CH3NO2- ion-pair states. Finally, the improvements in sensitivity to electron capture reaction dynamics that might be achieved using different Rydberg species and a crossed molecular beam are examined. Simulations are performed to demonstrate that the use of a hyperthermal helium Rydberg atomic beam and a crossed beam of target molecules such as CCl4, BrCN and CF3I can provide new insights into dissociative electron attachment reactions. The calculations show that not only can much detailed information on translational energy release distributions and intermediate lifetimes be obtained, but also on the electron radial probability density distributions in the Rydberg atoms themselves.

•Aug 30, 2018•0 citations

Ionizing collisions of He( n1 P) atoms in a low-Rydberg state with SF6 and NO2 electron-attaching molecules

A. Pesnelle, C. Ronge, M. Perdrix +1 more

The ionization of He atoms, prepared in a well-defined (n=14) $^{1}$P Rydberg state, in collisions with electron-attaching molecules like ${\mathrm{SF}}_{6}$ and ${\mathrm{NO}}_{2}$, is studied in a crossed-beam experiment at thermal energies. The ionization cross section is observed to be large for ${\mathrm{SF}}_{6}$, reaching 4.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ ${\mathrm{cm}}^{2}$, and to be smaller for ${\mathrm{NO}}_{2}$, close to ${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{cm}}^{2}$. The dependence of these two cross sections on the relative velocity of the reactants exhibits a characteristic behavior with a saturation at low velocities, a dependence that is completely different from that obtained with polar molecules. The observation of such a dependence for ${\mathrm{NO}}_{2}$ indicates that, for this molecule, the reaction product is an ion pair, as for ${\mathrm{SF}}_{6}$, and that ionization is not due to rotational energy transfer even though ${\mathrm{NO}}_{2}$ has a dipole moment. This dependence cannot be explained by the ``free-electron model'' usually used in Rydberg-atom--molecule collisions; it clearly shows that the interaction of the molecule with the ion core cannot be neglected.

Physical Review A•Jul 1, 1990•15 citations

Dissociative recombination and the decay of a molecular ultracold plasma

Chris Rennick, Nicolas Saquet, J. P. Morrison +5 more

Double-resonant photoexcitation of nitric oxide in a molecular beam creates a dense ensemble of 51f(2) Rydberg states, which evolves to form a plasma of free electrons trapped in the potential well of an NO + spacecharge. The plasma travels at the velocity of the molecular beam, and, on passing through a grounded grid, yields an electron time-of-flight signal that gauges the plasma size and quantity of trapped electrons. This plasma expands at a rate that fits with an electron temperature as low as 5 K. Dissociative recombination of NO + ions with electrons provides the primary dissipation mechanism for the plasma. We have identified three dissociation pathways, and quantified their relative contributions to the measured rate: Two-body dissociative recombination competes with direct three-body recombination to neutral dissociation products, and with a process in which three-body recombination and electron-impact ionization form an equilibrium population of high-Rydberg states that decays by predissociation. Using available collision-theory rate constants for three-body recombination and ionization, together with quantum mechanical estimates of predissociation rates, we predict that the relaxation of the plasma to a high-Rydberg equilibrium outpaces direct three-body dissociative recombination, and, among second-order processes, the rate of two-body electron-cation dissociative recombination substantially exceeds the rate at which the high-Rydberg equilibrium dissociatively relaxes. The rate constant for dissociative recombination extracted from these data conforms with predictions drawn from theory for isolated electron-ion collisions. Methods based on the dissipation of molecular ultracold plasmas may provide a means for estimating rates of dissociative recombination for a variety of complex molecules.

Journal of Physics Conference Series•Jul 20, 2011•4 citations

Quantum state control of ultracold plasma fission

Markus Schulz-Weiling, Edward R. Grant

Abstract Double-resonant transitions excite nitric oxide in a seeded supersonic molecular beam, yielding a state-selected Rydberg gas that evolves to form an ultracold plasma. This plasma propagates in z with the molecular beam over a variable distance as great as 600 mm to strike an imaging detector, which records the charge distribution in the dimensions, x and y . The laser-crossed molecular beam excitation geometry convolutes an axial Gaussian distribution of NO about z with the Gaussian intensity distribution of the laser beam about x to create an ellipsoidal volume of Rydberg gas. Plasma images provide evidence for the relaxation of this Rydberg gas volume in an electron impact avalanche that breaks the ellipsoidal symmetry in x to form repelling plasma volumes. We find that the energy deposited in the recoil velocity of mass transport, V x depends systematically on the initially selected Rydberg gas principal quantum number, n 0 , and the initial density of the Rydberg gas, ρ 0 . These quantities combine to determine ρ e , the initial density of electrons formed by the prompt Penning ionization of closely spaced pairs of Rydberg molecules. Above a threshold density of Penning electrons, we find that V x depends linearly on ρ e . We argue that this bifurcation occurs as a consequence of the initial geometry of the Rydberg gas. Ambipolar electron expansion accelerates initially formed core ions. Resonant charge transfer redistributes this ion energy to the column of Rydberg molecules on the long axis of the ellipsoid. The equalized velocities in each direction give rise to a ± x streaming motion that concentrates density in opposing plasma volumes, causing the symmetric gas volume to split like a rotating liquid drop. Significantly, these dynamics reduce electron temperature with little decrease in the ion density or increase in the ion temperature. This appears to facilitate the formation of a strongly coupled plasma.

Journal of Physics B Atomic Molecular and Optical Physics•Mar 7, 2016•11 citations
We report the formation of SF6\ensuremath−\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}SF6\ensuremath−​ in a molecular beam containing coexpanded NO and SF6\mathrm{S}{\mathrm{F}}_{6}SF6​ by direct electron transfer from laser-excited Rydberg states of NO, and electron attachment from ultracold plasma induced by Penning ionization or photoionization of NO. At short times of up to 2 \textmu{}s after laser excitation, we find that the dominant pathway for near-zero-energy electron attachment to SF6\mathrm{S}{\mathrm{F}}_{6}SF6​ molecules forming SF6\ensuremath−\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}SF6\ensuremath−​ ions is from Rydberg electron transfer from excited Rydberg states, within a few cm\ensuremath−1\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}cm\ensuremath−1 of the Rydberg limit. SF6\ensuremath−\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}SF6\ensuremath−​ ion production occurs by electron transfer from NO Rydberg states with a principal quantum number n\ensuremath≥165n\ensuremath{\ge}165n\ensuremath≥165. At this principal quantum number threshold, the Rydberg reaction range is \ensuremath{\sim}15 \textmu{}m. For lower-lying Rydberg states of NO, no SF6\ensuremath−\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}SF6\ensuremath−​ ions are detected despite the efficiency of SF6\mathrm{S}{\mathrm{F}}_{6}SF6​ as an electron scavenger of weakly bound electrons. We hypothesize that SF6\ensuremath−\mathrm{S}{\mathrm{F}}_{6}^{\ensuremath{-}}SF6\ensuremath−​ anions formed in closer proximity to a NO+\mathrm{N}{\mathrm{O}}^{+}NO+ cation core may undergo efficient back-electron transfer.
Double-resonant photoexcitation of nitric oxide in a molecular beam creates a dense ensemble of 50f(2) Rydberg states, which evolves to form a plasma of free electrons trapped in the potential well of an NO + space charge. The plasma travels at the velocity of the molecular beam and, on passing through a grounded grid, yields an electron time-of-flight signal that gauges the plasma size and quantity of trapped electrons. This plasma expands at a rate that fits with an electron temperature as low as 5 K, colder than typically observed for atomic ultracold plasmas. The recombination of molecular NO + cations with electrons forms neutral molecules excited by more than twice the energy of the NO chemical bond, and the question arises whether neutral fragmentation plays a role in shaping the redistribution of energy and particle density that directs the short-time evolution from Rydberg gas to plasma. To explore this question, we adapt a coupled rate-equations model established for atomic ultracold plasmas to describe the energy-grained avalanche of electron–Rydberg and electron–ion collisions in our system. Adding channels of Rydberg predissociation and two-body, electron–cation dissociative recombination to the atomic formalism, we investigate the kinetics by which this relaxation distributes particle density and energy over Rydberg states, free electrons and neutral fragments. The results of this investigation point to conditions under which such processes can effect the steady-state temperature of plasma electrons.
We report the spontaneous formation of a plasma from a gas of cold Rydberg molecules. Double-resonant laser excitation promotes nitric oxide, cooled to 1 K in a seeded supersonic molecular beam, to single Rydberg states extending as deep as $80\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ below the lowest ionization threshold. The density of excited molecules in the illuminated volume approaches $1\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$. This population evolves to produce free electrons and a durable cold plasma of electrons and intact NO+{\mathrm{NO}}^{+}NO+ ions.
Thermal collisions between potassium Rydberg atoms with intermediate values of quantum number n and target molecules that capture free low-energy electrons are investigated. The velocity, binding energy, and angular distributions of heavy-Rydberg ion-pair states formed through such collisions are measured. The experimental data are analyzed with the aid of semiclassical Monte Carlo simulations to investigate the dynamics of electron attachment to a variety of target species. Multiple reaction channels involving short- and long-lived intermediates are seen for electron capture by 1,1,1-C2Cl3F3 and CBrCl3 (where dissociation of CBrCl3 intermediates involves production of Br- and Cl- ions). Electron attachment to BrCN produces long-lived BrCN-* intermediates whose dissociation results in the creation of rotationally-hot CN- anions. Electron capture by Fe(CO)5 leads to formation of Fe(CO)5-* intermediates which can fragment producing Fe(CO)4- anions, either directly or after partial redistribution of the excess energy within the intermediate has occurred. Electron transfer in Rydberg atom collisions with C2Cl4 provide no evidence of formation of long-lived C2Cl4 ions, only Cl- ions are seen. Moreover, strong Rydberg atom scattering is observed following collisions of K(12p) Rydberg states with CH3NO2. This finding is consistent with a theory which predicts that collisions between Rydberg atoms with intermediate values of n and polar molecules can lead to strong resonant quenching of Rydberg states, i.e., n and l changing, through formation of short-lived K+...CH3NO2- ion-pair states. Finally, the improvements in sensitivity to electron capture reaction dynamics that might be achieved using different Rydberg species and a crossed molecular beam are examined. Simulations are performed to demonstrate that the use of a hyperthermal helium Rydberg atomic beam and a crossed beam of target molecules such as CCl4, BrCN and CF3I can provide new insights into dissociative electron attachment reactions. The calculations show that not only can much detailed information on translational energy release distributions and intermediate lifetimes be obtained, but also on the electron radial probability density distributions in the Rydberg atoms themselves.
The ionization of He atoms, prepared in a well-defined (n=14) 1^{1}1P Rydberg state, in collisions with electron-attaching molecules like SF6{\mathrm{SF}}_{6}SF6​ and NO2{\mathrm{NO}}_{2}NO2​, is studied in a crossed-beam experiment at thermal energies. The ionization cross section is observed to be large for SF6{\mathrm{SF}}_{6}SF6​, reaching 4.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$ cm2{\mathrm{cm}}^{2}cm2, and to be smaller for NO2{\mathrm{NO}}_{2}NO2​, close to ${10}^{\mathrm{\ensuremath{-}}15}$ cm2{\mathrm{cm}}^{2}cm2. The dependence of these two cross sections on the relative velocity of the reactants exhibits a characteristic behavior with a saturation at low velocities, a dependence that is completely different from that obtained with polar molecules. The observation of such a dependence for NO2{\mathrm{NO}}_{2}NO2​ indicates that, for this molecule, the reaction product is an ion pair, as for SF6{\mathrm{SF}}_{6}SF6​, and that ionization is not due to rotational energy transfer even though NO2{\mathrm{NO}}_{2}NO2​ has a dipole moment. This dependence cannot be explained by the ``free-electron model'' usually used in Rydberg-atom--molecule collisions; it clearly shows that the interaction of the molecule with the ion core cannot be neglected.
Double-resonant photoexcitation of nitric oxide in a molecular beam creates a dense ensemble of 51f(2) Rydberg states, which evolves to form a plasma of free electrons trapped in the potential well of an NO + spacecharge. The plasma travels at the velocity of the molecular beam, and, on passing through a grounded grid, yields an electron time-of-flight signal that gauges the plasma size and quantity of trapped electrons. This plasma expands at a rate that fits with an electron temperature as low as 5 K. Dissociative recombination of NO + ions with electrons provides the primary dissipation mechanism for the plasma. We have identified three dissociation pathways, and quantified their relative contributions to the measured rate: Two-body dissociative recombination competes with direct three-body recombination to neutral dissociation products, and with a process in which three-body recombination and electron-impact ionization form an equilibrium population of high-Rydberg states that decays by predissociation. Using available collision-theory rate constants for three-body recombination and ionization, together with quantum mechanical estimates of predissociation rates, we predict that the relaxation of the plasma to a high-Rydberg equilibrium outpaces direct three-body dissociative recombination, and, among second-order processes, the rate of two-body electron-cation dissociative recombination substantially exceeds the rate at which the high-Rydberg equilibrium dissociatively relaxes. The rate constant for dissociative recombination extracted from these data conforms with predictions drawn from theory for isolated electron-ion collisions. Methods based on the dissipation of molecular ultracold plasmas may provide a means for estimating rates of dissociative recombination for a variety of complex molecules.
Abstract Double-resonant transitions excite nitric oxide in a seeded supersonic molecular beam, yielding a state-selected Rydberg gas that evolves to form an ultracold plasma. This plasma propagates in z with the molecular beam over a variable distance as great as 600 mm to strike an imaging detector, which records the charge distribution in the dimensions, x and y . The laser-crossed molecular beam excitation geometry convolutes an axial Gaussian distribution of NO about z with the Gaussian intensity distribution of the laser beam about x to create an ellipsoidal volume of Rydberg gas. Plasma images provide evidence for the relaxation of this Rydberg gas volume in an electron impact avalanche that breaks the ellipsoidal symmetry in x to form repelling plasma volumes. We find that the energy deposited in the recoil velocity of mass transport, V x depends systematically on the initially selected Rydberg gas principal quantum number, n 0 , and the initial density of the Rydberg gas, ρ 0 . These quantities combine to determine ρ e , the initial density of electrons formed by the prompt Penning ionization of closely spaced pairs of Rydberg molecules. Above a threshold density of Penning electrons, we find that V x depends linearly on ρ e . We argue that this bifurcation occurs as a consequence of the initial geometry of the Rydberg gas. Ambipolar electron expansion accelerates initially formed core ions. Resonant charge transfer redistributes this ion energy to the column of Rydberg molecules on the long axis of the ellipsoid. The equalized velocities in each direction give rise to a ± x streaming motion that concentrates density in opposing plasma volumes, causing the symmetric gas volume to split like a rotating liquid drop. Significantly, these dynamics reduce electron temperature with little decrease in the ion density or increase in the ion temperature. This appears to facilitate the formation of a strongly coupled plasma.