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

Journal of Physics B Atomic Molecular and Optical Physics

The state multipoles of the n=2 state of atomic hydrogen

Jim Williams, E L Heck

Published May 14, 1988• 12 citations
Publisher

Abstract

A determination of all the state multipoles of the n=2 excited state of atomic hydrogen has been made. The kinematical conditions were a crossed electron-atom-beam geometry in which the incident electron energy was 350 eV and the scattering angle 3'. The experimental technique measures the scattered 10.2 eV energy loss electrons in coincidence with the 10.2 eV photons from either the 2P state or the delayed Stark-quenched 2S-state decay. An external electrostatic field mixes the S and P states, permitting the observation of their coherence by measuring the linear and circular photon polarisations, while in-plane angular correlations for a zero electric field determine the P-state multipoles. The state multipoles were deduced from a least-squares fit of the measured data to the quantum mechanical expressions determined for a model of an S-P (m j =1/2) superposition excited state with averages over the singlet and triplet spin states.

DOI
10.1088/0953-4075/21/9/020

Related papers

Electron impact excitation of 2p states in atomic hydrogen

Marcin L. Gradziel

This thesis presents the results of experimental investigation of coherence in the excitation of the 2p states of atomic hydrogen through a collision with an unpolarised electron. The polarisation correlation variation of the delayed coincidence method has been employed to simultaneously measure the reduced Stokes parameters P1,P2 and P3, which are needed to fully characterise the state of the atom immediately after the collision. This has also allowed the excitation coherence parameter P+ to be determined directly. In the case of the excitation of 2p states of hydrogen, a deviation of P+ from unity is indicative of the importance of spin exchange during the collision. A new Lyman- polarisation analyser, that permits independent rotation of a retarder and a linear polariser, was developed for this work. A novel approach to the analysis of data from electron-photon coincidence measurements has been implemented to improve the quality of the final results. The reduced Stokes parameters P1,P2 and P3 were measured at 54.4 eV electron energy, and in the 4-40 range of electron scattering angles. The P1 and P2 results are consistent with the earlier measurements, and recent theoretical predictions. The new P3 results, however, deviate significantly from the predictions of all modern theories, and also differ from previous experimental results. The newly measured values of P+ also suggest less coherent excitation than predicted by the theory, even at a relatively low scattering angle of 30. Several possible sources of systematic error including resonance radiation trapping, Stark mixing and erroneous phase-shift of the retarder have been considered, but are insufficient to explain the observed deviations from theory. Therefore, we are forced to conclude that spin exchange may play a more significant role during the collision than current theoretical methods predict.

•Jul 1, 2003•0 citations

Electron-photon angular correlation measurements for the 2P state of hydrogen at 35 eV

J. A. Slevin, M. Eminyan, J. M. Woolsey +4 more

Electron-photon angular correlations have been measured for excitation of the $2P$ states of hydrogen at an incident energy of 35 eV. The data presented relate to electron-scattering angles from ${\ensuremath{\theta}}_{e}=8\ifmmode^\circ\else\textdegree\fi{}$ to ${\ensuremath{\theta}}_{e}=120\ifmmode^\circ\else\textdegree\fi{}$ and yield values for the parameters $\ensuremath{\lambda}$ and $R$. The experimental results are compared with several theories. In general, none of the theories is found to be adequate at this energy.

Physical Review A•Sep 1, 1982•31 citations

Angular correlations between sequential cascading photons fromn=3 atomic hydrogen

Jim Williams, Mukesh Kumar, A. T. Stelbovics

We report the first measurements and associated theory for angular correlations of sequential cascading photons for an atomic system in which a scattering plane is defined. The cascade radiation from the n=3 levels of atomic hydrogen excited by 290 eV electrons is observed. The first determinations of a rank-4 multipole and of the magnetic sublevels of the 3d state have been made. The measured angular correlations and the deduced multipole moments have order-of-magnitude agreement with Glauber, Born, and six-state close-coupling model predictions.

Physical Review Letters•Mar 1, 1993•10 citations

Stark-induced anapole magnetic fields inn= 2 hydrogen

Robert R. Lewis, A. Góngora-T

This paper presents results for the anapole magnetic field moment due to the mixing of states with opposite parity in the n = 2 hydrogen atom in an external constant electric field. The evaluation of the current densities of the four n = 2 states is carried out to first order in the field strength. These current densities and their associated magnetic fields are expanded in multipoles, including both the ordinary poloidal and the toroidal fields. The dominant contribution to the toroidal dipole (anapole) magnetic field comes from the strong mixing of the degenerate 2S, 2P states within the n = 2 shell. A brief discussion is also presented of the electronic scattering from the anapole field of a Rydberg atom. The experimental conditions under which the atomic anapole field could be detected are critically considered, in particular, in terms of the quasi-resonant dependence of the anapole field on the applied electric field.

Journal of Physics B Atomic Molecular and Optical Physics•Aug 28, 1998•3 citations

Time-dependent Stark-perturbed Stokes parameters in atomic hydrogen

E L Heck, Jim Williams

The 2S and 2P states of atomic hydrogen are excited by 350 eV electrons in the presence of a parallel electric field of 250 V cm -1 . The time decay of the Stark-perturbed states has been observed through the detection of the 10.2 eV energy loss scattered electrons in coincidence with the 121.6 nm circularly polarised photons. The time development of the eta 2 Stokes parameter shows well defined Lamb shift beats with a period of 0.7 ns; the sign of eta 2 changes as the sign of the electric field changes. With a negative electric field eta 2 changes from negative to positive values after 3 ns indicating a relative change in the decay of the 2S and 2P states. This behaviour is explained in terms of the time development coefficients and their dependence on the electric field. These measurements are the most sensitive test of scattering theory and are in good agreement with the prediction of van Wyngaarden and Walters (1985) at 350 eV and 3 degrees scattering angle.

Journal of Physics B Atomic and Molecular Physics•Jun 28, 1987•14 citations

Excitation and decay of Stark-mixed n=2 states of hydrogen observed in an electron-photon coincidence experiment

C G Back, Simon Watkin, M. Eminyan +3 more

Measurements have been made of the Lyman- alpha intensity from Stark-mixed n=2 states of hydrogen, using the electron-photon coincidence technique at an incident electron energy of 350 eV. The data are related to a combination of excitation amplitudes, including a term which depends on the relative phase of S and P amplitudes. Field-free measurements of lambda and R have also been made at this energy. Comparison is made with several theoretical results.

Journal of Physics B Atomic and Molecular Physics•Jul 14, 1984•18 citations
A determination of all the state multipoles of the n=2 excited state of atomic hydrogen has been made. The kinematical conditions were a crossed electron-atom-beam geometry in which the incident electron energy was 350 eV and the scattering angle 3'. The experimental technique measures the scattered 10.2 eV energy loss electrons in coincidence with the 10.2 eV photons from either the 2P state or the delayed Stark-quenched 2S-state decay. An external electrostatic field mixes the S and P states, permitting the observation of their coherence by measuring the linear and circular photon polarisations, while in-plane angular correlations for a zero electric field determine the P-state multipoles. The state multipoles were deduced from a least-squares fit of the measured data to the quantum mechanical expressions determined for a model of an S-P (m j =1/2) superposition excited state with averages over the singlet and triplet spin states.
This thesis presents the results of experimental investigation of coherence in the excitation of the 2p states of atomic hydrogen through a collision with an unpolarised electron. The polarisation correlation variation of the delayed coincidence method has been employed to simultaneously measure the reduced Stokes parameters P1,P2 and P3, which are needed to fully characterise the state of the atom immediately after the collision. This has also allowed the excitation coherence parameter P+ to be determined directly. In the case of the excitation of 2p states of hydrogen, a deviation of P+ from unity is indicative of the importance of spin exchange during the collision. A new Lyman- polarisation analyser, that permits independent rotation of a retarder and a linear polariser, was developed for this work. A novel approach to the analysis of data from electron-photon coincidence measurements has been implemented to improve the quality of the final results. The reduced Stokes parameters P1,P2 and P3 were measured at 54.4 eV electron energy, and in the 4-40 range of electron scattering angles. The P1 and P2 results are consistent with the earlier measurements, and recent theoretical predictions. The new P3 results, however, deviate significantly from the predictions of all modern theories, and also differ from previous experimental results. The newly measured values of P+ also suggest less coherent excitation than predicted by the theory, even at a relatively low scattering angle of 30. Several possible sources of systematic error including resonance radiation trapping, Stark mixing and erroneous phase-shift of the retarder have been considered, but are insufficient to explain the observed deviations from theory. Therefore, we are forced to conclude that spin exchange may play a more significant role during the collision than current theoretical methods predict.
Electron-photon angular correlations have been measured for excitation of the 2P2P2P states of hydrogen at an incident energy of 35 eV. The data presented relate to electron-scattering angles from ${\ensuremath{\theta}}_{e}=8\ifmmode^\circ\else\textdegree\fi{}$ to ${\ensuremath{\theta}}_{e}=120\ifmmode^\circ\else\textdegree\fi{}$ and yield values for the parameters $\ensuremath{\lambda}$ and RRR. The experimental results are compared with several theories. In general, none of the theories is found to be adequate at this energy.
We report the first measurements and associated theory for angular correlations of sequential cascading photons for an atomic system in which a scattering plane is defined. The cascade radiation from the n=3 levels of atomic hydrogen excited by 290 eV electrons is observed. The first determinations of a rank-4 multipole and of the magnetic sublevels of the 3d state have been made. The measured angular correlations and the deduced multipole moments have order-of-magnitude agreement with Glauber, Born, and six-state close-coupling model predictions.
This paper presents results for the anapole magnetic field moment due to the mixing of states with opposite parity in the n = 2 hydrogen atom in an external constant electric field. The evaluation of the current densities of the four n = 2 states is carried out to first order in the field strength. These current densities and their associated magnetic fields are expanded in multipoles, including both the ordinary poloidal and the toroidal fields. The dominant contribution to the toroidal dipole (anapole) magnetic field comes from the strong mixing of the degenerate 2S, 2P states within the n = 2 shell. A brief discussion is also presented of the electronic scattering from the anapole field of a Rydberg atom. The experimental conditions under which the atomic anapole field could be detected are critically considered, in particular, in terms of the quasi-resonant dependence of the anapole field on the applied electric field.
The 2S and 2P states of atomic hydrogen are excited by 350 eV electrons in the presence of a parallel electric field of 250 V cm -1 . The time decay of the Stark-perturbed states has been observed through the detection of the 10.2 eV energy loss scattered electrons in coincidence with the 121.6 nm circularly polarised photons. The time development of the eta 2 Stokes parameter shows well defined Lamb shift beats with a period of 0.7 ns; the sign of eta 2 changes as the sign of the electric field changes. With a negative electric field eta 2 changes from negative to positive values after 3 ns indicating a relative change in the decay of the 2S and 2P states. This behaviour is explained in terms of the time development coefficients and their dependence on the electric field. These measurements are the most sensitive test of scattering theory and are in good agreement with the prediction of van Wyngaarden and Walters (1985) at 350 eV and 3 degrees scattering angle.