Photoexcitation of a Dipole-Forbidden Resonance in Helium

B. Krässig; E. P. Kanter; S. H. Southworth; R. Guillemin; O. Hemmers; D. W. Lindle; R. Wehlitz; N. L. S. Martin

doi:10.1103/PhysRevLett.88.203002

Photoexcitation of a Dipole-Forbidden Resonance in Helium

B. Krässig, E. P. Kanter, S. H. Southworth, R. Guillemin, O. Hemmers, D. W. Lindle, R. Wehlitz, and N. L. S. Martin

Phys. Rev. Lett. 88, 203002 – Published 2 May 2002

Abstract

We have observed photoexcitation of the dipole-forbidden ${1 s}^{2} {}^{1}S_{0} \to {2 p}^{2} {}^{1}D_{2}$ resonance in helium by measuring the nondipolar forward-backward asymmetry of photoelectron angular distributions in the $2 ℓ 2 ℓ^{'}$ autoionizing region. By exploiting the electric dipole-quadrupole interference in the excitation of both the $2 s 2 p {}^{1}P_{1}$ and ${2 p}^{2} {}^{1}D_{2}$ levels, we have observed the quadrupole resonance in photoabsorption and extracted its Fano line shape parameters and the relative phase of the $1 s E p$ and $1 s E d$ continua. We find the quadrupole line profile index $q_{2}$ to be markedly different from theoretical expectations.

Received 13 December 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.203002

Authors & Affiliations

B. Krässig¹, E. P. Kanter¹, S. H. Southworth¹, R. Guillemin², O. Hemmers², D. W. Lindle², R. Wehlitz³, and N. L. S. Martin⁴

¹Argonne National Laboratory, Argonne, Illinois 60439
²Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154
³Synchrotron Radiation Center, University of Wisconsin, Stoughton, Wisconsin 53589
⁴Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506