Phys. Rev. Lett. 88, 203002 (2002) [4 pages]Photoexcitation of a Dipole-Forbidden Resonance in HeliumReceived 13 December 2001; published 2 May 2002 We have observed photoexcitation of the dipole-forbidden 1s21S0→2p21D2 resonance in helium by measuring the nondipolar forward-backward asymmetry of photoelectron angular distributions in the 2ℓ2ℓ′ autoionizing region. By exploiting the electric dipole-quadrupole interference in the excitation of both the 2s2p1P1 and 2p21D2 levels, we have observed the quadrupole resonance in photoabsorption and extracted its Fano line shape parameters and the relative phase of the 1sEp and 1sEd continua. We find the quadrupole line profile index q2 to be markedly different from theoretical expectations. © 2002 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.88.203002
DOI:
10.1103/PhysRevLett.88.203002
PACS:
32.80.Dz, 32.80.Fb
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