Near threshold photoionization of excited alkali atoms Ak(np) (Ak = Na, K, Rb, Cs; n = 3-6)

Abstract

The effect of the polarization of the atomic core by the outer electron on near threshold photoionization of excited alkali atoms Ak(np) (Ak = Na-Cs; n = 3−6) is investigated. Partial and total cross-sections for photo-ionization of the np-electron were computed utilizing the configuration interaction technique with Pauli-Fock atomic orbitals (CIPF) and including the long range core polarization potential (CP). To calculate the core polarization potential the variational principle is applied. Comparison with previous theoretical results and with available experimental data is made for the total cross-section σ, for the electron angular distribution parameter β, for the ratio ν = |D d /Ds| of the reduced electric dipole matrix elements and for the phase shift difference ∆ = δ d − δs, associated with the d-wave and s-wave continua, respectively. In the comparison, new experimental results for σ, ν, and ∆, measured for laser-excited, polarized 39 K(4p 3/2 ) atoms, have been included.PACS. 32.80.Fb Photoionization of atoms and ions -33.60.-q Photoelectron spectra -31.50.+w Excited states

Evidence of a Cooper minimum in the photoionization from the7s2S1/2excited state of potassium

“…The photoionization cross section from the 4p level has a lower value at the ionization threshold, achieves a higher value at about 0.5 eV above the threshold, and then decreases monotonically [13]. The photoionization cross section from the 6p level shows an increasing trend from the ionization threshold whereas a Cooper minimum in the photoionization from the 4s level has been studied by Sandner et al [10].…”

“…The existence of the Cooper minimum in photoionization cross sections has been investigated experimentally and theoretically [1][2][3][4][5][6][7][8][9][10][11] in transitions from the ground state of alkali metals and in particular for potassium atoms. However, the Cooper minimum in the transitions from the excited states of alkali metals has been reported [12][13][14] recently; these reports presented experimental evidence for verification of this phenomenon.…”

“…Petrov et al [13] reported the effect of the polarization of the atomic core by the outer electron on the near-threshold photoionization of the excited alkali-metal atom. Beterov et al [14] reported the anomalous behavior for the S series, the rate of high-lying Rydberg levels as a function of n using blackbody radiations which was found to be similar to the occurrence of the Cooper minimum in the discrete spectrum.…”

Resonance and Threshold Phenomena in Low-Energy Electron Collisions with Molecules and Clusters

“…39 K(4s 1/2 , F ¼ 1, 2) atoms to the intermediate levels 40 Ar * (4p 3 D 3 ) or 39 K * (4p 3/2 , F 0 ¼ 2, 3) (quasi-stationary excited state population nearly 50%), is optimized in the sense that the cross-section for ionization of Ar * (4p 3 D 3 ) (Schohl et al, 1997) as well as for K * (4p 3/2 ) atoms (Petrov et al, 2000) is substantial (around 10 À21 m 2 ) and three to four orders of magnitude higher than that for ionization of metastable Ar * (4s 3 P 2 ) atoms (Kau et al, 1998;Petrov et al, 1999) or ground state K(4s) atoms (Sandner et al, 1981), respectively. We note that an analogous two-step photoionization scheme involving ground state Na(3s 1/2 ) atoms has been recently applied by Keil et al (1999) to study laser photoelectron attachment to vibrationally excited Na 2 molecules (see Section IV.B).…”

Detailed observation of space–charge dynamics using ultracold ion bunches

“…1c). Field ionization was represented by rate G 34 , which was determined from calculated near-threshold ionization cross-sections 40 . The evolution of r, the density matrix for the four-level atom, is given by…”