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

Abstract

The existence of a Cooper minimum in the experimentally measured photoionization cross sections for the 7s 2 S 1/2 excited state of potassium has been reported using a two-step laser excitation technique in conjunction with a time-of-flight mass spectrometer. The photoionization cross sections for the 7s 2 S 1/2 state have been determined as (9.78 ± 0.01) × 10 −2 , (3.30 ± 0.49) × 10 −4 , (5.47 ± 0.82) × 10 −3 , and (2.06 ± 0.30) × 10 −2 Mb at the ionizing laser wavelengths 1064, 700, 532, and 355 nm, respectively, that validate the presence of a Cooper minimum at ∼ =1.25 eV above the first ionization threshold. The number density has been determined as N 0 = 2 × 10 11 cm −3 .The experimentally determined absolute values of the cross sections are in qualitative agreement with the theoretical predictions.

Photoionization of the francium 7P3/2 state

“…Additionally, photoionization cross-section measurements have been performed for many other excited states of the aklalis, e.g. [23][24][25] for Li, [23,26] for Na, and [27][28][29][30] for K. For our 442 nm light photoionizing the 7P 3/2 state, the photoelectron energy is E e = 0.46 eV. We can obtain experimental cross-sections near our photoelectron energy for the other alkalis and compare with our result for francium.…”

A Fully Relativistic Approach to Photon Scattering and Photoionization of Alkali Atoms

“…They found quadrupole core polarization to be important and obtained excellent agreement with experiment for the 4s photoionization cross section, including in the region of the Cooper minimum. The results of Zatsarinny and Tayal [30] are in excellent agreement with more recent experiments [16,[20][21][22] but are generally in poor agreement with previous calculations. The purpose of this paper is to investigate the origin of the differences between the results of Zatsarinny and Tayal and previous theoretical calculations.…”

“…After fitting to resonant transition oscillator strengths, we found that calculations performed using the three different forms of the modified dipole operator-two analytic, ( 21) and (22), and one numerical-produce cross sections that are practically indistinguishable. In what follows, we will use only the modified dipole operator given by (21) with parameters given in Table 1.…”

“…Sandner et al [16] experimentally measured the ground state photoionization cross section of potassium using a time-of-flight technique that entirely avoids the problem of molecular photoionization that was present in earlier experiments. Since the experiment of Sandner et al [16], there have been various experiments that have measured photoionization cross sections for the ground and excited states of the alkali atoms [17][18][19][20][21][22]. The agreement between different experiments has improved in recent times.…”

Photoionization cross section measurements of the excited states of cobalt in the near-threshold region

“…[1][2][3][4][5][6][7][8][9][10][11] In most of the experimental studies, the two-color, two-step resonance ionization technique was used to measure the photoionization cross-sections of the valence-electron excited states and the excited-state lifetimes. [4][5][6][9][10][11][12] In contrast to the photoionization studies of alkali atoms and alkaline-earth-metal atoms, few experimental or theoretical studies have focused on the valence-electron excited states of transitionmetal atoms. In terms of experimental considerations, such studies have been hindered by the high melting points and low vapor pressures of transition metals.…”