Angular momentum dependence of photoionization cross sections from the excited states of lithium

Shahid Hussain, M. Saleem, and M. A. Baig

Phys. Rev. A 74, 052705 – Published 6 November 2006

Abstract

We present new measurements of photoionization cross sections from the $4 s {}^{2}S$ , $4 p {}^{2}P$ , and $4 d {}^{2}D$ excited states of lithium, above the first ionization threshold. The experiments have been conducted using two dye lasers pumped by a Nd:yttrium aluminum garnet (YAG) laser in conjunction with a thermionic diode ion detector and pump-probe saturation technique. The behavior of the photoionization cross sections from $n = 4$ and $l = 0, 1, 2$ excited states have been investigated. A smooth wavelength dependence of photoionization cross sections has been observed for the $4 p$ and $4 d$ excited states, which decrease monotonically with the decrease in the ionizing laser wavelength; however, the falloff for the $4 d$ excited state is purely hydrogenic. The cross section for the $4 s$ excited state first increases, attains a maximum value, and then decreases monotonically with a decrease in the ionizing wavelength—strictly nonhydrogenic. The measured values of the cross section are compared with the earlier theoretical work.

Received 15 August 2006

DOI:https://doi.org/10.1103/PhysRevA.74.052705

Authors & Affiliations

Shahid Hussain, M. Saleem, and M. A. Baig^*

Atomic and Molecular Physics Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan

^*Corresponding author. FAX: +92 51 9210256. Email address: baig@qau.edu.pk

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Issue

Vol. 74, Iss. 5 — November 2006

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Images

Figure 1
(Color online) Schematic diagram of the experimental setup for two-step photoionization of lithium.Reuse & Permissions
Figure 2
Energy level diagram for the measurement of photoionization cross section from the $4 s$ , $4 p$ , and $4 d$ excited states of lithium. The level energies are taken from NIST data [16].Reuse & Permissions
Figure 3
(Color online) The photoionization data for the $4 s {}^{2}S$ , $4 p {}^{2}P$ , and $4 d {}^{2}D$ excited states of lithium with the ionizing laser set to a wavelength of $1064 nm$ . The solid lines are the least squares fit to Eq. (2) to the observed data for extracting the photoionization cross section. The error limits on the data results from pulse-to-pulse fluctuations in the signal.Reuse & Permissions
Figure 4
(Color online) (a) Comparison of the experimentally measured values of the absolute photoionization cross section from the $4 s {}^{2}S$ excited state with the theoretical work. The solid line is the calculated curve presented by Lahiri and Manson [10]. The calculated values at threshold by Aymar et al. [5] and by Gezalov and Ivanova [7] are also shown. (b) Comparison of the experimentally measured values of the absolute photoionization cross section from the $4 p {}^{2}P$ excited state with the theoretical work. The solid line is the calculated curve presented by Lahiri and Manson [10]. The calculated values at threshold by Aymar et al. [5] and by Gezalov and Ivanova [7] are also shown. The dotted line is the exponential decay fit to the experimental data points. (c) The experimentally measured values of the absolute photoionization cross section from the $4 d {}^{2}D$ excited state are shown along with the calculated values at threshold by Aymar et al. [5] and by Gezalov and Ivanova [7]. The solid line is the exponential decay fit to the experimental data points. The dotted part of the line is the extrapolation.Reuse & Permissions
Figure 5
(Color online) A comparison between the energy-dependent behavior of the measured values of the photoionization cross section from the $4 s$ , $4 p$ , and $4 d$ excited states of lithium. The values of the photoionization cross section from the $4 s$ excited state are multiplied by 30 just to show the trends of cross section from the three excited states. The dotted line passing through the values of the cross section of the $4 s$ excited state is not the fitted curve, it is just a freehand sketch. The solid lines are the exponential decay fit to the experimental data points for the photoionization cross section from the $4 p$ and $4 d$ excited states.Reuse & Permissions

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