Angular distributions of photoelectrons from polarized atoms near threshold: experimental results and theoretical analysis

Abstract

Following our recent mass spectrometric study of wavelength-dependent photoionization of laser-excited, polarized Ar * (4p, J = 3) atoms near threshold (1997 J. Phys. B: At. Mol. Opt. Phys. 30 609) we report electron angular distributions for photoionization of polarized Ar * (4p, J = 3) atoms at four energies (ε = 23, 144, 316, 846 meV) above the Ar + ( 2 P 3/2 ) threshold. The measurements allow us to both check the atomic alignment produced in the optical pumping process and test in detail results of theoretical many-electron calculations for the relevant reduced dipole matrix elements and phase shifts. In contrast to the situation for Ne * (3p, J = 3) (1983 J. Phys. B: At. Mol. Phys. 16 2945), photoionization of Ar * (4p, J = 3) cannot be simply described by two reduced matrix elements D s and D d and a single phase difference = δ d − δ s . For Ar * the term dependence of the Hartree-Fock wavefunctions and correlation effects lead to substantial differences between the reduced matrix elements for the five d-wave channels and between the five existing phase differences. The comparison of the experimental angular distributions with those calculated theoretically shows that good agreement is obtained when the theoretical values of the reduced matrix elements for the d-wave channels are increased (relative to that for the s-wave channel) by a common, energy-dependent factor; this finding is in accord with conclusions from the polarization-dependent ion production data. The correction factors range from 1.4 to 1.1 (ε = 23-846 meV) for calculations which include long-range core polarization effects, while they amount to values between 2.0 and 1.5 when core polarization effects are neglected.

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

“…We note a printing error in (A10a) where the third term should read +(1/ √ 2)ν cos ∆. We also mention that the sign of the ratio ν in [28] (due to the use of the pseudostandard phase convention in [28] for which the ratio d||C 1 ||p s||C 1 ||p is negative) is defined to be opposite to the sign of our ratios ν (which are negative near threshold). This aspect is taken into account in the comparison of our theoretical ratios cos(δ d −δ s ) with the values derived from the experiments (which yield the sign of the product ν cos(δ d − δ s )).…”

“…The polarization dependent ion data and the electron angular distributions were analyzed on the basis of formulae, given explicitly in [27,28] for photoionization of atoms with total angular momentum J = 3, resulting from the coupling of two subsystems i (i = 1, 2) which both possess angular momenta j i = 3/2. In the present case i = 1 corresponds to the excited 4p (j 1 = 3/2) electron and i = 2 to the nuclear spin of 39 K (j 2 = 3/2).…”

“…We assume the nuclear spin to be frozen in the photoionization process (see the corresponding discussion in the literature [29]); moreover, we neglect -as corroborated by the theoretical results -the effects of spin-orbit coupling which could result in a difference between the phase shifts for the d 3/2 and the d 5/2 waves. Thus we obtain simplified formulae [25,27,28] which only contain the relevant two reduced matrix elements D s and D d , the phase shift difference δ d − δ s and -as an experimental parameter -the effective quadrupole alignment of the 4p 3/2 electron. The alignment was determined from the angular distribution of the resonance fluorescence using formulae given in [29].…”

“…For the analysis of the ion data we used equations (18,19) from [27]. The electron angular distributions were analysed on the basis of formulae (6a, 6b) in [28] in conjunction with equations (A10a-A10e) in [28]. We note a printing error in (A10a) where the third term should read +(1/ √ 2)ν cos ∆.…”

Photoelectron angular distributions from autoionizing 4s14p66p1 states in atomic krypton probed with femtosecond time resolution

“…[1][2][3][4][5][6][7][8][9][10] As a probe of chemical dynamics, PADs are promising as a sensitive tool to track changes in electronic surfaces as a chemical reaction is evolving. The nature of the excited state is uniquely imprinted on the continuum electron partial waves as interference patterns measured in the PAD.…”