Using a crossed atomic and laser beams set-up with mass spectrometric ion detection we have studied the photoionization of laser-excited, aligned Ar * (3p 5 4p 3 D 3 ) atoms from the Ar + ( 2 P 3/2 ) threshold up to photoelectron energies of ε = 0.846 eV. Absolute cross sections are reported for parallel (η = 0 • ) and perpendicular (η = 90 • ) polarization directions of the linearly polarized exciting and ionizing CW lasers over the range ε = 0-0.2 eV. The cross sections exhibit nd (J = 2, 3) autoionization resonances whose combined appearance varies with angle η; this behaviour is traced to the η dependence of the partial cross sections for the final (ion + electron) channels with different total angular momentum, J 1 . Using theoretical formulae whose derivation is outlined we determine the energy dependence of these partial cross sections from least squares fits to the data measured at η = 0 • and 90 • . Experimental results are also presented for the asymmetry function, A LD (η), which describes the linear dichroism for the photoionization of aligned Ar * (4p 3 D 3 ) atoms, and for the full η dependence of the ionization cross section as obtained for 10 selected photoelectron energies in the range (0.017-0.846) eV. Many-electron calculations have been carried out which provide additional insight into the photoionization dynamics. In contrast to the situation for Ne * (3p, J = 3), photoionization of Ar * (4p, J = 3) is not well described by just two reduced matrix elements D s , D d . 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 associated with the Ar + ( 2 P 3/2 ) formation. Satisfactory overall agreement is observed between the experimental and theoretical cross sections and their polarization dependence. The calculations also provide information on the weak g-wave contributions and on the cross section for leaving the ion in the excited Ar + ( 2 P 1/2 ) level; the latter amounts to about 1% relative to Ar + ( 2 P 3/2 ) formation in agreement with experimental and MQDT estimates.

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Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract. A novel, accurate method tbr the absolute detection of metastable rare gas atoms is described and demonstrated. It involves a direct in situ determination of the electron emission coefficient ? for impact of the respective metastable atom on a conducting surface, y is reliably obtained by a cw two-photon ionization -depletion technique: the reduction A I s in electron current from the detector surface due to efficient photoionization removal of the metastable flux is compared with the photoelectron current A I p ( y = A I s / A I e ) . The principle of the method, possible realization schemes for the different metastable rare gas atoms and the apparatus are described in detail. The method has been applied so far to metastable Ne* (3s 3P2), Ar* (4s 3P2), and Kr* (5s 3P2) atoms, and corresponding results for y, obtained with five different chemically clean, polycrystalline surface materials and at two surface temperatures (300 K, 360 K) are reported. Whereas for Ne*, the value of y (~0.35) showed only a rather weak dependence on the surface material and temperature (as also found for a mixed He* (23S, 21S) beam), strong variations in ?, especially at 300 K, were detected for Ar* and Kr* (values between 0.25 and 0.003). Some applications of the described method, especially with regard to the determination of absolute reaction cross sections involving metastable rare gas atoms, are discussed.

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.

The state dependence of the interaction of metastable rare gas atoms Rg* (ms 3P2, 3P0) (Rg = Ne, Ar, Kr, Xe) with ground state sodium atoms Schohl, S.; Müller, M.W.; Meijer, H.A.J.; Ruf, M.-W.; Hotop, H.; Morgner, H. Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Schohl, S., Müller, M. W., Meijer, H. A. J., Ruf, M-W., Hotop, H., & Morgner, H. (1990). The state dependence of the interaction of metastable rare gas atoms Rg* (ms 3P2, 3P0) (Rg = Ne, Ar, Kr, Xe) with ground state sodium atoms. Default journal. CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Using crossed beams of metastable rare gas atoms Rg*(ms 3P2, 3Po) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s 2S1/2), we have measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies. For Rg*(3P2)+Na(3s), the spectra are quite similar for the different rare gases, both in width and shape; they reflect attractive interactions in the entrance channel with well depths D* [meV] decreasing slowly from R g = N e to Xe as follows: 676(18); 602(23); 565(26); 555(30). For Rg*(3~)+Na(3s), the spectra vary strongly with the rare gas, indicating a change in the character of the interaction from van der Waals type attraction (Ne) to chemical binding for Kr and Xe with well depths D* [meV] of: 51(I9); 107(25); 432(30); 530(50). These findings are explained through model calculations of the respective potential curves, in which the exchange and the spin orbit interaction in the excited rare gas and the molecular interaction between the two valence s-electrons in terms of suitably chosen singlet and triplet potentials are taken into account. These calculations also explain qualitatively the experimental finding that the ratios q2/qo of the ionization cross sections for Rg* (3P2)+Na and Rg* (3Po)+ Na vary strongly with the rare gas fromNe to Xe as follows: 15.8(3.2); 2.6(4); 1.4(2); 1.6(4).