Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session P09: Photoionization, Photodetachment, and Photodissociation |
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Chair: Robert Lucchese, LBL Room: Wisconsin Center 103DE |
Thursday, May 30, 2019 10:30AM - 10:42AM |
P09.00001: Atomic data for low temperature mid-Z elements for lithography applications Amanda Neukirch, David Kilcrease, Peter Hakel, Christopher Fontes, Manolo Sherrill, James Colgan Strong emission from plasmas of mid-Z elements, such as tin and xenon, in the 11-14 nm wavelength has long been acknowledged as a powerful source of EUV light with significant applications for lithography. We have performed investigations into the complex atomic structure of relevant ion states (from 5 times ionized to 20 times ionized) to model the low temperature (\textless 50 eV) opacity in Xe. It is known that full configuration-interaction (CI) is required to properly describe the strong mixing between the various n$=$4 subshells that give rise to $\Delta $n$=$0 transitions. We find that this technique results in transition energies within 1{\%} of experimental values. Detailed comparisons will be presented. In opacity calculations, large numbers of configurations are necessary to ensure a converged partition function. Full CI calculations for many configurations quickly becomes computationally prohibitive. Instead, we use a model developed for Sn where full CI is utilized for the most important transitions, while intermediate-coupling is used for all other levels. We present opacities generated at temperatures and densities related to lithography applications. Our preliminary results indicate that our models are in good agreement with transmission measurements from laser-produced Sn and Xe plasmas. [Preview Abstract] |
Thursday, May 30, 2019 10:42AM - 10:54AM |
P09.00002: Emission of tin plasmas for lithography applications James Colgan, Amanda Neukirch, David Kilcrease, Joe Abdallah, Manolo Sherrill, Chris Fontes, Peter Hakel, Francesco Torretti, Ruben Schupp, Joris Scheers, Oscar Versolato We employ the Los Alamos suite of atomic physics codes and the plasma kinetics modeling code ATOMIC to compute the LTE emissivity of Sn in plasma regimes of interest to EUV lithography applications. Detailed comparisons are made with laser-produced plasma measurements performed from Sn microdroplets. Excellent agreement is found between the calculations and measurements. The atomic structure calculations had to include significant configuration-interaction effects to properly predict the position of the huge number of transitions that contribute to the Sn emissivity in the EUV wavelength region. We found that excited-to-excited transitions, for which the energy level structure is more difficult to predict, make a surprisingly large contribution to the emissivity in this region. It was also found necessary to vary the scale factors that modify the various integrals within the CATS (Cowan) atomic structure code to obtain best agreement with the measured emission. The computed LTE emission from a single temperature (32 eV) and mass density (0.002 g/cm$^3$) was in very good agreement with the measured emission for both the position and width of the broad, intense emission feature centered at 13.5~nm. [Preview Abstract] |
Thursday, May 30, 2019 10:54AM - 11:06AM |
P09.00003: Characteristic Features of Photoionization of Fe XIX Sultana Nahar Characteristic features of the resonances and background cross sections for photoionization ($\sigma_{PI}$) of oxygen-like iron ion, Fe XIX + h$\nu \rightarrow$ Fe~XX + e, are studied. These features are introduced by excitations of the core ion to states of n=2,3,4 complexes in $\sigma_{PI}$ of the ground, equivalent electron, and single valence electron excited states. Study from a large number of states is important to establish the general properties of photoionization for complex ions. The results correspond to the first detailed study of the ion with a complete set of $\sigma_{PI}$ for 900 bound states with n $\leq$ 10 and $l\leq$ 9 using R-matrix method and close coupling approximation. The ion is of great interest for its lines in the x-ray to UV spectra of astronomical objects and for the solar opacity. It is found that i) the ground and equivalent electron states have high peak narrow Rydberg resonances in the low energy region corresponding to n=2 excitations only, ii) the resonances are stronger for core ion excitations to n=3 complex compared to those for n=2,4, iii) Seaton resonances are also most distinct in the energy region between n=2 to n=3 complexes, and iv) resonances with lower peaks in the energy region between n=3 and n=4 excitation indicate convergence. [Preview Abstract] |
Thursday, May 30, 2019 11:06AM - 11:18AM |
P09.00004: Photoionization of the N$^+$, NH$^+$ and NH$_2^+$ ions in the region of the K-threshold B. M McLaughlin, J.-P. Mosnier, E. T. Kennedy, E. Sokell, J.-M. Bizau, D. Cubaynes, S. Guilbaud, S. Carniato The MAIA photon-ion merged-beam apparatus at the SOLEIL synchrotron in France was used to measure single and double photoionization cross-sections in the photon region straddling the nitrogen K-edge ($\sim$450 eV), for the atomic N$^+$ and molecular NH$^+$ and NH$_2^+$ species. This extends prior work on N$^+$ into the Rydberg region ($1s \rightarrow np$, $n>2$ excitations), manifesting as sharp structures between 420 and 435 eV, up to and over the K-ionization threshold. Photoionization of the NH$^+$ and NH$_2^+$ molecular ions were measured for the first time. The main fragmentation routes following $1s$ excitation in NH$^+$ and NH$_2^+$ produced mostly the N$^{2+}$ species. The spectral patterns are similar to N$^+$: Strong discrete structures near 400 eV ($1s \rightarrow 2p$ excitations), followed by a Rydberg structure in the 410 - 430 eV regions. Significant broadening effects are apparent, testimony to the influence of the molecular vibrational degrees of freedom on the inner-shell photoionization process. The N$^+$ experimental spectra are compared with results of ab-initio RMPS and MCDF calculations, and the molecular spectra with the configuration-interaction single (CIS) method. [Preview Abstract] |
Thursday, May 30, 2019 11:18AM - 11:30AM |
P09.00005: Role of initial-state correlation in one-photon double ionization of atoms and molecules Roger Bello, Frank Yip, Thomas Rescigno, Robert Lucchese, C. William McCurdy By decomposing the initial state wave function into its unique natural orbital expansion, as defined in the 1950s by L\"owdin and used in modern studies of entanglement, we analyze the role of electron correlation in the initial state of an atom or molecule in determining the angular distribution of one-photon double ionization. Final state correlation of the two ejected electrons is treated completely in numerically accurate calculations and the initial states of He, H$^-$ and H$_2$ are built up from correlating configurations in strict order of decreasing natural orbital occupations. In the two-electron atoms it is found that the initial state correlation plays a sometimes modest but generally measurable role. In striking contrast, for H$_2$ a large number of correlating configurations in the ground state is often necessary to produce angular distributions even approximately resembling the correct ones. One-photon double photoionization of oriented H$_2$ is found to be particularly sensitive to left-right correlation along the bond. [Preview Abstract] |
Thursday, May 30, 2019 11:30AM - 11:42AM |
P09.00006: Sequential dissociation of H$_2$O$^{++}$ following double photoionization Z. L. Streeter, C. W. McCurdy, R. L. Lucchese, T. Severt, I. Ben-Itzhak A recent analysis of momentum imaging experiments on the dissociation of the H$_2$O$^{++}$ ion following one-photon double ionization [Phys. Rev. A 98, 053429 (2018)] elucidated the dynamics of direct three-body dissociation to H$^+$ + H$^+$ + O, but also suggested that in one ionization channel a sequential mechanism is involved. Analysis of the momentum imaging data in the native frames of reference associated with each break step confirms sequential dissociation dynamics. A previous study of three-body breakup of H$_2$O$^{++}$ showed sequential dissociation of the $2 ^1A_1$ state by H$_2$O$^{++}$($2 ^1A_1$) $\rightarrow$ OH$^+$($^1\Sigma^+$) $+$ H$^+$ followed by spin-orbit coupling of the $^1\Sigma^+$ and the $^3\Pi$ hydroxyl cation states leading to OH$^+$($^3\Pi$) $\rightarrow$ O($^3$P)$ + $H$^+$. Here we present a theoretical determination of the rovibrational populations of the OH$^+$($^1\Sigma^+$) state from classical trajectories on the H$_2$O$^{++}$($2 ^1A_1$) surface. For two-body dissociation, the resulting internal energy distribution of the OH$^+$($^1\Sigma^+$) cation is binned quasiclassically. The resulting vibrational distribution and coupling to the dissociative OH$^+$($^3\Pi$) state allow comparison with the experimental native frames analysis. [Preview Abstract] |
Thursday, May 30, 2019 11:42AM - 11:54AM |
P09.00007: Photoionization calculations in molecules using an overset grid implementation Carlos Marante, Loren Greenman, Robert L. Lucchese, C. William McCurdy, Thomas N. Rescigno The ultrafast electronic processes in molecules demand, theoretically, the challenging representation of the correlated short-range structure and the asymptotic highly oscillatory behavior of an electron in the continuum at the same time. We solve these requirements using an overset grid implementation, that consist of a central grid and multipole atom-center subgrids, allowing a simultaneous spherical expansions of the wave function about the multiple centers, which together with the Complex Kohn variational method, has proven to be effective in electron-neutral scattering problems, in which applying repeatedly the free particle Green function and potential $\hat{G}_0^+\hat{V}$ onto the channel Bessel function, leads to a Pad\'{e} approximant to the T-matrix. We have extended this formalism to photoionization problems by imposing a fixed spherical boundary matches to Coulomb boundary conditions in the outer region as well as adding a pseudo-potential to enforce orthogonality to the occupied orbitals of the target. We show the performance of the method by computing the valence photoionization cross sections of N$_2$, CF$_4$, SF$_6$ and their electron angular distributions. [Preview Abstract] |
Thursday, May 30, 2019 11:54AM - 12:06PM |
P09.00008: Theoretical and Experimental Search for Evidence of Core Hole Localization in X-ray Photoionization of CCl}$_{\mathrm{\mathbf{4}}}$\textbf{ at the Cl 2p-edge C. S. Trevisan, T. N. Rescigno, C. W. McCurdy, B. Gaire, I. Ben-Itzhak, R. Doerner, Th. Weber Recently, unambiguous evidence of core hole localization in X-ray photoionization of CF$_{\mathrm{4}}$ at the F K-edge was found in the combination of theoretical and experimental determinations of the recoil frame photoelectron angular distributions (RFPADs). In that case, detection of the CF$_{\mathrm{3}}^{\mathrm{+}} \quad +$ F$^{\mathrm{+}}$ fragments following Auger decay in coincidence with the photoelectron verified that the observed RFPAD arose from ionization of the fluorine atom that was ultimately detected as F$^{\mathrm{+}}$ [Phys. Rev. A 95, 011401(R) (2017)]. Similar theoretical calculations of RFPADs for ionization of CCl$_{\mathrm{4}}$ at the Cl 2p L-edge using the Complex Kohn variational method are compared here with COLTRIMS measurements of RFPADs for this case. The localization effect that is evidently related to the strong electronegativity of the F atom was predicted to occur in the case of chlorine which is slightly less electronegative. We explore the comparison of calculated RFPADs from close-coupling calculations for various polarization directions with observations in the CCl$_{\mathrm{3}}^{\mathrm{+}} \quad +$ Cl$^{\mathrm{+}}$ decay channel to search for evidence of the same effect in this system. [Preview Abstract] |
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