Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session N4: Ion-atom Collisions |
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Chair: Charles Havener, Oak Ridge National Laboratory Room: 204 |
Thursday, June 6, 2013 10:30AM - 10:42AM |
N4.00001: Comparative study of the \textit{ab initio} potential curves for Be$_2^+$, Mg$_2^+$, Ca$_2^+$ and Sr$_2^+$ molecular ions Sandipan Banerjee, John Montgomery, Robin C\^ot\'e We perform a comparative study of the X~$^2 \Sigma_{u}^+$, A~$^2\Pi_u$ and B~$^2 \Sigma_{g}^+$ states in the homonuclear alkaline-earth family of molecular ions --- Be$_2^+$, Mg$_2^+$, Ca$_2^+$ and Sr$_2^+$. A qualitative comparison of the ``double-well" in the B~$^2 \Sigma_{g}^+$ state and interaction with the excited 2~$^2 \Sigma_{g}^+$ state is made for all the molecular ions. Multireference configuration interaction (MRCI) calculations are performed with a complete active space (CAS) wavefunction as reference. Spectroscopic constants, bound vibrational levels, transition moments and radiative lifetimes are calculated. The static dipole and quadrupole polarizabilities, and the leading order van der Waals coefficients are also reported. We also show preliminary results for corrections to the Born-Oppenheimer Hamiltonian --- non-adiabatic couplings and and hyperfine structure due to nuclear spins and electric quadrupoles. [Preview Abstract] |
Thursday, June 6, 2013 10:42AM - 10:54AM |
N4.00002: Charge transfer in ultracold atom-ion alkaline-earth systems Diego Valente, Sandipan Banerjee, Robin C\^ot\'e We explore the collision properties of alkaline-earth systems comprised of ions and their neutral parent atoms in the low and ultralow energy regimes. The long-range attractive potential ($\sim1/R^{4}$) characteristic of atom-ion systems gives rise to collisions involving higher order partial waves that present an important contribution to the cross sections even in the ultracold regime. We calculate the elastic and charge-transfer cross sections using accurate potential curves, and investigate how the quantal treatment of the charge-transfer cross section compares to that of a semiclassical Langevin model. We present calculations for several alkaline-earth systems, including Be-Be$^{+}$, Mg-Mg$^{+}$, Ca-Ca$^{+}$, Sr-Sr$^{+}$, and show how charge transfer processes are highly efficient in these systems. [Preview Abstract] |
Thursday, June 6, 2013 10:54AM - 11:06AM |
N4.00003: Strong multiple-capture effect in slow Ar$^{17+}$-Ar collisions: a quantum mechanical analysis Arash Salehzadeh, Tom Kirchner A recent X-ray spectroscopy experiment on 255 keV Ar$^{17+}$-Ar collisions provided evidence for strong multiple-electron capture [1]. We have coupled a quantum-mechanical independent-electron model calculation for the collision dynamics with (semi-) phenomenological Auger and radiative cascade models to test this finding. The capture calculations are performed using the basis generator method and include single-particle states on the projectile up to the 10$^{\rm th}$ shell. The cross sections obtained for shell-specific multiple capture are fed into an Auger decay scheme in order to obtain $n$-specific cross sections for {\it apparent} single (and double) capture that together with the {\it actual} single capture cross sections are then fed into a radiative cascade code. This yields X-ray emission intensities that can be compared with the experimental data of [1]. Good agreement is found for the Lyman series from $n=3$ to $n=7$ if the multiple-capture contributions are included, whereas calculations that ignore them are in stark conflict with the measurements [2].\\[4pt] [1] M. Trassinelli {\it et al.}, J. Phys. B \textbf{45}, 085202 (2012);\\[0pt] [2] A. Salehzadeh and T. Kirchner, J. Phys. B \textbf{46}, 025201 (2013). [Preview Abstract] |
Thursday, June 6, 2013 11:06AM - 11:18AM |
N4.00004: Theoretical investigation of collisions between highly-charged N$^{5+}$ and N$^{6+}$ with He Y. Wu, L. Liu, L.L. Yan, C.L. Zhang, J.G. Wang, P.C. Stancil, H.P. Liebermann, R.J. Buenker For X-rays and/or EUV photons observed in cometary and planetary atmospheres and from the heliosphere, a primary production mechanism is charge exchange (CX) due to the collision between highly charged solar wind ions and ambient neutral species. In the present work, CX due to N$^{6+}$($1s~^2S$)-He and N$^{5+}$($1s^2~^1S$)-He collisions has been investigated using the quantum-mechanical molecular-orbital close-coupling (QMOCC) and the atomic-orbital close-coupling (AOCC) methods. For the high charged N$^{5+}$ and N$^{6+}$, the electrons of He will be captured to very highly excited or doubly-excited states, which may lie in continua of various quasi-molecular channels. The multi-reference single- and double-excitation configuration interaction approach (MRDCI) has been applied and a large number of important configurations have been selected to compute the adiabatic potential and nonadiabatic couplings. Total and state-selective cross sections are calculated for energies between 10 meV/u and 10 keV/u and the autoionization process has been treated quasi-classically. The QMOCC results are compared to available experimental and theoretical data as well AOCC calculations. [Preview Abstract] |
Thursday, June 6, 2013 11:18AM - 11:30AM |
N4.00005: Calculating Auger Lifetimes Directly from Time Propagation using the Multiconfiguration Time-Dependent Hartree-Fock Method Brant Abeln, C. William McCurdy, Daniel Haxton A recent implementation of the multiconfiguration time-dependent Hartree-Fock (MCTDHF) method using an underlying discrete variable representation for the time dependent orbitals as well exterior complex scaling of all electronic coordinates is used to calculate Auger decay rates for states of Be$^+$. In this approach all electrons are active and the number of orbitals and thus the size of the configuration space can be increased to give improved descriptions of these metastable states. After first populating the $1s2s^2$ $(^2S)$, and the two $1s2s2p$ $(^2P)$ metastable states, we calculated the autocorrelation function of the initial wave function under field-free propagation. In the simplest approach, the Fourier Transform of the autocorrelation function, $\langle \Psi(0)|\Psi(t) \rangle$, can be fit to a Breit-Wigner profile to extract the lifetime and energy of the Auger decaying states. We discuss this and other methods of using MCTDHF to compute the lifetimes of core excited states of atoms and diatomic molecules using this three-electron system as the test case. [Preview Abstract] |
Thursday, June 6, 2013 11:30AM - 11:42AM |
N4.00006: Towards imaging the folding of single biomolecules in an ion trap Erik Streed Recent advances in imaging of single trapped atomic ions have demonstrated wavelength-scale fluorescence and absorption imaging (Streed et al. Nat. Comm 3 933 (2012)). We propose adapting these imaging techniques to investigate the folding properties of biological molecules in the gas phase. Trapped-ion mass spectrometry is a well-established technique for compositional analysis of biomolecules from small proteins to whole virus particles. Confining single isolated biomolecules in an ion trap provides a uniquely adaptable environment in which to investigate higher-order folding dynamics through manipulation of the surrounding solvent cage, temperature, and net charge at the single quantum level. We propose to optically observe these changes in folding through statistical super-resolution microscopy of different fluorescent groups. To this end we show that wavelength-scale confinement of singly-charged high-mass biomolecular ions is feasible with established trap designs using room temperature buffer gas cooling. In this regime the translational thermal motion of the ion does not contribute substantially to optical spot width. [Preview Abstract] |
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