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1.
Phys Rev Lett ; 110(16): 163001, 2013 Apr 19.
Artículo en Inglés | MEDLINE | ID: mdl-23679597

RESUMEN

We have observed single photon double K-shell photoionization in the C(2)H(2n) (n=1-3) hydrocarbon sequence and in N(2) and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the K(-2) process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (K(-1)K(-1) process). In the C(2)H(2n) sequence, the spectroscopy of K(-1)K(-1) states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single K-shell ionization. The cross section variation for single photon K(-1)K(-1) double core ionization in the C(2)H(2n) sequence and in the isoelectronic C(2)H(2n), N(2) and CO molecules validates a knock-out mechanism in which a primary ionized 1s photoelectron ejects another 1s electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.

2.
Phys Rev Lett ; 107(19): 193004, 2011 Nov 04.
Artículo en Inglés | MEDLINE | ID: mdl-22181603

RESUMEN

We observe the formation in a single-photon transition of two core holes, each at a different carbon atom of the C2H2 molecule. At a photon energy of 770.5 eV, the probability of this 2-site core double ionization amounts to 1.6 ± 0.4% of the 1-site core double ionization. A simple theoretical model based on the knockout mechanism gives reasonable agreement with experiment. Spectroscopy and Auger decays of the associated double core hole states are also investigated.

3.
J Chem Phys ; 128(11): 114317, 2008 Mar 21.
Artículo en Inglés | MEDLINE | ID: mdl-18361581

RESUMEN

Gerade-ungerade symmetry breaking in HD for the bound states supported by the shallow outer I' (1)Pi(g) potential is studied theoretically. By clarifying the asymptotic behavior of the relevant nonadiabatic couplings among the stats correlating to the n=2 dissociation limit, simple two-state (for f-parity) and three-state (for e-parity) approximations are formulated. They reproduce binding energies in very good agreement with recent spectroscopic measurements. Comparisons with the calculations based on a single model potential are presented and the dependence of the results on the used ab initio Born-Oppenheimer (clamped nuclei) potentials is discussed.

4.
J Chem Phys ; 126(3): 034310, 2007 Jan 21.
Artículo en Inglés | MEDLINE | ID: mdl-17249874

RESUMEN

The authors investigate the use of absorbing potentials and discrete variable representation grid methods in multichannel time-independent scattering calculations. An exactly solvable, coupled-two-channel problem involving square-well potentials is used to assess the quality of numerical results. Special emphasis is given to the description of scattering resonances and near-threshold regions. Numerical treatment of close vicinities of thresholds requires the introduction of nonequidistant grids through a mapping procedure of the scattering coordinate.

5.
J Chem Phys ; 124(9): 94303, 2006 Mar 07.
Artículo en Inglés | MEDLINE | ID: mdl-16526853

RESUMEN

We investigate the use of complex absorbing potentials for the calculation of partial cross sections in multichannel photofragmentation processes. An exactly solvable, coupled-two-channel problem involving square-well potentials is used to compare the performance of various types of absorbing potentials. Special emphasis is given to the near-threshold regions and the conditions under which the numerical results are able to reproduce the Wigner threshold laws. It was found that singular, transmission-free absorbing potentials perform better than those of power or polynomial form.

6.
J Chem Phys ; 122(4): 44108, 2005 Jan 22.
Artículo en Inglés | MEDLINE | ID: mdl-15740236

RESUMEN

We combine the Lanczos algorithm with the absorbing-potential method, implemented in a discrete variable representation to calculate the near-threshold photodissociation cross sections of CH+. The method is iterative, based on a continued fraction representation of the Green function and avoids any explicit matrix diagonalization. A very good agreement is found with experiment and close-coupling calculations.

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