Schedule Aug 28, 2006
Quantum Simulations of Effects of Few Cycle as to Near fs Laser Pulses on Valence Electrons: Ring Currents, Electron Circulation, and Ionization
Prof. Jörn Manz (Freie University Berlin & KITP), Mr. Ingo Barth (Freie University Berlin & KITP)

Few cycle laser pulses with durations from several hundred as to near fs may induce electronic excitations and ionizations of valence electrons in oriented molecules. For example, circularly polarized laser pulses may induce electronic ring currents or electron circulation around linear molecules such as AlCl /1/, or in ring-shaped molecules such as Mg-porphyrin /2,3,4/. These ring currents are more than hundred times stronger than traditional ones induced by permanent magnetic fields; moreover, the laser pulses allow active control, i.e. they may serve as "traffic light" for electronic pathways along alternative molecular bonds. Another example is ionization of pre-excited H2(B 1Su+) by strong laser pulses (ca 1015 W/cm2) /5/. These effects are demonstrated by movies of the laser driven electron dynamics based on the solutions of the time-dependent Schrödinger equation. For excitations of bound states, we employ simple expansions in terms of molecular electronic eigenstates. For ionization, we apply the single active electron picture (SAE) and propagate the time-dependent orbital acted on by all relevant operators (including the Coulomb and exchange operators, beyond previous effective operators), by extension of the method of Paramonov /6/. The emerging picture yields several details beyond the traditional three step model of Corkum /7/, i.e. the rather "violent" ionization yields the generation and separation of many lobes of the wavepacket which are shaken away, until the remaining "naked" H2+ recollects part of the ionized electron back to the original orbital. We also discuss extensions including a hierarchy of methods for additional time-dependent electrons in complete active states TD-CAS.

We hope that our presentation will stimulate fruitful discussions on the experimental discovery of the predicted effects, and extensions of the theoretical techniques.

We would like to express our gratitude to all co-authors /1-5/. Financial support by Deutsche Forschungsgemeinschaft (project Ma 515/23-1) and Fonds der chemischen Industrie is also gratefully acknowledged.


/1/ I. Barth, J. Manz, L. Serrano-Andrés, in preparation (AlCl)
/2/ I. Barth, J. Manz, Y. Shigeta, K. Yagi, J. Am. Chem. Soc. 128, 7043 (2006)
/3/ I. Barth, J. Manz, Angew. Chem. Int. Ed. 45, 2962 (2006)
/4/ I. Barth, J. Manz, in: Femtochemistry VII: A Conference Devoted to
Fundamental Ultrafast Processes in Chemistry, Physics, and Biology,
W. A. Castleman, M. L. Kimble (Eds.), Elsevier, Amsterdam (2006), in press
/5/ I. Barth, L. González, J. Manz, G. K. Paramonov, in preparation (H2)
/6/ G. K. Paramonov, Chem. Phys. Lett. 411, 350 (2005)
/7/ P. B. Corkum, Phys. Rev. Lett. 71, 1994 (1993)

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