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.
References:
/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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