Chapter 2
XUV Lasers for Ultrafast Electronic Control
in H 2
Alicia Palacios, Paula Rivière, Alberto González-Castrillo,
and Fernando Martín
Abstract Manipulation and control of molecular electron dynamics is currently in
the spotlight for numerous multidisciplinary applications in physics, chemistry and
biology. During the last decade, free electron lasers and sources based on high-order
harmonic generation have been successfully developed to enable the generation of
femtosecond and attosecond intense radiation pulses in the ultraviolet and soft X-ray
regions. These tools have lead to an outbreak of pump-probe experiments suited to
explore structural dynamics in atoms and molecules with spatial and temporal resolutions on the atomic length and intrinsic electronic time scales, respectively. Such
experiments, using hydrogen molecules (H 2 , D 2 ) as prototypical examples, have
been performed to study molecular dissociative single and multi-photon ionization,
photon-induced symmetry breaking in molecular dissociation, and time-resolved
imaging of coherent nuclear wave-packets. The counterpart state-of-the-art timedependent theoretical methods, able to provide a solid groundwork for describing
and interpreting the underlying ultrafast physical molecular dynamics in such experiments, are still scarce. The difficulty is to achieve an accurate description accounting for the full dimensionality of the problem. A proper treatment of nuclear
degrees of freedom is already indispensable to study multiphoton single ionization
of diatomic molecules. This is discussed in the present manuscript in different applications. We first examine the role of the coupled electronic and nuclear motions in
problems that probe coherent nuclear wave-packets using intense UV pulses and in
resonance-enhanced multiphoton single ionization (REMPI) processes, whose rates
are underestimated when using approaches within the fixed nuclei approximation.
Later, we show that for highly intense fields the presence of vibrational structure
leads to step-ladder Rabi oscillations that are probed in the REMPI probabilities.
Finally, we demonstrate the suitability of these time-dependent full-dimensional
treatments to provide time-resolved images of autoionization of H 2 , following the
A. Palacios (B) · P. Rivière · A. González-Castrillo · F. Martín
Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid, Spain
e-mail: alicia.palacios@uam.es
F. Martín
Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia),
28049 Cantoblanco, Madrid, Spain
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_2,
© Springer International Publishing Switzerland 2014
25
XUV Lasers for Ultrafast Electronic Control
in H 2
Alicia Palacios, Paula Rivière, Alberto González-Castrillo,
and Fernando Martín
Abstract Manipulation and control of molecular electron dynamics is currently in
the spotlight for numerous multidisciplinary applications in physics, chemistry and
biology. During the last decade, free electron lasers and sources based on high-order
harmonic generation have been successfully developed to enable the generation of
femtosecond and attosecond intense radiation pulses in the ultraviolet and soft X-ray
regions. These tools have lead to an outbreak of pump-probe experiments suited to
explore structural dynamics in atoms and molecules with spatial and temporal resolutions on the atomic length and intrinsic electronic time scales, respectively. Such
experiments, using hydrogen molecules (H 2 , D 2 ) as prototypical examples, have
been performed to study molecular dissociative single and multi-photon ionization,
photon-induced symmetry breaking in molecular dissociation, and time-resolved
imaging of coherent nuclear wave-packets. The counterpart state-of-the-art timedependent theoretical methods, able to provide a solid groundwork for describing
and interpreting the underlying ultrafast physical molecular dynamics in such experiments, are still scarce. The difficulty is to achieve an accurate description accounting for the full dimensionality of the problem. A proper treatment of nuclear
degrees of freedom is already indispensable to study multiphoton single ionization
of diatomic molecules. This is discussed in the present manuscript in different applications. We first examine the role of the coupled electronic and nuclear motions in
problems that probe coherent nuclear wave-packets using intense UV pulses and in
resonance-enhanced multiphoton single ionization (REMPI) processes, whose rates
are underestimated when using approaches within the fixed nuclei approximation.
Later, we show that for highly intense fields the presence of vibrational structure
leads to step-ladder Rabi oscillations that are probed in the REMPI probabilities.
Finally, we demonstrate the suitability of these time-dependent full-dimensional
treatments to provide time-resolved images of autoionization of H 2 , following the
A. Palacios (B) · P. Rivière · A. González-Castrillo · F. Martín
Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid, Spain
e-mail: alicia.palacios@uam.es
F. Martín
Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia),
28049 Cantoblanco, Madrid, Spain
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_2,
© Springer International Publishing Switzerland 2014
25