The advances in recent years in the field of molecular dynamics
are numerous and impressive. In sophisticated experimental and theoretical
studies it is nowadays possible to steer chemical reactions with
quantum-number-prepared molecules, to study reaction products fully
state-specifically, and to derive accurate potential energy surfaces with
the goal of determining the pathways along which molecular interaction can
take place. Both experimental and theoretical techniques have rapidly
improved, and our understanding of the dynamical nature of chemical
processes is continuously growing.
In this special issue of CAMOP/Physica Scripta we have tried to
present a snapshot of the state-of-the-art in the field of molecular
dynamics. It contains a collection of papers submitted in association with
the most recent MOLEC meeting (MOLEC XV) held in September 2004 in
Nunspeet, The Netherlands. This biannual meeting started in 1976 in Trento
and was subsequently organized in Brandbjerg Højskole (Denmark, 1978),
Oxford (UK, 1980), Nijmegen (The Netherlands, 1982), Jerusalem (Israel,
1984), Aussois (France, 1986), Assissi (Italy, 1988), Bernkastel-Kues
(Germany, 1990), Prague (Czech Republic, 1992), Salamanca (Spain, 1994),
Nyborg Strand (Denmark, 1996), Bristol (UK, 1998), Jerusalem (Israel, 2000)
and Istanbul (Turkey, 2002). Within the philosophy of CAMOP we have asked
invited speakers to report on outstanding problems in their particular
field. This comprises discussion of open questions, important applications,
new theoretical and experimental approaches and also predictions of future
developments. A good comment, in addition to being an authoritative
contribution of an acknowledged expert, should also be readable by the
non-expert and we have taken special care that the work presented here is
introduced in an understandable way and has been placed within the context
of accessible literature for the interested reader.
The sequence of 16 papers that is presented in this issue is arranged
according to three main topics that form a focus within the field and can
be roughly summarized as induced chemical (intermolecular) dynamics,
molecular spectroscopy/theory, and photo-induced uni-molecular
(intramolecular) dynamics.
The issue opens with a contribution by the MOLEC XV award winner Levine and
his co-workers (the paper by Kornweitz et al) in which they speculate
on the possibility of probing electronic rearrangement in a chemical
collision using light emitted during the very collision. Banares and
co-workers continue with an overview on what is and what is not understood
about the dynamics of the `most simple reaction' H + H2 and prospects
for future research of this prototypic system are presented. The effect of
molecular structure on chemical dynamics is discussed by Pearce et al on
the example of HCl originating from Cl atoms reacting with different
organic ethers. Stereodynamical effects are discussed by Cappelletti and
co-workers starting from collisional alignment in supersonic seeded
molecular beams with applications ranging from (in)elastic events to
selective surface scattering experiments. A laboratory controlled study of
chemical reactions under interstellar conditions using temperature variable
multi-electrode traps is reviewed by Gerlich and Smith. Eritt et al discuss
a technique capable of studying the interaction of electrons with size
selected molecular ions and results are presented for the electron
detachment of Cn- and Aln-clusters. Ultrafast dynamical events at a conical intersection are discussed in a theoretical study by Burghardt et al and
the experimental tools to study electron dynamics are presented by Vrakking in a contribution on direct and
indirect methods to generate attoseconds.
In four spectroscopic and theoretical contributions the latest findings are
presented in interpreting and understanding complicated molecular spectra.
Meerts and Smit introduce a powerful numerical assign and analysis method
based upon genetic algorithms and its performance is demonstrated on the
example of dense spectra of (complexed) aromatic species. Interaction
potential surface calculations of rare gases with halogens in van der
Waals complexes are described by Delgado-Barrio and co-workers, and
Tennyson discusses new theoretical techniques based on the use of the
variational principle to guide the spectral assignment of complicated water
spectra, e.g. at very high temperatures. Finally, Okumura and co-workers
present NIR spectra of NO3 and in combination with new calculations
these shed light on how to interpret vibronic couplings in this interesting
system.
The last section of this issue comprises fragmentation and
photo-dissociation studies. Rubio-Lago et al discuss methods to produce
high-density spin polarized hydrogen following photodissociation
experiments. The photodissociation of HCl and Cl2 is taken as an example
by Balint-Kurti et al to demonstrate how amplitudes and phases of the
photofragmentation matrix elements are derived from experimental
measurements. Directional dynamics in photodissociation processes and the
derivation of molecular frame properties are discussed in detail by Van den
Brom et al using laboratory oriented molecules. And the issue closes with a
contribution by Chambreau et al on different reaction mechanisms in the
photodissociation of formaldehyde into H2 and CO.
Coming to the end of this editorial, we wish to thank all the authors who
participated with their contributions in this issue. It shows what is
possible nowadays in the field of molecular dynamics and where things are
heading in the near future. We thank Physica Scripta for providing us
with the platform for this Special Issue, and we wish you, dear reader,
many new insights!
Steven Solte, Vrije Universiteit Amsterdam, The Netherlands
Harold Linnartz, Leiden Observatory, The Netherlands