The present issue is a follow-up of the workshop organized by the Solvay Institutes on 2–5 May 2012, in Brussels, entitled ‘Femto-, Astro-, Spectro-Ethyne (FASE)’.
Ethyne, also named acetylene (C2H2), has attracted over the years and currently concentrates research efforts of a significant group of scientists investigating fundamental and applied topics in chemical physics, in particular.
Instrumental development in high resolution spectroscopy has relied on the regular and strong spectral pattern in acetylene as a test case, also exploiting more subtle features such as the change in geometry between the ground and first excited electronic states. As a return from the wealth of laboratory investigations from many places around the world, an unmatched vibration–rotation database has resulted in the literature. The existing information allowed very complex intramolecular mechanisms to be unravelled thanks to the building of a very efficient global Hamiltonian. Coupling schemes that were demonstrated from conventional time-independent spectroscopy made acetylene an ideal target for quantitative exploration of time-dependent, intramolecular processes. New kinds of vibrational quantum numbers and motions were demonstrated to occur, with particular insight concerning isomerization towards vinylidene. All of these fundamental developments are of direct relevance for the investigation of larger species.
Acetylene research sets as well landmarks in electronic spectroscopy of both valence and Rydberg states, also considering dissociation and ionization processes, all based on high resolution spectral information and on high level theoretical calculations. Striking developments are still on the way, e.g. to unravel the cis-trans and the acetylene-vinylidene isomerization mechanisms in excited electronic states.
Acetylene is composed of key abundant elements and present in planetary and star atmospheres, in comets and in the interstellar medium. It plays a significant role in the synthesis of major astro species and in planetary chemical cycles. It is one of the main contributors to opacities and thermal structure in stars. Quantitative spectroscopy of acetylene, including line profile and metrological state-of-the-art investigations are constantly under development to meet the needs of atmospheric and astrophysical research. High temperature partition functions and thermodynamical quantities, as well as the equilibrium geometrical structure, were determined with striking accuracy.
Aggregation of acetylene with various compounds, including acetylene itself is another subject with renewed interest within the astrophysical and planetary contexts. Overtone data are now becoming available as well as detailed information on the aggregation process, from both high resolution infrared spectroscopy and, theoretically, first principles.
Unexpected stringent astrobiological implications have even recently been suggested in the literature, calling for more consideration.
The single acetylene species thus provided a challenging basis for this international workshop, allowing access to different but complementary topics. The workshop gathered about 60 scientists and sessions were devoted to high resolution rovibrational spectroscopy, intramolecular dynamics, reactivity (in planetary atmospheres, in particular), astrochemistry, molecular complexes, and excited electronic states. Most recent, as well as review and historical results and landmarks were presented by experts in these various fields. In some cases a most exciting detective-like search of the role of acetylene was presented, from a very broad set of results or observations. It was very constructive to have the interest and expertise of different communities triggered by similar or even identical problems revealed from different backgrounds, however. This was for example the case for chemical reaction mechanisms and aerosol/dust formation occurring in planetary atmospheres and in the interstellar medium, for intramolecular coupling schemes unravelled for ground and excited electronic states, and close relations between intramolecular mechanisms in the monomer and dimers. Basic concepts such as dimerization equilibrium constant and the chemical bond were presented, also supporting the multidisciplinary and fundamental character of the meeting.
The workshop, as hoped by the organizers, turned into a very constructive and productive up to date account of the status on femto-, astro- and spectro- science in general.
The present issue gathers quite a few of the relevant topics that were discussed and illustrates the both broad and focused issues of the workshop.
The guest editor warmly thanks all contributors for their special effort towards this rich output from, and beyond the workshop, which will provide a landmark in the acetylene saga.
Further information on the workshop, including abstracts of oral and poster contributions, can be found at http://www.solvayinstitutes.be/events/FASE/fase.html