by Staff Writers
Berlin, Germany (SPX) Apr 02, 2015
Using quantum chemical calculations, they were successful in interpreting the data and obtaining a detailed picture of the intermediates and reaction kinetics. The work, which has now been published in Nature, could prove helpful in developing novel catalysts for chemical storage of solar energy.
All plants do it: they store solar energy in the form of carbohydrates with the help of a metallic compound. Chemically storing sunlight would also be ideal for society's energy needs. To develop this, however, we would need to better understand exactly what happens when photons strike molecules. The primary processes run on timescales of only a few hundred femtoseconds (one femtosecond = 10-15s).
Now an international collaboration has been able to map the evolution of the chemical bonds in these kinds of ultrafast processes on the level of orbitals "We were able to determine how incident optical photons rearrange the valence electrons of a metallic carbonyl compound.
The results could help to utilise these processes in the future for more efficient conversion of sunlight into chemical energy," explains Dr. Philippe Wernet, first author of the article that has now been published in Nature.
Ballet of the valence electrons in iron pentacarbonyl
Photons cleave off a carbon monoxide so that the remaining Fe(CO)4 molecule only has 16 valence electrons making it a so called 16-electron catalyst. Such homogeneous catalysts can be potentially used in converting methane to methanol, for example.
Fe(CO)4 is highly reactive, however, only as long as it is in the singlet state. If the molecule is instead in the triplet state, it remains inert and does not form further compounds according to the laws of quantum chemistry. The study demonstrates how atom-specific probing of the frontier-orbital interactions uniquely enables correlating quantum-chemical properties of the system with its reactivity.
One year of setup, sixty hours of measurements, four years of evaluation
The experiment was set up by the PhD student Kristjan Kunnus with Philippe Wernet and the team at HZB and in collaboration with Simone Techert and her group, then at the Max Planck Institute of Biophysical Chemistry in Gottingen, now DESY and Goettingen Research Campus, who also brought in the chemistry expertise and liquid jet technology.
After characterization at BESSY II all was shipped for 60 hours measurement to the x-ray free-electron laser LCLS of the SLAC National Accelerator Laboratory in the USA. It involves what is known as a pump-probe scheme in which a very short laser pulse in the optical region excites the valence electrons of the molecule (pump), while soft X-ray pulses arrive a well-defined time delay in the femtosecond range later and probe the system for information.
Michael Odelius' team and his PhD student Ida Josefsson at the University of Stockholm modelled the compound and its excited states using quantum calculations over the following years. Only after these calculations were made could the data be interpreted to such a level of detail that the experimental observables could be unambiguously correlated with chemical interactions in the system.
"We had created basically four-dimensional data records with new coordinates of the incident energy, transferred energy as well as the intensity for various time delay between pump and probe pulses of every hundred femtoseconds", explains Kristjan Kunnus.
The measurements are a first step toward development of multidimensional X-ray spectroscopy in order to measure chemical dynamics on pulsed X-ray sources like Free Electron Lasers or BESSY-VSR. "Now that we understand the reaction kinetics, we can control them or design a system to favour desired reactions, for example, in order to chemically store solar energy", according to Wernet.
Helmholtz-Zentrum Berlin fur Materialien und Energie
Space Technology News - Applications and Research
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.|