University homepage In English
University of Helsinki Faculty of Science
 

Reaction Kinetics and Oxidation Chemistry

Menu

Contact Information

Laboratory of Physical Chemistry
Department of Chemistry
A.I. Virtasen aukio 1
(P.O. BOX 55)
FI-00014 University of Helsinki
Finland

Group leaders

Academy research fellow
Arkke Eskola, Ph.D.
Phone: +358 2941 50288
e-mail: arkke.eskola (AT) helsinki.fi



Research Directions

While the research interests of the group focus on free radical reaction kinetics and oxidation chemistry in gas-phase, the group has several research directions (i.e. research interest subdivide into several research directions). Our kinetic apparatus is a unique instrument which has up to date applied to investigate radical chemical reactivity (employing R + Cl2 and R + NO2 reactions), radical thermochemistry (R + HBr reactions), importance of H-atom tunneling in radical reactions (CH3/CD3 + HCl/DCl reactions), and reactions of radicals with molecular oxygen O2; R + O2 reactions are important almost everywhere on Earth, from atmosphere to combustion. Interestingly, our study on CH2I + O2 and CH2Br + O2 reactions from year 2006 (PCCP (2006), 8 (12), 1416-1424), where we observed remarkably different behavior between these two reactions, was crucial initiator for the first direct observation of Criegee intermediate (SCIENCE (2012), 335 (6065), 204-207). See also Physics Today (2012), 65 (3), 17-19 about the story how the smallest Criegee intermediate, CH2OO, was observed for the first time. This scientific breakthrough, where our group played an important role, has then led to very many high-impact publications and greatly changed our view of importance Criegee intermediates play in atmospheric chemistry. Below are some of our previous and current research directions.

Atmospheric chemistry. Important research direction is investigation of R + O2 reactions, which at low temperatures (T ≈ - 85 C - 40 C) are relevant to atmospheric chemistry. We have measured kinetics of several alkyl, alkenyl, and resonantly stabilized alkenyl radical reactions with molecular oxygen. In addition, we have studied reactions of nitrogen containing alkyl radicals (e.g. CH2NH2, CH3CHNH2) with O2, which atmospheric relevance has recently increased significantly because these radicals are formed in atmospheric degradation of compounds that are used, or are planned to be used, in carbon-capture process of CO2 from flue gases of power stations. Since there is always some release of amine compounds into atmosphere from carbon-capture process, it is important to understand their degradation compounds which might be harmful, if not toxic. We have also studied hydrogen-atom tunneling by measuring kinetics of CH3 + HCl → CH4 + Cl reaction (with all H/D combinations) over wide temperature range.

Combustion chemistry. R + O2 reactions are crucial also under combustion conditions, of course. Already at 400 - 800 K temperatures peroxy-radicals RO2 become thermally unstable and often decompose back to R + O2. For this reason also other reactions of radical R become important. Consequently, we have studied kinetics of several R + NO, R + NO2, and R + Cl2 reactions. Chlorinated alkyl radicals and molecular chlorine, for example, are intermediates in combustion of municipal waste in incinerators. Resonantly-stabilized radicals (e.g. allyl (C3H5) and propargyl (C3H3) radicals), on the other hand, react very slowly with O2 at higher temperatures (T > 500 K), which, also due to their high thermal stability, results in significant soot formation tendency from their self- or mutual reactions, e.g. C3H3 + C3H3 reactions. Soot formation is probably the most significant problem in diesel engines. Also, since NO and NO2 are always present under combustion conditions, both R + NO and R + NO2 reactions play important role for example during diesel engine combustion.