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University of Helsinki Faculty of Science

Reaction Kinetics and Oxidation Chemistry


Contact Information

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

Group leader

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

Kinetic apparatus and method

The kinetic apparatus is designed for the kinetics of gas phase radical reactions under time-resolved conditions using a temperature-controlled tubular flow reactor. The flow reactor is coupled to a photoionization quadrupole mass spectrometer and the reactions are studied as a function of temperature and pressure. The free radicals are generated by a pulsed exciplex laser radiation from precursor molecules homogeneously along the reactor tube at low concentrations in order to isolate them from their mutual reactions in the flow reactor.

Flowing reaction mixture consists mainly of inert carrier gas (He, Ar, N2) in addition to the highly diluted precursor and reactant molecules. Therefore, only radical reactions with the selected reactant gas (e.g. O2, NO2, Cl2...) and heterogeneous wall reaction are important. The molecular reactant is added in large excess in comparison to the small initial radical concentration. Under these conditions the isolation of the radical reactions of interest is possible and reactions occur under pseudo first order conditions. Using a photoionization quadrupole mass spectrometer with a multichannel scaler (MCS), the temporal ion signal of the radical decay (as well as stable/non-reactive product formation) is obtained as a single exponential function. Consequently, direct kinetic measurements are performed to obtain absolute reaction kinetics (not relative reaction kinetics). A photo of the apparatus is shown above and a photo of the photoionization lamp construction along with a schematic figure of the apparatus are shown below. The detailed description of the method is given in the 2003 reference (Eskola, Timonen; PCCP).

Photoionization lamp construction


  • mass spectrometry
  • gas phase reaction kinetics
  • radical-molecule reactions
  • laser photolysis
  • photoionisation
  • laser photolysis photoionisation mass spectrometer (LP-PIMS)

Schematic figure of the kinetic LP-PIMS apparatus