Vol. 23, No.5
Free Radicals and Critical Intermediates: Thermodynamic Properties from
Theory and Experiment
Accurate thermodynamic data are required in modeling of atmospheric
processes, combustion, and other complex chemical systems. However,
for most of the free radicals participating in such processes, no reliable
thermodynamic properties are available; literature data are contradictory,
often depend on a single determination made decades ago using indirect
methods, or are based on estimations. Owing to the progress made in
developing new direct experimental techniques, reliable thermodynamic
properties have become available for more and more free radicals. In
spite of this success, a breakthrough and an essential improvement in
this field may not be expected in the near future. Fortunately, recent
studies using ab initio theoretical methods have shown that an accuracy
better than 4 kJ/mol is a realistic aim in the computation of enthalpies
This analysis of the state of affairs was the motivation that initiated
a joint effort of experimentalists and theoreticians to create a set
of reliable thermodynamic properties for selected organic free radicals.
IUPAC has approved a 2.5-year project for the compilation and critical
evaluation of available thermodynamic properties as well as for the
computation of accurate data for selected free radicals that are of
importance in atmospheric chemistry and/or combustion. Altogether, six
experimentalists and seven theoreticians are participating in the project.
The interdisciplinary character of this group may prove to be useful
in finding the right answer in cases where contradictory thermodynamic
properties were published for the same free radical from different laboratories
or were obtained by different techniques.
A series of seminal papers, to be published in leading journals of
physical chemistry and chemical physics, is expected from this project.
The final results of the project will appear in peer-reviewed journals
such as the Journal of Physical and Chemical Reference Data or Pure
and Applied Chemistry. A web version of the results may be presented
in the NIST Chemistry Web Book.
It is expected that the recommended thermodynamic data, the results
of compilation and critical data evaluation of organic free radicals,
would be widely used by the kineticist community. The major users are
probably the modelers dealing with atmospheric chemistry and/or combustion.
The anticipated impact is an improvement in the reliability of the predictions
of modeling studies. Comments from the chemistry community are welcome
and should be addressed to the task group chairman, Prof. Tibor Bérces,
Institute for Chemistry, Chemical Research Center, Hungarian Academy
of Sciences, Pusztaszeri u. 59/67, H1025 Budapest, Hungary; Tel: 36
1 325 7752; Fax 36 1 325 7554; E-mail: email@example.com.
projects/2000/2000-013-1-100.html for project description and update.