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Physical and Biophysical Chemistry Division (I)


Number: 2003-024-1-100

Title: Selected free radicals and critical intermediates: thermodynamic properties from theory and experiment

Task Group
: Branko Ruscic

Members: Tibor Bérces, J. E. Boggs, A. Burcat, A. Császár, J. Demaison, R. Janoschek, J.M.L. Martin, M. J. Rossi, J. Stanton, P. Szalay, P.R. Westmoreland, and F. Zabel

The main objective of this project activity is the continued compilation and critical evaluation of published thermodynamic properties, including the computation of accurate thermochemical data for selected free radicals, that are of importance in atmospheric and combustion chemistry. A distinguishing feature of the critical data evaluation is the systematic utilization of all available kinetic, spectroscopic and ion thermochemical results as well as high-level computations.

Knowledge of accurate thermochemical properties of free radicals is of great importance in many branches of chemistry, in particular atmospheric and combustion modeling. Thermochemical kinetic estimations provide sometimes the only possibility for obtaining rate coefficients and branching ratios for reactions of short-lived intermediates such as free radicals. Thermodynamic quantities for stable molecules are relatively well established. These are typically obtained from calorimetric determinations, while heat capacities and entropies are derived from the results of spectroscopic measurements. For free radicals and other short-lived intermediates, direct calorimetric measurements are (in most cases) not possible, while spectroscopic investigations require more skill and sophisticated instrumentation. Consequently, thermochemical data for a number of free radicals have a higher uncertainty than the corresponding values of closed shell species. However, computational chemistry has made great progress in reliability and accuracy. A solid basis of thermochemistry now comprises the optimized combination of experimental and computational results.

Such type of work has been initiated in our IUPAC project 2000-013-1-100 which comes to a preliminary conclusion at the end of the year 2003. Within this project the critical evaluation of thermodynamic properties of 36 free radicals has been carried out.

The success of this work so far suggests an extension of data evaluation beyond the initial goal to cover an increased number of key radicals that play important part in atmospheric chemistry and combustion. This requires the development of datasheets for about 25 further radicals.

extension of project #2000-013-1-100

This project was presented at a poster session at the IUPAC Congress/GA August 2007
>view pdf - 1.00MB<

July 2005 - A substantial part of the work has been completed and 12 papers have appeared or are in press during 2004-05. Additional papers are being written as the work progresses. While the scope of this project was originally targeted to perform a systematic critical evaluation of the thermochemistry of important radicals, the scientific problems that are being encountered and formulated as the evaluation effort progresses, have become a unique spiritus movens, motivating ground-breaking research and development of new general methods. This is especially the case in the areas of electronic structure calculations (W3 and HEAT), and of dealing efficiently with complex interrelationships inherently present in thermochemistry (ATcT).

The following publications have appeared from this project:

- Thermochemical Properties of the Hydroxy-formyl Radical HO CO, and the Formyloxy Radical, HC(O)O, and their Role in the Reaction OH + CO .H + CO2: Computational G3MP2B3 and CCSD(T)-CBS Studies
W. M. F. Fabian and R. Janoschek. J. Mol. Struct. TheoChem 713, 227 (2005)

- Ab Initio Determination of the Heat of Formation of Ketenyl (HCCO) and Ethynyl (CCH) Radicals.
P. G. Szalay, A. Tajti, and J. F. Stanton. Mol. Phys. 103, 2159-2168 (2005)

- IUPAC Critical Evaluation of Thermochemical Properties of Selected Radicals: Part I.
B. Ruscic, J. E. Boggs, A. Burcat, A. G. Császár, J. Demaison, R. Janoschek, J. M. L. Martin, M. L. Morton, M. J. Rossi, J. F. Stanton, P. G. Szalay, P. R. Westmoreland, F. Zabel, and T. Bérces. J. Phys. Chem. Ref. Data 34, 573-656 (2005)
> on-line abtract on the JCPRD website

- Pulsed Field Ionization Photoelectron-photoion Coincidence Study of the Process N2 + h . .N + + N + e - : Bond Dissociation Energies of N2 and N2 +
X. Tang, Y. Hou, C. Y. Ng, and B. Ruscic. J. Chem. Phys. 123, 074330/1-7 (2005)

This project was presented at a poster session at the IUPAC Congress/GA July 2005
>view pdf - 534KB<

- Thermochemical Properties of Free Radicals from G3MP2B3 Calculations, Set-2: Free Radicals with Special Consideration of CH2=CH-C=CH2, cyclo-C5H5, CH2OOH, HO-CO, and HC(O)O.
R. Janoschek and M. J. Rossi. Int. J. Chem. Kinet. 36, 661 (2004)

- W3 Theory: Robust Computational Thermochemistry in the kJ/mol Accuracy Range.
A. D. Boese, M. Oren, O. Atasoylu, and J. M. L. Martin. J. Chem. Phys. 120, 4129 (2004)

- Benchmark Thermochemistry of the Hydroperoxyl Radical.
B. A. Flowers, P. G. Szalay, J. F. Stanton, M. Kállay, J. Gauss, and A. G. Császár. J. Phys. Chem. A 108, 3195 (2004)

- Vibrational Spectrum and Thermochemistry of the Formyl (HCO) Radical: A Variational Study by the Coupled Cluster CCSD(T) Method with Complete Basis Set Extrapolation.
A. V. Marenich and J. E. Boggs. J. Phys. Chem. A 108, 5431 (2004)

- Thermodynamic Properties of C1 and C2 Bromo Compounds and Radicals: A Relativistic ab Initio Study.
M. Oren, M. A. Iron, A. Burcat, and J. M. L. Martin. J. Phys. Chem. A 108, 7752 (2004)

- Introduction to Active Thermochemical Tables: Several “Key” Enthalpies of Formation Revisited.
B. Ruscic, R. E. Pinzon, M. L. Morton, G. Von Laszevski, S. J. Bittner, S. G. Nijsure, K. A. Amin, M. Minkoff, and A. F. Wagner. J. Phys. Chem. A 108, 9979 (2004)

- B. Ruscic
Active Thermochemical Tables in: 2005 Yearbook of Science and Technology, McGraw-Hill, New York, 2004, pp. 3-7

- Equilibrium Geometry of the Ethynyl (CCH) Radical.
P. G. Szalay, L. S. Thøgersen, J. Olsen, M. Kállay, and J. Gauss. J. Phys. Chem. A 108, 3030 (2004)

- HEAT: High Accuracy Extrapolated Ab Initio Thermochemistry.
A. Tajti, P. G. Szalay, A. G. Császár, M. Kállay, J. Gauss, E. F. Valeev, B. A. Flowers, J. Vázquez, and J. F. Stanton. J. Chem. Phys. 121, 11599 (2004)

- Enthalpy of Formation of 2 . 3/2 SH.
A. G. Császár, M. L. Leininger, and A. Burcat. J. Phys. Chem. A 107, 2061 (2003)

- Equilibrium Structure and Force Field of NH2.
J. Demaison, L. Margulès, and J. E. Boggs. Phys. Chem. Chem. Phys. 5, 3359 (2003)

- Structural and Thermochemical Properties of the Hydroxymethyl (CH2OH) Radical: A High Precision Ab Initio Study.
A. V. Marenich and J. E. Boggs. J. Chem. Phys. 119, 10105 (2003)

- Coupled Cluster CCSD(T) Calculations of Equilibrium Geometries, Anharminic Force Fields, and Thermodynamic Properties of the Formyl (HCO) and Isoformyl (COH) Radical Species.
A. V. Marenich and J. E. Boggs. J. Phys. Chem. A 107, 2343 (2003)

- A Variational Study of Nuclear Dynamics and Structural Flexibility of the CH2OH Radical.
A. V. Marenich and J. E. Boggs. J. Chem. Phys. 119, 3098 (2003)

- Thermochemical Properties of Free Radicals from G3MP2B3 Calculations.
R. Janoschek and M. J. Rossi. Int. J. Chem. Kinet. 34, 550 (2002)

- The Enthalpy of Formation of 2 . CH.
A. G. Császár, P. G. Szalay, and M. L. Leininger. Mol. Phys. 100, 3879 (2002)

- Anharmonic Force Field, Structure, and Thermochemistry of CF2 and CCl2.
J. Demaison, L. Margulès, J. M. L. Martin, and J. E. Boggs. Phys. Chem. Chem. Phys. 4, 3282 (2002)


Last update: 24 August 2007



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