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Rate Constants for the Decay and Reactions of the Lowest Electronically Excited Singlet State of Molecular Oxygen in Solution. An Expanded and Revised Compilation.

Francis Wilkinson
Department of Chemistry, University of Technology, Loughborough,
Leicestershire, LE11 3TU, UK
W. Phillip Helman and Alberta B. Ross
Radiation Chemistry Data Center, Radiation Laboratory, University of
Notre Dame, Notre Dame, IN 46556

J. Phys. Chem. Ref. Data 24: 663-1021 (1995)

A compilation of the reactivity of singlet oxygen, the lowest electronically excited singlet state of molecular oxygen, ¹O₂*(¹D_g), in fluid solution is presented, based on the data used in the above publication which should be consulted for clarification, expecially the introduction and indexes. Rate constants for the chemical reaction and physical deactivation of singlet oxygen available through 1994 have been compiled. Second-order rate constants for interaction of singlet oxygen with more than 1900 compounds, more than 5100 measured values, are reported.

Data Tables

Arrangement of Tables

Each table includes related groups of compounds, e.g. olefins, aromatic hydrocarbons, phenols, etc. In some cases choices were made based on functionality, for example tyrosine and its peptides are in Table 4 with phenols instead of Table 10 (amino acids and peptides). Benzopyranols (such as tocopherol) are in Table 4 (phenols) instead of Table 5 (furans and pyrans). Cysteine and methionine and their derivatives are in Table 11 (sulfur compounds), not Table 10 (amino acids).

Within each table the various substrates are arranged alphabetically by name, given an entry number which includes the table number (2_1, 2_2, etc.) and within each entry the arrangement is by solvent. Inverted names have been used as headings whenever possible so that substituted anthracenes, porphines, phenols, etc. are grouped. Systematic names have been used in most cases, otherwise, common names have been given.

Solvent

Data in each entry are grouped by solvent and listed in reverse chronological order of the year of publication. The Solvent line gives the solvent or mixture of solvents with the proportions (volume:volume). Micellar systems are labelled (mic), and the surfactant present is given in the Comment. When water or D₂O is the solvent the pH or pD is given, if reported. If the reaction was studied over a range of pH values and the k derived for a particular ionic form of the substrate no pH is given in the Solvent line. The pH is given on a line with the k or the pH range is given in the Comment line.

Rate Constants (k) and Beta (k_d/k) Values

The rate constants are generally for total quenching by chemical reaction and/or physical quenching, k = k_r + k_q. Where separate reactive quenching (k_r) and physical quenching (k_q) rate constants have been measured they are indicated in the Comment. It may be known from other studies that a particular substrate interacts with singlet oxygen totally by chemical reaction or totally by physical quenching; an example of the latter is azide ion. We have, however, only provided such data when a method was used which made the distinction. Values of b, the ratio of inverse lifetime to specific rate, k_d/k, and k_d which have been reported are also listed.

Values of k and b have been rounded to two significant figures unless they were given to only one significant figure by the authors. The authors' error limits have been omitted; when the reported error is greater than 20% the values have been given to one significant figure. Upper or lower limits have been given to only one significant figure.

Temperature

Temperatures in Kelvin are listed whenever they have been reported. When the information has not been reported it is assumed that the temperature is ambient. If the study has been carried out over a range of temperatures the range is given in the Comment line.

Introduction to Rate Constants for Singlet Oxygen.