Abstraction of sulfur atoms from carbonyl sulfide by atomic hydrogen

Abstract

The reaction of H atoms, produced by the mercury photosensitized decomposition of H2, with COS was investigated in the temperature range 27-252°. The only primary reaction of importance is H + COS -* CO + SH (1). The rate coefficient of reaction 1 was determined in competition with the reaction H + H2S -*• H2 + SH to have the value k\ = (9.1 ± 1.2) X 1012 exp((-3900 ± 370)/RT) cc mol-1 sec-1.

Ab Initio Potential Energy Surface for H + OCS Reactions: Extended Basis Sets and Correlation Treatment

“…The activation energy and pre-exponential factor reported by Tsunashima et al (1975), for rates measured between 300 to 525 K, are 3.90 ±0.370 kcal/mol and _ _ _ _ _ _ 1.5 ±0.20 x 10-11 cm 31 molecule-s. Lee, Stief, and Timmons (1977) report similar Airhenius parameters for measurements between 261 to 500 K; they give an activation energy and pre-exponential factor of 3.85 ±0.110 kcallmol and 9.06 ±1.53 x 10-12 cm 3 /molecule-s, respectively. The magnitudes of the reported pre-exponential factors are small compared to other hydrogen abstraction reactions, leading the experimentalists to conclude that A tight-activated complex was involved in the formation of product (Tsunashirna et al 1975;Lee, Stief, and Timmons 1977).…”

“…The results of the work presented here do not change those "explanations or conclusions. Unfortunately, the level of theory and basis set used in our previous study prevented us from making quantitative comparison of energetics with measured activation energies for Reaction II (Tsunashima et al 1975;Lee, Stief, and Timmons 1977).…”

“…Th7 thermal rate measurements of Tsunashima et al (1975) and Lee, Stief, and Timmons (1977) provided Arrhenius parameters for Reaction (II). The activation energy and pre-exponential factor reported by Tsunashima et al (1975), for rates measured between 300 to 525 K, are 3.90 ±0.370 kcal/mol and _ _ _ _ _ _ 1.5 ±0.20 x 10-11 cm 31 molecule-s. Lee, Stief, and Timmons (1977) report similar Airhenius parameters for measurements between 261 to 500 K; they give an activation energy and pre-exponential factor of 3.85 ±0.110 kcallmol and 9.06 ±1.53 x 10-12 cm 3 /molecule-s, respectively.…”

“…(II) range from -9.8 to -13 kcal/mol (Hfiusler, Rice, and Wittig 1987;Tsunashima et al 1975;Lee, Stief, and Timmons 1977;Hertberg 1945;lluber and llerzberg 1979;Nickolaisen 1991;Wagman et al 1982;…”

“…If one assumes, as we did in our comparisons for Reaction (1), that the critically evaluated enthalpy given by Chase et al (1985) is the most reliable number, then experimental reaction enthalpy for Reaction (II) is -12.1 ±1.2 kcal/mol. Table 5 shows that UMP2 and QCISD reaction enihalpies calculated with the 6-31 l+G(2df,2p) basis are predicted to be -8.8 kcal/mol, or 3.3 kcal/mol higher than the Chase et al (1985) value and 1.0 kcal/mol above the highest reported experimental value (Tsunashima et al 1975;Oldershaw and Porter 1972;Oldershaw and Smith 1978). However, the results from the larger "correlation consistent" basis set calculation [entry (3), Table 5] give Ali = -11.5 kcal/mol, well within the ±1.2 kcal/mel uncertainty in the Chase et al (1985) value.…”