Dissociation energy of an isolated triplet acetone molecule

Abstract

The consideration of the second preequilibrium is made necessary by the finding that, in the route leading to tetrathionate, the concentrations of both thiosulfate and the hydrogen ion are on the second power.The catalytic effect of thiosulfate on the oxidation of hydrogen sulfite is explained by (M8) and (M9) I03H2S203-+ HSO3--» SO42-+ S2032" + IOf + 3H+ (M8) I03H2S203 + HSO3-+ H+ ^S042" + S2032" + I02-+ 4H+ (M9)These reactions, together with the preequilibria (M4) and (M6), are responsible for the third and the fourth terms of the rate law(1"'), resp. In this set of elementary steps, (M8) is responsible for the inhibition effect of hydrogen sulfite in the oxidation of thiosulfate, that is, for the &,[ 803~] term in the denominator of rate laws (2") and (3'). In principle, a similar inhibition effect was due to (M9). According to the experiments, however, its weight is negligible. However, due to the obvious differences in the catalytic and inhibition effects, the catalytic effect due to (M9)appears to be significant and therefore even the fourth term in (V") should have been considered.The finding that with increasing hydrogen ion concentration, and in an excess of thiosulfate, the oxidation of thiosulfate to hydrogen sulfite is suppressed in comparison with the competing oxidation to tetrathionate can be explained by ( M6) and (M7). These steps can be responsible for the &/[S2032"] [H+] term in the denominator of (3')•Of course, a great number of further reactions must occur involving iodite and hypoiodite. There are good reasons to assume that these reactions are rather complex and involve the formation of adducts between the reactants. These fast reactions, however, probably are of secondary importance in the dynamics of the system.It goes without saying that reactions M1-M9 do not represent the mechanism of the reaction. However, it seems that it is the simplest and chemically plausible set of elementary and quasielementary reactions which may be responsible for the observed phenomena.

Direct femtosecond observation of the transient intermediate in the α-cleavage reaction of (CH3)2CO to 2CH3+CO: Resolving the issue of concertedness

“…1͒. 25 Hence, the impulsive model predicts an internal energy of 38 or 45 kcal/mol for the acetyl intermediate at the two energies studied. The rotational energy of CH 3 CO is taken to be ϳ1 kcal/mol.…”

Exploring Multiple Potential Energy Surfaces: Photochemistry of Small Carbonyl Compounds

“…Photolysis of acetone is one of the most extensively studied photochemical reactions [118]. The CC bond dissociation, called "Norrish type I reaction" (CH 3 ) 2 CO → CH 3 CO + CH 3 , has been the main focus of many theoretical and experimental studies [119][120][121][122][123][124][125][126][127][128][129][130][131][132][133]. Roaming was also suggested experimentally [102], which was proposed to proceed on the S 0 PES as (CH 3 ) 2 CO → CH 3 CO · · · CH 3 → CO + CH 3 -CH 3 .…”

“…In early experimental studies [119][120][121], it was proposed that the Norrish type I dissociation occurs on the T 1 PES (the T 1 path) after an ISC from the S 1 PES, as long as the photon energy exceeds the barrier of the CC bond breaking on the T 1 PES. A theoretical calculation at the CASSCF level indicated that the ISC happens around a S 1 /T 1 -MSX structure located below the T 1 barrier, and the T 1 path was suggested to be the most preferable channel (at least in terms of potential energy) [122].…”

Ultrafast studies of the photodissociation of the acetone 3s Rydberg state at 195 nm: Formation and unimolecular dissociation of the acetyl radical

“…At wavelengths longer than 305 nm, however, vibronic structure is observed. 4,5,18 Haas and co-workers 5 report fluorescence lifetimes which decrease dramatically with shorter wavelengths near 305 nm, indicating the onset of dissociation. A barrier height of 13.2 kcal/ mole was determined.…”

“…1,4,5,[13][14][15] Evidence for a sequential dissociation from this state includes the detection of acetyl radicals and the measurement of two resolved methyl translational energy peaks. 15 For photodissociation from S 2 , the first Rydberg state, however, the experimental evidence is less conclusive and conflicting interpretations have been presented, so that questions remain concerning the photodisso-ciation mechanism.…”