Role of intersystem crossing in the reactive scattering of O( 3P) atoms with CH 2I 2 molecules

Reaction of O(3P) with the alkyl iodides: CF3I, CH3I, CH2I2, C2H5I, 1-C3H7I and 2-C3H7I

“…The data for O( 3 P) þ CH 2 I 2 does not fit well with this trend, possibly reflecting stabilisation of the association complex via involvement of two iodine atoms. 1 The rate coefficients obtained at 298 K can be compared to data obtained for the reactions of the same RI with both the OH radical and Cl atoms, which are also listed in Table 3. With the exception of CH 2 I 2 (for which no rate coefficients for reaction with Cl or OH are available) some interesting trends are observed.…”

“…Interest in the reactions of alkyl iodides (RI) with oxygen atoms (O( 3 P)) stems from a desire to understand the mechanism of these processes, which have multi-channel product pathways on singlet and triplet potential energy surfaces and which involve the initial formation of a R-I-O complex. [1][2][3][4][5] Whereas IO elimination is the most important product channel for the smallest iodoalkanes, CH 3 I and CF 3 I (e.g., F(IO) % 0.8-0.9 for CF 3 I), 6 the presence of a b-position C-H bond in the longer chain iodoalkanes enables the intramolecular abstraction of an H-atom via a five-membered transition state to eliminate HOI with a yield as high as %0.8 for e.g., O( 3 P) þ C 2 H 5 I. 7 The formation of HOI in a spin forbidden process has been used as a laboratory source of HOI, as has the spin allowed formation of IO and R 0 .…”

Dynamics of the O(3P) + C2H2 reaction from crossed molecular beam experiments with soft electron ionization detection

“…Previous measurements of the reactive scattering of O( 3 P) with various alkyl iodides have indicated the occurrence of ISC. [25][26][27] Nevertheless, the investigation of atomic oxygen reactions with small molecules containing light atoms, such as O + H 2 S, clearly excluded the occurrence of ISC, 28 39 42 AE 10 58 AE 10 Michael and Wagner (1990) (900-1200 K) 19 80 AE 15 Boullart and Peeters (1992) (290 K) 20 85 +4 so leading to the conclusion that ISC could be significant only in the presence of heavy atoms because of the larger spin-orbit coupling. In this respect, it came as a surprise that for the reaction O( 3 P) + C 2 H 4 ISC accounts for about 50% of the total reactivity, [29][30][31] and even more for the reactions O( 3 P) + CH 2 CCH 2 (allene) 32 and O( 3 P) + CH 3 CCH (methylacetylene).…”

Direct Observation of Spin Forbidden Proton-Transfer Reactions: 3NO- + HA → 1HNO + A-

“…We report a set of reactions in the gas phase in which the proton-transfer rate is measurable but slow because they require a spin change in order to convert to products. − These reactions have very different kinetic constraints than reactions with conventional energy barriers. The results reported here demonstrate the importance of structure-dependent dynamics as well as energetics in determining the overall consequences of spin conversion.…”