Potential Energy Surfaces for the Reaction of O Atoms with CH₃I:  Implications for Thermochemistry and Kinetics

Abstract

The geometries of IO, HCIO, ICH 2 O, CH 3 IO, CH 3 OI, CH 2 IOH, and ICH 2 OH have been obtained at the HF and MP2(FU)/6-31G(d) levels of ab initio theory, and the HF/6-31G(d) frequencies are compared with experimental assignments where these are available. The Gaussian-2 method was used to provide thermochemical data for use in atmospheric and combustion modeling. Transition states that connect these species have also been characterized, and the results were used to develop the singlet and triplet potential energy surfaces for the reaction O( 3 P) + CH 3 I. These surfaces explain the complex behavior of this reaction, and a QRRK analysis over 200-2000 K gave good accord with recent kinetic and product studies by Gilles et al. [J. Phys. Chem. 1996, 100, 14005]. IO is predicted to be the dominant product below about 2000 K. Other likely products are OH and the collisionally stabilized adducts CH 3 IO and ICH 2 OH, and the latter's fragmentation products that include H and HI.

Computational investigation of isomeric and conformeric structures of methyl iodoperoxide

“…Thus, the C-I bond distances in CH 2 IOOH and ICH 2 OOH were found to be 1.958 and 1.929 Å, and 2.201, and 2.162 Å, with basis sets A and B, respectively. The results are consistent with the CH 2 IOH and ICH 2 OH cases (12) where the values 1.959 and 2.225 Å have been determined, respectively, at the MP2/6-31G(d) level. The partially double C-I bond is also demonstrated by the slight biradical character that the molecule appears to possess as reflected in the instability of the spin-restricted (RHF) wavefunction compared to the spin-unrestricted (UHF) one (12).…”

“…It is the methyl analog of hydrogen iodoperoxide (HOOI) recently investigated theoretically (10) and similarly involved in the mechanism of HO + IO reaction (11). Other related systems include the isomeric forms of methyl hypoiodide (CH 3 OI, CH 3 IO, and ICH 2 OH), extensively studied in the work of Misra et al (12) where the novel species CH 2 IOH has been computed at the MP2 level of theory that has no counterpart in the chemistry of lighter halomethanes.…”

Crossed beam studies of the O(3P,1D)+CH3I reactions: Direct evidence of intersystem crossing

“…(6) Complex formation takes place via intersystem crossing. As shown by Misra et al, 15 ISC is most probable in the entrance channel at an OÈI distance of B2.3 and a bent OÈIÈC conÐgu-A ration of 109¡, for which the potential energy is equal to B30 kJ mol~1. Using the angular E 0 dependent line of center (ADLOC) model,50 a reasonable estimation of the opacity function can then be made, from which a distribution of the orbital angular momentum consistent with complex formation is deduced.…”

A discharge–flow study of the kinetics of the reactions of IO with CH3O2 and CF3O2

“…Thermodynamic data for heats of formation were gathered from the IUPAC review 18 except for CH 3 OI, 30 CH 2 O 2 31 and HOOI (estimate of D f H 298 ¼ 16 kJ mol À1 determined by our own PM3 calculation). Determination of product channels was not the primary objective of our study (and the techniques employed are not suitable for a detailed examination of the species liberated), but certain information was obtained.…”