Role of Renner Teller and Spin−Orbit Interaction in the Dynamics of the O(³P) + CH₂ICl Reaction

Abstract

Reactive scattering of O(3P) atoms with CH2ICl molecules has been measured at initial translational energies E ∼ 46 and 17 kJ mol-1 using a supersonic beam of O atoms seeded in He and Ne buffer gases generated from a high-pressure microwave discharge source. At the higher initial translational energy, the IO product scattering can be resolved into two components; one showing forward and backward peaking with a product translational energy distribution peaking at low energy with a tail extending out to higher energy, and the other that peaks in the backward direction with higher product translational energy. At lower initial translational energy, the IO product scattering does not allow the resolution of two components but peaks in the backward direction with a higher product translational energy than for scattering in the forward hemisphere. The slow component is attributed to dissociation of a long-lived OICH2Cl complex formed by intersystem crossing from the initial triplet 3A‘‘ potential energy surface to the underlying singlet 1A‘ potential energy surface. The fast component is attributed to direct reaction over the triplet potential energy surface with the sharp backward peaking arising from reaction on the 3Π2 and 3Π1 spin multiplet surfaces in near collinear OICH2Cl configurations and the scattering in the sideways and forward directions arising from reaction on the 3A‘‘ Renner Teller surface in strongly bent configurations. The contribution of the slow component is approximately one-third that of the fast component to the total reaction cross section for IO product scattering.

CROSSED-BEAM STUDIES OF REACTION DYNAMICS

“…The late Roger Grice's group in Manchester carried out a great deal of work on a variety of F, Cl, and O( 3 P) reactions (217)(218)(219)(220)(221), as well as some studies of radical reactions such as CH 3 + I 2 (185) and OD + Br 2 (222). A new CMB apparatus has been built at Cornell, and studies of transition metal reaction dynamics have been ?…”

“…Special mention goes to the studies carried out in Berkeley of O( 3 P) with acetylene (205) and ethylene (206), in which the branching ratios and the dynamics of both relevant reaction channels leading to HCCO + H and CH 2 + CO, and CH 2 CHO + H and CH 3 + CHO, respectively, were characterized. In Manchester, particular attention has been devoted to the role of ISC in O( 3 P) reactions with halogen and interhalogen molecules, and with alkyl iodides (218)(219)(220)(221). A peculiarity of O( 3 P) reactions is that reactants approach on a triplet PES that intersects a singlet PES that usually supports a stable intermediate: ISC is then possible from the triplet to the singlet PES, making the dynamics that involve motion on the underlying PES different from those that involve motion only over the triplet PES.…”

“…In Manchester, particular attention has been devoted to the role of ISC in O( 3 P) reactions with halogen and interhalogen molecules, and with alkyl iodides (218)(219)(220)(221). Recent measurements of the reactive scattering of O( 3 P) with various alkyl iodides have indicated the occurrence of this ISC (220,221). Recent measurements of the reactive scattering of O( 3 P) with various alkyl iodides have indicated the occurrence of this ISC (220,221).…”

Infrared chemiluminescence: Evidence for adduct formation in the H + CH2XI reaction and studies of the N + CH2X (X = Cl/F/I/H) reactions

“…Reactions of O atoms 13 and Cl atoms 12 with CH 2 ClI appear to proceed via bound intermediates. Leone and co-workers 14 have shown that the mechanism for O þ C 2 H 5 I and larger alkyl iodides involves a bound intermediate that gives HOI.…”

“…8 Major sources for I atoms in the atmosphere are CH 3 I and CH 2 ClI. 8 Photodissociation of these iodocompounds 9,10 and their reactions with Cl 11,12 and O 13 atoms have been studied as possible sinks for CH 2 ClI in the atmosphere. As pointed out above, H atoms rapidly react with iodoalkanes and the H atom reaction could also be an important sink for CH 2 ClI.…”