Role of Renner Teller and Spin−Orbit Interaction in the Dynamics of the O(³P) + C₃H₅I Reaction

Abstract

Reactive scattering of O(3P) atoms with C3H5I molecules has been studied at initial translational energies E ∼ 46 and 16 kJ mol-1 using a supersonic beam of O atoms seeded in He and Ne buffer gas generated from a microwave discharge source. Strongly backward peaked angular distributions of IO product scattering are observed at both initial translational energies with the peaking becoming sharper at higher energy. The product translational energy distributions are pitched at higher energy for the backward scattering and shift progressively toward lower energy as the IO scattering moves round into the forward direction. Backward scattering with high product translational energy is attributed to direct reaction in small impact parameter collisions b ≤ 2.5 Å over the triplet potential energy surface. Scattering with low product translational energy which becomes perceptible in the forward direction is attributed to intersystem crossing to the underlying singlet potential energy surface forming a bound OIC3H5 intermediate complex. Direct reaction over the 3A‘‘ potential energy surface plays a more significant role for the exoergic allyl iodide reaction than in the nearly thermoneutral reactions of alkyl iodide molecules, where intersystem crossing to the 1A‘ potential energy surface is the predominant reaction mechanism. The dynamical basis for this difference in mechanism is discussed in terms of the topography of the potential energy surfaces involved.

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

“…9 of ref. 28) indicate that the most favorable channel should be that leading to IO(2% 3@2 ) However, nonadiabatic coupling may readily take place in the exit channel in this ] CH 3 (2A 2 A). multisurface system containing the heavy iodine atom, as already observed in the reaction O(1D) ] HCl ] ClO(2% 3@2,1@2 ) ] H.54 The signiÐcant polarization of the symmetric c.m.…”

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

“…(2) the absence of spin-orbit interaction, the 3 Π potential energy surface splits into an upper 3 A′ surface, which favors the collinear configuration and a lower 3 A′′ surface which favors bent configurations. However spin-orbit interaction splits the 3 Π surface into spin multiplet components 3 Π 2 , 3 Π 1 , 3 Π 0 + , 3 Π 0in the collinear configuration and in bent configurations the symmetries of the spin multiplet components are denoted by a′ and a′′.…”

“…Recent crossed molecular beam studies − of the reactive scattering of ground-state O( 3 P) atoms with alkyl and allyl iodide molecules have shown the importance of intersystem crossing from the initial triplet potential energy surfaces to the underlying singlet potential energy surface. Direct dynamics over the triplet potential energy surface result in IO product formed with high translational energy, whereas the singlet potential energy surface supports a long-lived OIR intermediate complex that yields IO product with low translational energy and in some cases ,,, HOI product formed via a five-membered ring transition state.…”

“…Direct dynamics over the triplet potential energy surface result in IO product formed with high translational energy, whereas the singlet potential energy surface supports a long-lived OIR intermediate complex that yields IO product with low translational energy and in some cases 1,2,6,7 HOI product formed via a five-membered ring transition state. In the case of alkyl and allyl iodides, [1][2][3] the direct scattering appears as enhanced backward scattering of IO product, whereas enhanced sideways scattering is observed 4 for CF 3 I and little 5 direct scattering is observed for CF 3 CH 2 I. This variation in the direction and extent of direct IO scattering has been related 4 to the effect of charge transfer interaction of the form OI + Ron the Renner Teller splitting of the triplet potential energy surface in strongly bent configurations.…”

“…Figure7shows the reaction profile for the triplet3 A′′ potential energy surface for O( 3 P) + CH 2 ICl that is intersected in the entrance valley in bent OIC configurations by the singlet1 A′ potential energy surface that supports a bound OICH 2 Cl intermediate. The ab initio calculations of Marshall17 and Morokuma18 support this picture and predict, a bent geometry with an interbond angle β of 108°and a well depth E 0 of ∼155 kJ mol -1 with respect to reaction products for the singlet OICH 3 intermediate.…”