Role of Intersystem Crossing in the Dynamics of the O(³P) + (CH₃)₂CHI, (CH₃)₃CI Reactions

Abstract

Reactive scattering of O( 3 P) atoms with (CH 3 ) 2 CHI and (CH 3 ) 3 CI molecules has been studied at an initial translational energy E ∼ 51 kJ mol -1 using a supersonic beam of O atoms seeded in He buffer gas from a microwave discharge source. Sharply backward peaked angular distributions of IO product scattering are observed with distinctly higher product translational energy for the backward compared with the forward and sideways scattering. Mildly forward and backward peaked angular distributions slightly favoring the backward direction are observed for HOI product scattering with the product translational energy distribution being independent of scattering angle. The component of IO scattering with low product translational energy and the HOI scattering are both attributed to intersystem crossing from the lowest triplet 3 A′′ potential energy surface to a bound OIR intermediate on the singlet 1 A′ potential energy surface. The HOI product is formed via a five-membered ring transition state where the H atom is abstracted from a terminal CH 3 group of the alkyl radical R. The fraction of singlet OIR complexes which dissociates to HOI product compared with IO product increases from ∼0.3 for R ) C 2 H 5 to ∼0.5 for R ) (CH 3 ) 2 CH and (CH 3 ) 3 C. The backward scattered IO product is attributed to direct reaction over the triplet 3 A′′ potential energy surface and contributes a fraction ∼ 1 / 5 to the total reaction cross section largely independent of the alkyl radical.Dynamics of the O( 3 P) + (CH 3 ) 2 CHI, (CH 3 ) 3 CI Reactions

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

“…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. In the case of alkyl and allyl iodides, − 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 + R - on the Renner Teller splitting of the triplet potential energy surface in strongly bent configurations.…”

“…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. In the case of alkyl and allyl iodides, − 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.…”

Probing the cyclic transition state in the reaction O(3P)+alkyl iodides to form HOI: electronic, steric and thermodynamic factors influencing the reaction pathway

“…16 This enhancement in the reaction rate constant arises due to an initial intersystem crossing to the singlet intermediate complex, an intermediate which can be formed only in the reactions with the alkyl iodides and not with the other halogenated alkyl precursors, followed by a recrossing to the triplet surface IO product. 10,11,13,17 This has been shown to be the minimum energy path for this reaction.…”

Dynamics of Ring Cleavage and Substitution in the Reactive Scattering of O(3P) Atoms with C2H4S and C4H4S Molecules

“…The apparatus was the same as that previously employed in studies , of O( 3 P) atoms with alkyl iodide molecules. A supersonic beam of O atoms seeded in He buffer gas was produced from a high-pressure microwave discharge source …”