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

Abstract

The angular and velocity distributions of the IO product from the reactions O(3P,1D) have been obtained in crossed beam experiments with a rotating mass ] CH 3 I spectrometer detector at collision energies of 55.2 and 64.0 kJ mol~1. The center of mass product angular and translational energy distributions for both the O(3P) and O(1D) reactions have been derived, and the e †ect of electronic excitation and the role of intersystem crossing (ISC) assessed. The O(3P) reaction proceeds, with comparable cross-section, both via a direct mechanism on the triplet potential energy surface with rebound dynamics and via a long-lived complex mechanism following ISC from the triplet to the singlet surface. The O(1D) reaction proceeds on the singlet surface via formation of a complex that lives about one rotational period and also, with comparable cross-section, via direct rebound dynamics following a nearly collinear approach geometry. OÈIÈCH 3 ISC from the triplet to the singlet surface is attributed to the presence of the heavy halogen atom and occurs for bent geometry. These Ðndings are corroborated by recent theoretical calculations on the stationary points of the potential energy surfaces for the system. Calculations based on phase space theory, which assumes conservation of energy and angular momentum and takes into account the various degrees of freedom involved, have been performed ; the product angular and translational energy distributions derived for the O(3P) reaction proceeding via ISC and long-lived collision complex formation are in very good agreement with the experimental quantities.

Reaction dynamics of oxygen atoms with unsaturated hydrocarbons from crossed molecular beam studies: primary products, branching ratios and role of intersystem crossing

“…In general we expect that ISC is efficient when heavy atoms are present, because of the large spin-orbit coupling, as in O( 3 P) + CH 3 I [19]. The extent of ISC along an homologous series of reactions of O( 3 P) with unsaturated hydrocarbons, given our actual state of knowledge, is somewhat unpredictable relying on simple chemical intuition.…”

“…To model combustion systems, however, this kind of information is as relevant as the global rate coefficients, since the products of one elementary reaction are the reactants of a subsequent one in the complex scheme of elementary reactions that account for the global transformation which occurs in combustion environments. In the case of the title reactions, an additional complication is associated to the possible occurrence of intersystem crossing (ISC) from the triplet to the underlying singlet PES, which might open other reaction channels not accessible on the triplet PES [16][17][18][19]. Furthermore, not only they are partial, but they have been obtained mostly at room temperature, that is, far from the actual combustion conditions.…”

A quantum wave-packet study of intersystem crossing effects in the O(P2,1,3,D21)+H2 reaction

“…[15][16][17][18] In this regard, rigorous quantum dynamical calculation has been accomplished only for a few benchmark abstraction reactions of F + H 2 ͑Refs. 4 and 5͒ and Cl+ H 2 , 9 but little has been done for the more complex O͑ 3 P 2,1,0 , 1 D 2 ͒ +H 2 reaction in which the ground surface 1 AЈ favors an insertion mechanism.…”

Adiabatic/Nonadiabatic State-to-State Reactive Scattering Dynamics Implemented on Graphics Processing Units

“…The O( 3 P) + H 2 → H + OH(X 2 Π) reaction is important in understanding the chemistry of combustion processes and other atmospheric reactions. 17 There are intersystem crossings between the triplet and singlet electronic states of the O + H 2 system, 18 and the potential energy surfaces (PESs) of O( 1 D) + H 2 should be included to achieve accurate description of the O( 3 P) + H 2 reaction. Many PESs have been developed to study adiabatic and nonadiabatic reaction dynamics of this reaction.…”