Direct evidence for nonadiabatic dynamics in atom+polyatom reactions: Crossed-jet laser studies of F+D2O→DF+OD

Abstract

Quantum-state-resolved reactive-scattering dynamics of F+D(2)O-->DF+OD have been studied at E(c.m.)=5(1) kcal/mol in low-density crossed supersonic jets, exploiting pulsed discharge sources of F atom and laser-induced fluorescence to detect the nascent OD product under single-collision conditions. The product OD is formed exclusively in the v(OD)=0 state with only modest rotational excitation (<E(rot)> =0.50(1) kcal/mol), consistent with the relatively weak coupling of the 18.1(1) kcal/mol reaction exothermicity into "spectator" bond degrees of freedom. The majority of OD products [68(1)%] are found in the ground ((2)Pi(32) (+/-)) spin-orbit state, which adiabatically correlates with reaction over the lowest and only energetically accessible barrier (DeltaE( not equal) approximately 4 kcal/mol). However, 32(1)% of molecules are produced in the excited spin-orbit state ((2)Pi(12) (+/-)), although from a purely adiabatic perspective, this requires passage over a DeltaE( not equal) approximately 25 kcal/mol barrier energetically inaccessible at these collision energies. This provides unambiguous evidence for nonadiabatic surface hopping in F+D(2)O atom abstraction reactions, indicating that reactive-scattering dynamics even in simple atom+polyatom systems is not always isolated on the ground electronic surface. Additionally, the nascent OD rotational states are well fitted by a two-temperature Boltzmann distribution, suggesting correlated branching of the reaction products into the DF(v=2,3) vibrational manifold.

Final state-resolved mode specificity in HX + OH → X + H2O (X = F and Cl) reactions: A quasi-classical trajectory study

“…[32][33][34][35][36][37][38] The kinetics of (R1) in the reverse direction has also been studied by many groups. [39][40][41] For (R1), there has been no experimental study of its dynamics in the forward direction, although the reverse reaction has been the subject of several investigations, [42][43][44][45][46][47] which found highly vibrationally excited HF and internally cold OH products. On the other hand, there is only one experimental dynamical study on R2, which measured the vibrational excitation of the water product 48 at 298 K. Experimental work has also been reported for the reverse Cl + HOD reaction, focusing on bond-selective chemistry.…”

State-to-state quantum dynamics of the F + HCl (vi = 0, ji = 0) → HF(vf, jf) + Cl reaction on the ground state potential energy surface

“…6 Adding to the complexity, the spin-orbit splitting of the fluorine atom leads to important nonadiabatic dynamics in the entrance channel. [7][8][9][10] More recently, surprising features were seen in the F + H 2 O reaction, including a covalently bonded pre-reaction complex, 11 stereodynamically facilitated enhancement of reactivity 12 and unusual vibrational mode selectivity. 13 In this work, we focus on the F + HCl -HF + Cl reaction (DH 0 B À33 kcal mol À1 ), which is a prototype for asymmetric hydrogen abstraction.…”

Communication: Covalent nature of X⋯H2O (X = F, Cl, and Br) interactions

“…6 In this Communication, we focus on the pre-reaction complexes for gas-phase reactions between open-shell halogen atoms and H 2 O. These reactions are important in atmospheric and interstellar chemistry, and have attracted much recent experimental [7][8][9][10][11][12] and theoretical attention. 6,[13][14][15][16][17] Due to the free-radical nature of halogen atoms, their interactions with other molecules are far more complex than the common van der Waals interactions between closed-shell molecules.…”