Dynamical Resonances in F H2 Reactions

S.L. Latham, J.F. McNutt, R.E. Wyatt, M.J. Redmon, Quantum dynamics of the F+H2 reaction Resonance models, and energy and flux distributions in the transition state, J. Chem. Phys. 69 (1978) 3746. 

However, it is unlikely that the SSDW method using the simple distortion potentials discussed in Section 2.2. can accurately describe the dynamics of the F+H2 reaction on the Muckerman 5 surface. Approximate 3D quantum calculations for F+Hp indicate that the resonances obtained in exact collinear quantum reaction probabilities are not completely averaged out on going to 30. As emphasized in Section... 

V. Aquilanti, S. Cavalli, D. De Fazio, A. Simoni, and T.V. Tscherbul, Direct evaluation of the lifetime matrix by the hyperquantization algorithm Narrow resonances in the F + H2 reaction dynamics and their splitting for nonzero angular momentum. J. Chem. Phys., 123(054314) 1-15, 2005. 

In light of previous experimental and theoretical work on the F f H2 reaction, it can be seen why an experisient of this complexity is necessary in order to observe dynamic resonances in this reaction. The energetics for this reaction and its isotopic variants are displayed in Figure 1. Chemical laser (11) and infrared chemiluminescence (12) studies have shown that the HF product vibrational distribution is hi ly inverted, with most of the population in v=2 and v°°3. A previous crossed molecular beam study of the F + D2 reaction showed predominantly back-scattered DF product (13). These observations were combined with the temperature dependence of the rate constants from an early kinetics experiment (14) in the derivation of the semiempirical Muckerman 5 (M5) potential energy surface (15) using classical trajectory methods. Although an ab initio surface has been calculated (16), H5 has been the most widely used surface for the F H2 reaction over the last several years. 

The hydrogen transfer reactions Cl + HC1, I + HI, and I + DI present a more difficult test of quantized transition state control of chemical reactivity. In contrast to the H + H2, D + H2, O + H2, and F + H2 reactions, the quantized transition state structure in the accurate dynamics of these reactions is almost completely obscured by features that have been attributed to trapped-state resonances and rotational thresholds (17-19). Al-... 

The F + H2 — HF + FI reaction is one of the most studied chemical reactions in science, and interest in this reaction dates back to the discovery of the chemical laser.79 In the early 1970s, a collinear quantum scattering treatment of the reaction predicted the existence of isolated resonances.80 Subsequent theoretical investigations, using various dynamical approximations on several different potential energy surfaces (PESs), essentially all confirmed this prediction. The term resonance in this context refers to a transient metastable species produced as the reaction occurs. Transient intermediates are well known in many kinds of atomic and molecular processes, as well as in nuclear and particle physics.81 What makes reactive resonances unique is that they are not necessarily associated with trapping... 

Using the H-atom Rydberg tagging time-of-flight crossed molecular beam technique, Dr. Ren studied the reaction resonance and non-adiabatic effects at a full quantum resolved level in the F + H2 system. Through state-to-state resolved experiments, he provided the first conclusive evidence of reaction resonances in the F %,2) + H2 -> HF + H reaction. The dramatic difference between the dynamics for the F( P3/2) + H2(j = 0,1) reactions represents a textbook example of the role of reactant rotational level in resonance phenomena in this benchmark system. Dr. Ren has also carried out a very high-resolution experimental study on the dynamics of the isotope substituted reaction, F( P3/2) -I- HD -> HF -I- D, with spectroscopic accuracy (a few cm ). These findings provided a very clear physical picture for reaction resonances in this benchmark system, which has eluded us for more than 30 years. 

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