Control of the photodissociation of CH2BrCl using a few-cycle IR driving laser pulse and a UV control pulse

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Within the $\tilde {\rm B}$B̃ absorption band of CH2BrCl, we theoretically analyze the laser-induced control of the Br/Cl branching ratio, Br + CH2Cl ← CH2BrCl → CH2Br + Cl, with CH2BrCl initially in its vibrational ground state. For weak-field excitation, the Br/Cl branching ratio increases as a function of wavelength, however, for wavelengths below 180 nm the branching ratio cannot be made smaller than 0.4. Using optimal control theory, we show that the branching ratio can be made significantly less than 0.4, only when very strong fields are employed. Thus, the present work strongly suggests that a Tannor-Rice type laser control mechanism for selective bond breakage in CH2BrCl cannot take place without accompanying photoionization.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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A theoretical investigation of the feasibility of Tannor-Rice type control: Application to selective bond breakage in gas-phase dihalomethanes

Shu

Rozgonyi

González

et al. 2012

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“…To cite just a few examples, previous work has included the effect of an external field in dynamics near conical intersection by using a diabatic dipole moment and transition dipole moment dot product with the electric field, [4][5][6] and by using optimal control formalism. 7 In recent work, we have used our Quantum-Ehrenfest (Qu-Eh) 8 method to follow the electron dynamics associated with a pulse that creates a superposition of adiabatic states.…”

Section: Introductionmentioning

confidence: 99%

The quantum-Ehrenfest method with the inclusion of an IR pulse: Application to electron dynamics of the allene radical cation

Tran

Jenkins

Worth

et al. 2020

We describe the implementation of a laser control pulse in the Quantum-Ehrenfest method, a molecular quantum dynamics method that solves the time-dependent Schrödinger equation for both electrons and nuclei. The oscillating electric fielddipole interaction is incorporated directly in the one-electron Hamiltonian of the electronic structure part of the algorithm. We then use the coupled electron-nuclear dynamics of the -system in allene radical cation (•CH2=C=CH2) + as a simple model of a pump-control experiment. We start (pump) with a two-state superposition of two cationic states. The resulting electron dynamics corresponds to the rapid oscillation of the unpaired electron between the two terminal methlylenes. This electron dynamics is in turn coupled to the torsional motion of the terminal methylenes. There is a conical intersection at 90 o twist where the electron dynamics collapses because the adiabatic states become degenerate. After passing the conical intersection the electron dynamics revives. The IR pulse (control) in our simulations is timed to have its maximum at the conical intersection. Our simulations show that the effect of the (control) pulse is to change the electron dynamics at the conical intersection and, as

“…38 Their calculated branching ratios depended strongly on excitation energy. In a later study 39,40 they used the same two-dimensional diabatic model to simulate changing the branching ratio by a combination of IR and UV laser pulses. Our own study presented here will include spin-orbit coupling and will involve dynamics in the full 15 dimensions with N = 24.…”

Section: Introductionmentioning

confidence: 99%

Photochemistry in a dense manifold of electronic states: Photodissociation of CH2ClBr

Valero

Truhlar

2012

We report electronically nonadiabatic dynamics calculations including spin-orbit coupling for the photodissociation of CH(2)ClBr to yield Cl((2)P(3∕2)), Cl((2)P(1∕2)), Br((2)P(3∕2)), and Br((2)P(1∕2)). The potential energy is a 24 × 24 matrix (divided up here into four 6 × 6 blocks in a first approximation to the problem), in a spin-coupled fully diabatic representation obtained by combining the spin-free fourfold way with single-center spin-orbit coupling constants. The spin-free calculations are carried out by multiconfiguration quasidegenerate perturbation theory, and the fully diabatic potentials including spin-orbit coupling are fit to a matrix reactive force field. The dynamics are carried out by the coherent switches with decay of mixing method in the diabatic representation. The results show qualitative agreement with experiment.