Nonstationary Electronic States and Site-Selective Reactivity

Faraday discussions, 2014

Gas-phase scattering analysis, data analysis Addendum The referenced proposal builds on our past studies, L560, to explore the imaging of chemical dynamics with ultrafast time resolution and atomic scale molecular structure resolution. It makes the case that it will be possible to create a molecular movie that reveals just how the molecular structure changes, in real time, as the molecule undergoes a chemical reaction.

Journal of Mathematical Chemistry, 2005

The method discussed in this work provides a theoretical framework where simple chemical reactions resemble any other standard quantum process, i.e., a transition in quantum state mediated by the electromagnetic field. In our approach, quantum states are represented as a superposition of electronic diabatic basis functions, whose amplitudes can be modulated by the field and by the external control of nuclear configurations. Using a one-dimensional three-state model system, we show how chemical structure and dynamics can be represented in terms of these control parameters, and propose an algorithm to compute the reaction probabilities. Our analysis of effective energy barriers generalizes previous ideas on structural similarity between reactant, and product, and transition states using the geometry of conventional reaction paths. In the present context, exceptions to empirical rules such as the Hammond postulate appear as effects induced by the environment that supplies the external field acting on the quantum system.

Chemical Science, 2010

A variety of chemical phenomena are governed by non-adiabatic transitions at conical intersections of potential energy surfaces, if not directly, but indirectly in the midst of the processes. In other words, the non-adiabatic transition makes one of the most significant key mechanisms in chemical dynamics. Since the basic analytical theory is now available to treat the transitions, it is possible to comprehend the dynamics of realistic chemical and biological systems with the effects of transitions taken into account properly. Another important quantum mechanical effect of tunneling can also be taken into account. Furthermore, it becomes feasible to control chemical dynamics by controlling the non-adiabatic transitions at conical intersections, and also to develop new molecular functions by using peculiar properties of non-adiabatic transitions. These may be realized, if we apply appropriately designed laser fields. This perspective review article explains the above mentioned ideas based on the authors' recent activities. The non-adiabatic chemical dynamics is expected to open a new dimension of chemistry.

Annual review of physical chemistry, 1998

To predict the branching between energetically allowed product channels, chemists often rely on statistical transition state theories or exact quantum scattering calculations on a single adiabatic potential energy surface. The potential energy surface gives the energetic barriers to each chemical reaction and allows prediction of the reaction rates. Yet, chemical reactions evolve on a single potential energy surface only if, in simple terms, the electronic wavefunction can evolve from the reactant electronic configuration to the product electronic configuration on a time scale that is fast compared to the nuclear dynamics through the transition state. The experiments reviewed here investigate how the breakdown of the Born-Oppenheimer approximation at a barrier along an adiabatic reaction coordinate can alter the dynamics of and the expected branching between molecular dissociation pathways. The work reviewed focuses on three questions that have come to the forefront with recent theory and experiments: Which classes of chemical reactions evidence dramatic nonadiabatic behavior that influences the branching between energetically allowed reaction pathways? How do the intramolecular distance and orientation between the electronic orbitals involved influence the nonadiabaticity in the reaction? How can the detailed nuclear dynamics mediate the effective nonadiabatic coupling encountered in a chemical reaction?

Chemical Reviews, 2006

Damien Riedel received his B.Sc. in physics from the University of Besanc ¸on. His M.Sc. work in optics and electronics was on speckle interferometry using a scanning near-field optical microscope in the Laboratoire d'Optique P. M. Duffieux. He obtained his Ph.D. in physics in 1998 under the supervision of Prof. M. C. Castex from the University of Paris XIII, where his postgraduate work in laser physics and surface science concerned the vacuum ultraviolet laser interaction with polymer surfaces and fluorescence spectroscopy. He then joined the group of Prof. R. E. Palmer in Birmingham, U.K., on a postdoctoral Marie-Curie Fellowship. In the Nanoscale Physics Laboratory, he worked on an ultrashort-pulse laser created by high-order harmonic generation in rare gases. He developed applications on surface photodesorption experiments and room temperature STM combined with a laser. In 2001, he joined the CNRS to work with Dr. Ge ´rald Dujardin, and his research deals with molecular electronics and molecular manipulation via highly localized electronic excitation with a low-temperature STM on semiconductors. He is developing projects that combine a laser and an STM and involve collection of fluorescence on the low-temperature STM.

Advanced Series in Physical Chemistry, 2011

Biophysical Journal, 2014

When structures that interconvert on a given time scale are lumped together, the corresponding free-energy surface becomes af u n c t i o no ft h eo b s e r v a t i o nt i m e .T h i sv i e wi se q u i v a l e n tt o grouping structures that are connected by free-energy barriers below a certain threshold. We illustrate this time dependence for some benchmark systems, namely atomic clusters and alanine dipeptide, highlighting the connections to broken ergodicity, local equilibrium, and "feasible" symmetry operations of the molecular Hamiltonian.

The Journal of Physical Chemistry, 1993

The electronic superexchange interactions, which enable long-range electron transfer in complex molecular structures, such as proteins, are beyond the capacity of standard electronic structure methods due to their size, inhomogeneity, aperiodicity, and sensitivity to the many weak interactions between the nominally insulating atoms of the intervening medium. The inhomogeneous aperiodic lattice theory, presented here, is a novel strategy implemented as a quantum molecular model, designed to enable the calculation of electronic transfer matrix elements in large macromolecular systems by redesigning the electronic structure problem into a twotiered approach. The procedure is (i) assembly of the diagonal and off-diagonal elements of the Hamiltonian matrix by comparison, respectively, with experimental ionization potentials for individual amino acids and with triple-cab initio studies of resonance integrals and then (ii) nonperturbative computation of the macromolecular electronic coupling from this inhomogeneous aperiodic lattice (IAL) Hamiltonian. The IAL method includes all the occupied orbitals of the entire protein in a full-matrix calculation with no a priori assumption about pathways or spatial subregions important in spanning the distance between the redox sites. The nonperturbative approach and overall strategy of subunit-level calibration, distinct from standard semiempirical atom-level calibration, are first presented. A specific algorithm for Hamiltonian construction and tests against a series of medium sized molecules then follow. This nonperturbative matrix inversion strategy is computationally efficient and can treat a system the size of cytochrome c in less than a minute. Most important to the mechanistic study of redox proteins, the absolute results in cm-l for the computed charge resonance energies of three ruthenium modified cytochrome c derivatives compare well with experiment. k,, = (2a/h)lA12(FCWD) Thus the rate constant k, depends upon the product of two factors, lA)* and FCWD, arising, respectively, from the participation of the electronic and nuclear motions in the kinetic process. The Franck-Condon weighted density of final vibronic states, FCWD, is the quantum analogue of the activation factor in the original Marcus rate expression, which describes and predicts the dependence of the rate upon the reorganization free energy and reaction e~ergonicity.1~ This factor is treated quantum mechanically, semiclassically, or in the classical limit as appropriate to the degree of vibrational excitationl"18 and need not be considered

Chemical Physics, 2016

The simulation of nonadiabatic dynamics in extended molecular systems involving hundreds of atoms and large densities of states is particularly challenging. Nonadiabatic coupling terms (NACTs) represent a significant numerical bottleneck in surface hopping approaches. Rather than using unreliable NACT cutting schemes, here we develop "on-the-fly" state limiting methods to eliminate states that are no longer essential for the non-radiative relaxation dynamics as a trajectory proceeds. We propose a state number criteria and an energy-based state limit. The latter is more physically relevant by requiring a user-imposed energy threshold. For this purpose, we introduce a local kinetic energy gauge by summing contributions from atoms within the spatial localization of the electronic wavefunction to define the energy available for upward hops. The proposed state limiting schemes are implemented within the nonadiabatic excited-state molecular dynamics framework to simulate photoinduced relaxation in poly-phenylene vinylene (PPV) and branched poly-phenylene ethynylene (PPE) oligomers for benchmark evaluation.