[Show abstract][Hide abstract] ABSTRACT: We suggest optical modulation of the dielectric function of a molecular monolayer adsorbed on a metal surface as a potential means of controlling plasmon resonance phenomena. The dielectric function is altered using a laser pulse of moderate intensity and linear polarization to align the constituent molecules. After the pulse, the monolayer returns to its initial state. Time-dependent, optically controlled dielectric function is illustrated by molecular dynamics calculations.Keywords: surface plasmon resonance; self-assembled monolayer; molecular dynamics; molecular alignment; polarizability
[Show abstract][Hide abstract] ABSTRACT: Shaped ultrafast laser pulses were used to study and control the ionization
dynamics of electronically excited pyrazine in a pump and probe experiment. For
pump pulses created without feedback from the product signal, the ion growth
curve (the parent ion signal as a function of pump/probe delay) was described
quantitatively by the classical rate equations for internal conversion of the
$S_2$ and $S_1$ states. Very different, non-classical behavior was observed
when a genetic algorithm (GA) was used to minimize the ion signal at some
pre-determined target time, T. Two qualitatively different control mechanisms
were identified for early (T$<1.5$ ps) and late (T$>1.5$ ps) target times. In
the former case, the ion signal was largely suppressed for $t<T$, while for $t
\gg T$ the ion signal produced by the GA-optimized pulse and a transform
limited (TL) pulse coalesced. In contrast, for $T>1.5$ ps the ion growth curve
followed the classical rate equations for $t<T$, while for $t \gg T$ the
quantum yield for the GA-optimized pulse was much smaller than for a TL pulse.
We interpret the first type of behavior as an indication that the wave packet
produced by the pump laser is localized in a region of the $S_2$ potential
energy surface where the vertical ionization energy exceeds the probe photon
energy, whereas the second type of behavior may be described by a reduced
absorption cross section for $S_0 \rightarrow S_2$ followed by incoherent decay
of the excited molecules.
[Show abstract][Hide abstract] ABSTRACT: We suggest the combination of single molecule pulling and optical control as a way to enhance control over the electron transport characteristics of a molecular junction. We demonstrate using a model junction consisting of biphenyl-dithiol coupled to gold contacts. The junction is pulled while optically manipulating the dihedral angle between the two rings. Quantum dynamics simulations show that molecular pulling enhances the degree of control over the dihedral angle and hence over the transport properties.
[Show abstract][Hide abstract] ABSTRACT: Although the vast majority of studies of transport via molecular-scale heterojunctions have been conducted in the (static) energy domain, experiments are currently beginning to apply time domain approaches to the nanoscale transport problem, combining spatial with temporal resolution. It is thus an opportune time for theory to develop models to explore both new phenomena in, and new potential applications of, time-domain, coherently driven molecular electronics. In this work, we study the interaction of a molecular phonon with an electronic wavepacket transmitted via a conductance junction within a time-domain model that treats the electron and phonon on equal footing and spans the weak to strong electron-phonon coupling strengths. We explore interference between two coherent energy pathways in the electronic subspace, thus complementing previous studies of coherent phenomena in conduction junctions, where the stationary framework was used to study interference between spatial pathways. Our model provides new insights into phase decoherence and population relaxation within the electronic subspace, which have been conventionally treated by density matrix approaches that often rely on phenomenological parameters. Although the specific case of a transport junction is explored, our results are general, applying also to other instances of coupled electron-phonon systems.
The Journal of Chemical Physics 07/2014; 141(4):044103. · 3.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We explore the interaction between a quantum emitter and a metal nanoring by numerical solution of coupled Maxwell-Liouville equations. When the quantum emitter and nanoring are subjected to an incident plane wave, coupling between the quantum emitter and a dark plasmon supported by the nanoring gives rise to a similar lineshape to the familiar Fano type. It results from the excitation of a dark plasmon via intermediary participation of the quantum emitter. The dark plasmon is characterized through the width and shift parameters of the emitter peak in the absorption spectrum of the nanoparticle. Our results are obtained with the help of finite-difference time-domain method and a recently proposed symmetry-adapted averaging approach.
The Journal of Chemical Physics 06/2014; 140(23):234311. · 3.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We propose the general methodology to design the Wigner representations with
the desired dynamical and semiclassical properties in the phase spaces with
nontrivial topology. As an illustration, two representations of molecular
rotations are developed to suit the computational demands of contemporary
applications of laser alignment, diagnostics of reaction dynamics, studies of
scattering and dissipative processes.
[Show abstract][Hide abstract] ABSTRACT: We present an approach to accurately construct the few-state model Hamiltonians for singlet fission processes on the basis of an ab initio electronic structure method tailored to dimer wave functions, called an active space decomposition strategy. In this method, the electronic structure of molecular dimers is expressed in terms of a linear combination of products of monomer states. We apply this method to tetracene and pentacene, using monomer wave functions computed by the restricted active space (RAS) method. Near-exact wave functions are computed for π-electrons of dimers that contain up to 7 × 1012 electronic configurations. Our product ansatz preserves the diabatic picture of the minimal dimer model, allowing us to accurately identify model Hamiltonians. The wave functions obtained from the model Hamiltonians account for more than 99% of the total wave functions. The resulting model Hamiltonians are shown to be converged with respect to all the parameters in the model, and corroborate previously reported coupling strengths.
The Journal of Physical Chemistry C 06/2014; 118(24):12700–12705. · 4.84 Impact Factor