Vibrationally State-Selective Laser Pulse Control of Electronic Branching in OH (X 2Pi/A 2Sigma+) Photoassociation

The quantum dynamics of photoassociative collisions O(3P)+H( 2S) controlled by picosecond laser pulses is explored in the ground (X 2Pi) and excited (A 2Sigma+) electronic states. Coupled Schrödinger equations are solved for representative wavepackets using ab initio data for potentials and (transition) dipole moments. The effect of laser induced electronic transitions as well as the branching between products in the two electronic states is investigated. It is shown that by optimal choice of the laser pulse parameters the ground state process can be achieved with high efficiency (> 80%) and a vibrational state selectivity very close to 100 %. For the excited state, similar results can be obtained by a two-pulse ``dump-pump''strategy. The electronic branching ratio can be controlled by the frequency and the polarization of the laser pulses or the scattering energy of the collision pair

Quantum Molecular Dynamics Driven by Short and Intense Light Pulses: Towards the Limits of the Floquet Picture

Photoinduced quantum molecular dynamics is numerically investigated using two different Schrödinger formulations based on adiabatic ("bare") and Floquet ("dressed") molecular state representations. Computer simulations for the two approaches are compared in terms of numerical accuracy and efficiency where special emphasis is laid on the limit of very short and intense laser pulses. The optical excitation of the HCl+ ion from the X 2Π to the A 2Σ+ state near resonance frequency is investigated as a model system. For a variety of pulse intensities and durations the final population transfer is reproduced accurately by a model based on seven Floquet states only. Elimination of the highly oscillatory terms from the resulting equations allows for the use of much longer time steps in the numerical integration. Even for extremely short pulses with durations down to a single optical cycle, dressed states are still found to be useful. Thus, the Floquet approach provides an efficient tool for the simulation of molecules interacting with short and intense pulses beyond the perturbative regime

Spin-Orbit Induced Association under Ultrafast Laser Pulse Control

The possibility of spin-orbit induced association reactions controlled by optimal femtosecond laser pulses is demonstrated for the example of Br+(3P) + H(2S) → HBr+(X2Π / A2Σ+) association. The nuclear wavepacket dynamics is simulated on the basis of ab initio data for HBr+. To achieve permanent, vibrationally state-selective association, both a Feshbach resonance between collision and vibronic energies and optimal timing between spin-orbit induced and laser pulse assisted transitions are important. The novel method can be effective even when direct photoassociation is forbidden

State-Selective Control For Vibrational Excitation and Dissociation of Diatomic Molecules With Shaped Ultrashort Laser Pulses

Ultrafast state-selective dynamics of diatomic molecules in the electronic ground state under the control of infrared picosecond and femtosecond shaped laser pulses is investigated for the discrete vibrational bound states and for the dissociative continuum states. Quantum dynamics in a classical laser field is simulated for a one-dimensional nonrotating dissociative Morse oscillator, representing the local OH bond in the H2O and HOD molecules. Computer simulations are based on two approaches - exact treatment by the time-dependent Schrödinger equation and approximate treatment by integro-differential equations for the probability amplitudes of the bound states only. Combination of these two approaches is useful to reveal mechanisms underlying selective excitation of the continuum states and above-threshold dissociation in a single electronic state and for designing optimal laser fields to control selective preparation of the high-lying bound states and the continuum states. Optimal laser fields can be designed to yield almost 100% seletive preparation of any prescribed bound state, including those close to the dissociation threshold. State-selective preparation of the highest bound state may be accompanied by the appearance of a quasi-bound molecular state in the continuum with the kinetic energy of the fragments being close to zero. The respective above-threshold dissociation spectrum containes an additional, zero-order peak. The laser-induced dissociation from selectively prepared high-lying bound states is shown to be very efficient, with the dissociation probability approaching the maximal value. Flexible tools of state-selective laser control are developed which enable one to achieve selective control of the dissociation spectra resulting in time-selective and space-selective control of the dissociation fragments

Functionalization of PET track-etched membranes by UV-induced graft (co)polymerization for detection of heavy metal ions in water

Nowadays, water quality monitoring is an essential task since environmental contamination and human exposure to heavy metals increased. Sensors that are able to detect ever lower concentrations of heavy metal ions with greater accuracy and speed are needed to effectively monitor water quality and prevent poisoning. This article shows studies of the modification of flexible track-etched membranes as the basis for the sensor with various polymers and their influence on the accuracy of detection of copper, cadmium, and lead ions in water. We report the UV-induced graft (co)polymerization of acrylic acid (AA) and 4-vinylpyridine (4-VPy) on poly(ethylene terephthalate) track-etched membrane (PET TeMs) and use them after platinum layer sputtering in square wave anodic stripping voltammetry (SW-ASV) for detection of Cu2+, Cd2+, and Pb2+. Optimal conditions leading to functionalization of the surface and retention of the pore structure were found. Modified membranes were characterized by SEM, FTIR, X-ray photoelectron spectroscopy (XPS) and colorimetric analysis. The dependence of the modification method on the sensitivity of the sensor was shown. Membrane modified with polyacrylic acid (PET TeMs-g-PAA), poly(4-vinylpyridine) (PET TeMs-g-P4VPy), and their copolymer (PET TeMs-g-P4VPy/PAA) with average grafting yield of 3% have been found to be sensitive to μg/L concentration of copper, lead, and cadmium ions. Limits of detection (LOD) for sensors based on PET TeMs-g-PAA are 2.22, 1.05, and 2.53 μg/L for Cu2+, Pb2+, and Cd2+, respectively. LODs for sensors based on PET TeMs-g-P4VPy are 5.23 μg/L (Cu2+), 1.78 μg/L (Pb2+), and 3.64 μg/L (Cd2+) μg/L. PET TeMs-g-P4VPy/PAA electrodes are found to be sensitive with LODs of 0.74 μg/L(Cu2+), 1.13 μg/L (Pb2+), and 2.07 μg/L(Cd2+). Thus, it was shown that the modification of membranes by copolymers with carboxylic and amino groups leads to more accurate detection of heavy metal ions, associated with the formation of more stable complexes. © 2019 by the authors.Ministry of Education and Science of the Republic of KazakhstanMinistry of Education and Science of the Republic of KazakhstanFunding: The research was funded by the Ministry of Energy of the Republic of Kazakhstan (technological program, #74 on 02.04.2018).Acknowledgments: The research was funded by the Ministry of Energy of the Republic of Kazakhstan (technological program, #74 on 02.04.2018)

Infrared Picosecond Laser Control of Acceleration of Neutral Atoms: Model Simulations for the Collision Pair O + H

The quantum dynamics of an atomic collision pair interacting with the electric field of an infrared sub-picosecond laser pulse is investigated by means of propagation of representative wavepackets. Depending on the optimal choice of the laser pulse, two competing types of scattering events are encountered. First, for continuum → bound transitions, effective (85 %) vibrationally state-selective photoassociation reactions O + H → OH(ν) are induced by stimulated emission [Chem. Phys. Lett. 260 (1996) 604]. Second, for non-resonant cases, laser controlled acceleration of the colliding atoms can be achieved. Laser field optimization allows to design the energy distribution of the scattered atoms

A Reflection Principle for the Control of Molecular Photodissociation in Solids: Model Simulation for F2 in Ar

Laser pulse induced photodissociation of molecules in rare gas solids is investigated by representative quantum wavepackets or classical trajectories which are directed towards, or away from cage exits, yielding dominant photodissociation into different neighbouring cages. The directionality is determined by a sequence of reflections inside the relief provided by the slopes of the potential energy surface of the excited system, which in turn depend on the initial preparation of the matrix isolated system, e.g. by laser pulses with different frequencies or by vibrational pre-excitation of the cage atoms. This reflection principle is demonstrated for a simple, two-dimensional model of F2 in Ar