Response of solid Ne upon photoexcitation of a NO impurity: a quantum dynamics study

The ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation is studied using a quantum dynamical approach based on a multi-dimensional shell model, with the shell radii being the dynamical variables. The Ne-NO interaction being only weakly anisotropic allows the model to account for the main dynamical features of the rare gas solid. Employing quantum wave packet propagation within the time dependent Hartree approximation, both, the static deformation of the solid due to the impurity and the dynamical response after femtosecond excitation, are analysed. The photoinduced dynamics of the surrounding rare gas atoms is found to be a complex high-dimensional process. The approach allows to consider realistic time-dependent femtosecond pulses and the effect of the pulse duration is clearly shown. Finally, using the pulse parameters of previous experiments, pump-probe signals are calculated and found to be in good agreement with experimental results, allowing for a clear analysis of the ultrafast mechanism of the energy transfer into the solid.     

Accuracy of gates in a quantum computer based on vibrational eigenstates

A model is developed to study the properties of a quantum computer that uses vibrational eigenstates of molecules to implement the quantum information bits and shaped laser pulses to apply the quantum logic gates. Particular emphasis of this study is on understanding how the different factors, such as properties of the molecule and of the pulse, can be used to affect the accuracy of quantum gates in such a system. Optimal control theory and numerical time-propagation of vibrational wave packets are employed to obtain the shaped pulses for the gates NOT and Hadamard transform. The effects of the anharmonicity parameter of the molecule, the target time of the pulse and of the penalty function are investigated. Influence of all these parameters on the accuracy of qubit transformations is observed and explained. It is shown that when all these parameters are carefully chosen the accuracy of quantum gates reaches 99.9%.     

Vibrationally state-selective photoassociation by infrared sub-picosecond laserr pulses: model simulations for O + H → OH(ν)

The quantum dynamics of a photoassociation reaction in the electronic ground state controlled by an infrared picosecond laser pulse is investigated. The association reaction O + H → OH(ν) is simulated by representative wavepackets. The OH molecule to be formed is modeled as a non-rotating Morse oscillator. It is shown that the initial free continuum state of O + H can be transferred selectively into a specified vibrational bound state by interaction with an infrared laser pulse. Optimal design of the laser control field leads to high association probability with very high vibrational state selectivity.     

Capillary electrophoretic determination of carboxyhemoglobin concentrations in postmortem blood samples

The use of capillary electrophoresis (CE) as an alternative to existing methods of quantitation of carbon monoxide (CO) in hemoglobin from postmortem blood samples is presented. The isolation of heme (the portion of the hemoglobin molecule in which CO binding takes place) from hemoglobin is described. Reduced (containing no gas molecules) heme and CO-heme isolated from hemoglobin standards were successfully separated using CE. Heme and CO-heme were also isolated from blood samples of accident victims and analyzed using CE. A quantifiable difference in the CO-heme signals from blood samples containing fatal and nonfatal levels of CO was observed.     

Resonance Raman and infrared spectroscopic studies of high-output forms of human soluble guanylyl cyclase

The allosteric regulator BAY-41-2272 converts the CO adduct of soluble guanylyl cyclase (CO-sGC) enzyme from a low- to high-output form, with respect to production of cGMP. Resonance Raman (RR) and Fourier Transform Infrared (FTIR) spectroscopic techniques are used to show that the CO-sGC exists as major and minor conformers, both having nu(Fe-CO) and nu(C-O) modes characteristic of 6-coordinate species. It is further shown that addition of BAY-41-2272 to the CO adduct induces the transition of some fraction of the initial CO-heme adducts into two new CO-heme complexes, the fractional conversion being dependent on the temperature. One new complex displays vibrational modes characteristic of pentacoordinated CO-adduct, and its formation is not affected by temperature. The second complex, although slightly different from the original CO-adducts, is hexacoordinated, and its formation is facilitated by temperature. The production of substantial amounts of the 5-coordinate CO adduct upon addition of BAY-41-2272, reveals the fact that several out-of-plane heme deformation modes are simultaneously activated, an observation similar to that realized upon NO activation. While the precise nature of these modes will require elucidation by isotopic labeling experiments, by analogy with earlier studies of other heme proteins, several bands associated with modes attributable to peripheral substituent deformations and methine carbon movements are implicated. The documented formation of two new forms upon addition of Bay-41-2272 (a 5-coordinate and a new 6-coordinate form) is discussed with respect to the implications for enzyme activation.     

Femtosecond quantum control of molecular dynamics in the condensed phase

We review the progress in controlling quantum dynamical processes in the condensed phase with femtosecond laser pulses. Due to its high particle density the condensed phase has both high relevance and appeal for chemical synthesis. Thus, in recent years different methods have been developed to manipulate the dynamics of condensed-phase systems by changing one or multiple laser pulse parameters. Single-parameter control is often achieved by variation of the excitation pulse's wavelength, its linear chirp or its temporal subpulse separation in case of pulse sequences. Multiparameter control schemes are more flexible and provide a much larger parameter space for an optimal solution. This is realized in adaptive femtosecond quantum control, in which the optimal solution is iteratively obtained through the combination of an experimental feedback signal and an automated learning algorithm. Several experiments are presented that illustrate the different control concepts and highlight their broad applicability. These fascinating achievements show the continuous progress on the way towards the control of complex quantum reactions in the condensed phase.     

A hybrid local/global optimal control algorithm for dissipative systems with time-dependent targets: formulation and application to relaxing adsorbates

Open-system quantum optimal control theory for optical control of the dynamics of a quantum system in contact with a dissipative bath is used here for explicitly time-dependent target operators, O(t). Global and local control strategies are combined in a novel algorithm by defining a set of time slices, into which the total control time is subdivided. The optimization then proceeds locally forward in time from subinterval to subinterval, while within each subinterval global control theory is used with iterative forward-backward propagation. The subintervals are connected by appropriate boundary conditions. In the present paper, all operators are represented in the basis of the eigenstates of the field-free system Hamiltonian. The algorithm is first applied to and its computational performance tested for a two-level system with energy and phase relaxation, and later extended to a many-level model. Model parameters are chosen to represent the IR pulse excitation of the adsorbate-surface stretch mode of vibrationally relaxing CO on a Cu(100) surface. Various time-dependent targets are formulated to achieve (i) population inversion, (ii) the creation of a wavepacket, and (iii) overtone excitation by "ladder climbing."     

How CO binds to hexacoordinated heme in neuroglobin protein

In the present work, density functional theory (DFT) has been used to investigate CO binding to the hexacoordinated heme in neuroglobin (Ngb) protein. Structural relaxation of the selected model system in the protein environment has been fully included by the alternative quantum and molecular mechanical optimizations. The polarized continuum model (PCM) was used to simulate interaction between the model system and the protein environment. The CO binding could take place in a concerted way and a barrier of 17.9 kcal mol(-1) was predicted on the concerted singlet pathway, which is not favorable in energy. The adiabatically sequential pathway requires an energy of 14.5 kcal mol(-1) for formation of the singlet intermediate. There exist two nonadiabatic sequential pathways for the CO binding, which involves the triplet and quintet states of intermediate. Both the singlet/triplet and singlet/quintet intersections play an important role in nonadiabatic sequential processes, which enhance the probability that the processes occur. The nonadiabatic processes that involve the triplet and quintet states of intermediate are the most probable pathways for the CO binding to the hexacoordinated heme in Ngb to form the product complex.     

Quantum dynamics of solid Ne upon photo-excitation of a NO impurity: A Gaussian wave packet approach

A high-dimensional quantum wave packet approach based on Gaussian wave packets in Cartesian coordinates is presented. In this method, the high-dimensional wave packet is expressed as a product of time-dependent complex Gaussian functions, which describe the motion of individual atoms. It is applied to the ultrafast geometrical rearrangement dynamics of NO doped cryogenic Ne matrices after femtosecond laser pulse excitation. The static deformation of the solid due to the impurity as well as the dynamical response after femtosecond excitation are analyzed and compared to reduced dimensionality studies. The advantages and limitations of this method are analyzed in the perspective of future applications to other quantum solids.     

New mechanistic insight into electronically excited CO-NiO(100): a quantum dynamical analysis

In a recent study Redlich et al. [Redlich et al., Chem. Phys. Lett. 2006, 420, 110] measured the velocity distribution of CO molecules desorbing from a NiO(100) surface after irradiation with an ultraviolet (UV) laser pulse. Due to the complexity of the involved processes no experimental evidence on the excitation and desorption mechanism could be obtained. In recent ab initio studies Mehdaoui et al. [Mehdaoui et al., Phys. Rev. Lett. 2007, 98, 037601] have shown that a 5sigma --> 2pi* (a (3)Pi) like transition within the CO adsorbate is most likely the crucial excitation step in the CO-NiO(100) system. At first sight this seems unlikely, since the interaction of CO molecules with the NiO(100) surface is very weak (-0.30 eV) and the corresponding CO gas phase transition energy is about 1.5 eV higher than the laser pulse energy of 4.66 eV used in the experiment. In this work we give further insight into relevant electronically excited states and identify the desorption mechanism by analysing the dynamical processes after laser excitation by quantum dynamical wave packet simulations on the basis of three-dimensional (3D) ab initio potential energy surfaces. The results corroborate the so far discussed excitation mechanism, which proposes the formation of a genuine C-Ni bond as the driving force for photodesorption, as the crucial excitation step.     

Ab initio design of picosecond infrared laser pulses for controlling vibrational-rotational excitation of CO molecules

Optimal control of rovibrational excitations of the CO molecule using picosecond infrared laser pulses is described in the framework of the electric-nuclear Born-Oppenheimer approximation [G. G. Balint-Kurti et al., J. Chem. Phys. 122, 084110 (2005)]. The potential energy surface of the CO molecule in the presence of an electric field is calculated using coupled cluster theory with a large orbital basis set. The quantum dynamics of the process is treated using a full three dimensional treatment of the molecule in the laser field. The detailed mechanisms leading to efficient control of the selected excitation processes are discussed.     

The influence of ultrafast laser pulses on electron transfer in molecular wires studied by a non-Markovian density-matrix approach

New features of molecular wires can be observed when they are irradiated by laser fields. These effects can be achieved by periodically oscillating fields but also by short laser pulses. The theoretical foundation used for these investigations is a density-matrix formalism where the full system is partitioned into a relevant part and a thermal fermionic bath. The derivation of a quantum master equation, either based on a time-convolutionless or time-convolution projection-operator approach, incorporates the interaction with time-dependent laser fields nonperturbatively and is valid at low temperatures for weak system-bath coupling. From the population dynamics the electrical current through the molecular wire is determined. This theory including further extensions is used for the determination of electron transport through molecular wires. As examples, we show computations of coherent destruction of tunneling in asymmetric periodically driven quantum systems, alternating currents and the suppression of the directed current by using a short laser pulse.     

Pressure dependence for the CO quantum yield in the photolysis of acetone at 248 nm: a combined experimental and theoretical study

The quantum yield of CO in the laser pulse photolysis of acetone at 248 nm and at 298 K in the pressure range 20-900 mbar (N2) has been measured directly using quantitative infrared diode laser absorption of CO. It is found that the quantum yield of CO shows a significant dependence on total pressure with Phi(CO) decreasing with pressure from around 0.45 at 20 mbar to approximately 0.25 at 900 mbar. From a combination of ab initio quantum chemical calculations on the molecular properties of the acetyl (CH3CO) radical and its unimolecular fragmentation as well as the application of statistical (RRKM) and dynamical calculations we show that CO production results from prompt secondary fragmentation (via(2a)) of the internally excited primary CH3CO* photolysis product with an excess energy of approximately 62.8 kJ mol(-1). Hence, our findings are consistent with a consecutive photochemically induced decomposition model, viz. step (1): CH3COCH3+hv--> CH3CO*+ CH3, step (2a): CH3CO*--> CH3+ CO or step (2b) CH3CO*-(+M)--> CH3CO. Formation of CO via a direct and/or concerted channel CH3COCH3+hv--> 2CH(3)+ CO (1') is considered to be unimportant.     

The operations of quantum logic gates with pure and mixed initial states

The implementations of quantum logic gates realized by the rovibrational states of a C(12)O(16) molecule in the X((1)Σ(+)) electronic ground state are investigated. Optimal laser fields are obtained by using the modified multitarget optimal theory (MTOCT) which combines the maxima of the cost functional and the fidelity for state and quantum process. The projection operator technique together with modified MTOCT is used to get optimal laser fields. If initial states of the quantum gate are pure states, states at target time approach well to ideal target states. However, if the initial states are mixed states, the target states do not approach well to ideal ones. The process fidelity is introduced to investigate the reliability of the quantum gate operation driven by the optimal laser field. We found that the quantum gates operate reliably whether the initial states are pure or mixed.     

Laser pulse control of exciton dynamics in a biological chromophore complex

Femtosecond laser pulse control of exciton dynamics in a biological chromophore complex is studied theoretically. The computations use the optimal control theory specified to open quantum systems and formulated in the framework of the rotating wave approximation. Based on the laser pulse induced formation of an excitonic wave packet the possibility to localize excitation energy at a certain chromophore within a photosynthetic antenna system (FMO complex of green bacteria) is investigated. Details of exciton dynamics driven by a polarization shaped pulse are discussed.     

Multidimensional density operator propagations in open systems: model studies on vibrational relaxations and surface sticking processes

An efficient method for the numerical treatment of multidimensional dynamics of open systems is presented: the multiconfiguration time-dependent Hartree (MCTDH) method extended to the propagation of density operators. With this method we investigate the relaxation process of a CO molecule adsorbed on a copper surface, i.e., CO/Cu(100), after the excitation with an infrared (IR) pulse. The interaction potential was taken from the literature. Lifetime estimations and thermalization studies were performed on the IR excited CO molecule. We were able to treat this system with all six degrees of freedom (DOF) and thus 12 dynamical variables, but most of our studies used a two or four DOF model. Finally, we demonstrate the applicability of MCTDH to the analysis of scattering processes in an open environment. We calculate sticking coefficients of a scattered particle to a model surface, the latter acting as heat bath. The surface corrugation and the initial particle energy have been varied, and six different relaxation strengths have been studied. These calculations were done under the inclusion of three DOFs: the two surface coordinates and the distance between the particle and the surface.     

Quantum reaction boundary to mediate reactions in laser fields

Dynamics of passage over a saddle is investigated for a quantum system under the effect of time-dependent external field (laser pulse). We utilize the recently developed theories of nonlinear dynamics in the saddle region, and extend them to incorporate both time-dependence of the external field and quantum mechanical effects of the system. Anharmonic couplings and laser fields with any functional form of time dependence are explicitly taken into account. As the theory is based on the Weyl expression of quantum mechanics, interpretation is facilitated by the classical phase space picture, while no "classical approximation" is involved. We introduce a quantum reactivity operator to extract the reactive part of the system. In a model system with an optimally controlled laser field for the reaction, it is found that the boundary of the reaction in the phase space, extracted by the reactivity operator, is modulated with time by the effect of the laser field, to "catch" the system excited in the reactant region, and then to "release" it into the product region. This method provides new insights in understanding the origin of optimal control of chemical reactions by laser fields.     

Optimal dynamic discrimination of similar quantum systems with time series data

Optimal dynamic discrimination (ODD) was proposed [Li et al., J. Phys. Chem. B 106, 8125 (2002)] as a paradigm for discriminating noninteracting similar quantum systems in a mixture. This paper extends the ODD concept to optimize a laser control pulse for guiding similar quantum systems such that each exhibits a distinct time series signal for maximum discrimination. The use of temporal data addresses various experimental difficulties, including noise in the laser pulse, signal detection errors, and finite time resolution in the signal. Simulations of ODD with time series data are presented to explore these effects. It is found that the use of an optimally chosen control pulse can significantly enhance the discrimination quality. The ODD technique is also adapted to the case where the sample contains an unknown background species.     

Optimal control of ultrafast laser driven many-electron dynamics in a polyatomic molecule: N-methyl-6-quinolone

We report time-dependent configuration interaction singles calculations for the ultrafast laser driven many-electron dynamics in a polyatomic molecule, N-methyl-6-quinolone. We employ optimal control theory to achieve a nearly state-selective excitation from the S(0) to the S(1) state, on a time scale of a few ( approximately 6) femtoseconds. The optimal control scheme is shown to correct for effects opposing a state-selective transition, such as multiphoton transitions and other, nonlinear phenomena, which are induced by the ultrashort and intense laser fields. In contrast, simple two-level pi pulses are not effective in state-selective excitations when very short pulses are used. Also, the dependence of multiphoton and nonlinear effects on the number of states included in the dynamical simulations is investigated.     

Laser control of vibrational excitation in carboxyhemoglobin: a quantum wave packet study

A coherent control algorithm is applied to obtain complex-shaped infrared laser pulses for the selective vibrational excitation of carbon monoxide at the active site of carbonmonoxyhemoglobin, modeled by the six-coordinated iron-porphyrin-imidazole-CO complex. The influence of the distal histidine is taken into account by an additional imidazole molecule. Density-functional theory is employed to calculate a multidimensional ground-state potential energy surface, and the vibrational dynamics as well as the laser interaction is described by quantum wave-packet calculations. At each instant in time, the optimal electric field is calculated and used for the subsequent quantum dynamics. The results presented show that the control scheme is applicable to complex systems and that it yields laser pulses with complex time-frequency structures, which, nevertheless, have a clear physical interpretation.