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We report results on avalanche-like effect in up-conversion on Er ions-doped in KGW crystal for concentrations of 1 and 10−4 wt.%. Our experimental and theoretical data point to the conclusion, that avalanche-like behavior observed earlier at low trace concentrations [1] occurs also at much larger concentrations (up to 1%).

Nonlinear coupling of pumping rates in pump channels can produce effects very similar to the photon avalanche in up-conversion luminescence in the absence of a true avalanche. Stationary luminescence intensity can depend on the pump intensity practically in the same way. Here we show that time-dynamics for true avalanche and for avalanche-like processes are drastically different. Based on measuring the development times of stationary luminescence for several pump intensities, a simple test is proposed to reveal the nonlinear process underlying the observed avalanche-like effect.

Here we report and discuss the avalanche-like up-conversion behavior in absence of the avalanche. We experimentally observed significant changes in the slope of the curve for the intensity dependence of up-conversion luminescence of erbium ions in the green band (520-560 nm) on the pump intensity of the diode laser. Such changes are typical for the photon avalanche. However, the concentration of erbium ions is insufficient for an efficient exchange of energy between them, and the excitation of a photon avalanche is not possible. Using a simple three-level approximation of the up-conversion process model, we have shown that the observed avalanche-like luminescence process can also occur in the absence of a photon avalanche due to the nonlinear relation between the efficiency of two pumping channels of erbium ions caused by the intensity dependence of the pump spectrum.

In this work an exactly solvable model of N two-level systems interacting with a single bosonic dephasing reservoir is considered to unravel the role played by collective non-Markovian dephasing. We show that phase estimation with entangled states for this model can exceed the standard quantum limit and demonstrate Heisenberg scaling with the number of atoms for an arbitrary temperature. For a certain class of reservoir densities of states decoherence can be suppressed in the limit of large number of atoms and the Heisenberg limit can be restored for arbitrary interrogation times. We identify the second class of densities when the Heisenberg scaling can be restored for any finite interrogation time. We also find the third class of densities when the standard quantum limit can be exceeded only on the initial stage of dynamics in the Zeno-regime., Comment: Accepted to Phys. Rev. A

The optically induced fragmentation of deuterium chloride ions (DCl+) has been investigated by means of computer simulation within the Schrodinger wave-function formalism for three lowest 2gV electronic states coupled by IR-laser pulse with 34.6 fs duration. We demonstrate that the dependence of dissociation yields as function of the carrier envelope phase (CEP) of few-cycle laser pulses can be fundamentally different (2π or π periodicity) for oriented and aligned ions. To achieve a deep insight in mutual electronic nuclear dynamics we investigate the time dependence of fragmentation yields and vibrational populations as well as the space-time representation of electronic wave function probability dynamics for few selected cases. Ultimately we suggest an approach for distinguishing oriented from aligned molecular ensembles. Further-more the current concept provides access to directional product ion beams (D+ or/and Cl+) by proper selection of the CEP.

Dynamical implications of the dissociation of a molecular ion under the influence of interferometrically generated light fields have been investigated by numerical solution of time dependent Schrödinger equations. As an example the dissociation of DCl+ ions by means of two interfering 7 fs laser pulses at 800 nm has been chosen. We demonstrate that product branching ratios D+:Cl+ can be manipulated from 10:1 to 1:10 not only by adjusting the appropriate delay time in the time-shifted two-pulse approach, but also by choosing the proper carrier envelope phase (CEP) of the two partial light fields. The effects of the phase shift related to the time shift and that of the CEP can be clearly distinguished.

The principles of creating multifunctional safety systems (MFSS) based on mathematical models with Markov properties are considered. The applicability of such models for the analysis of the safety of the created systems and their effectiveness is substantiated. The method of this analysis and the results of its testing are discussed. The variant of IFSB implementation in the conditions of the operating coal-mining enterprise is given. The functional scheme, data scheme and operating modes of the MFSS are given. The automated workplace of the industrial safety controller is described.

Previous quantum dynamical investigations of resonant versus off-resonant reactivity are extended from the gas phase to a quantum solid, using the simple model of Korolkov et al. [M.V. Korolkov, J. Manz, A. Schild, J. Phys. Chem. A 113 (2009) 7630] for the title reaction. Systematic empirical simulations discover that the different reaction mechanisms cause formations of the products with different “universal” i.e., exponential versus error-function type time evolutions, respectively. The wavepacket dynamics suggests that rich additional patterns of the time-dependent yields are caused by interferences of resonant plus non-resonant components. At long times, the resonance remains as exclusive source feeding product formation. By analogy with work of Eli Pollak for resonances in the gas phase, the resonance wavefunctions correspond to unstable classical periodic orbits describing hydrogen transfer Cl · H 2 ∗ ⇋ ClH · H ∗ in the resonant collision complex.

The interaction of a molecule with the laser field generated by two time-shifted interfering femtosecond laser pulses is shown to control electron and nuclear dynamics. We demonstrate that the product yields caused by the interferometric dissociation carry the signature of time dependent electronic polarization due to the correlated electronic and nuclear dynamics induced in the region of partial overlap of two laser pulses. Thus, the two pulse technique provides a powerful tool for bridging the gap between electron and nuclear dynamics.

Recent experimental investigations by the group of D. T. Anderson (Kettwich, S. C.; Raston, P. L.; Anderson, D. T. J. Phys. Chem. A 2009, 113, DOI 10.1021/jp811206a) show that the reaction Cl + H(2) --HCl + H in the para-H(2) crystal can be induced by infrared (IR) + ultraviolet (UV) coirradiations causing vibrational pre-excitation of the molecular reactant, H(2)(v=1), and generation of the atomic reactant, Cl((2)P(3/2)), by near-resonant photodissociation of a matrix-isolated Cl(2) molecule in the C (1)Pi(u) state, respectively. The corresponding reaction probability P(v=1) for the reactants Cl + H(2)(v=1) is approximately 0.15; this is approximately 25 times larger than P(v=0) for Cl + H(2)(v=0) (as initiated by pure UV irradiation). We present a simple three-step quantum model which accounts for some important parts of the experimental results and allows predictions for other scenarios, for example, UV photodissociation of the Cl(2) molecule by a laser pulse. The first step, vibrational pre-excitation of H(2), yields the molecular initial state which is described using the Einstein model of the para-H(2) crystal. The second step, photodissociation of Cl(2), generates the Cl((2)P(3/2)) atom approaching H(2)(v=1). In the third step, Cl reacts with H(2)(v=1) much more efficiently than with H(2)(v=0) close to threshold. The ultrashort time domains (approximately 100 fs) of steps 2 plus 3 support one- and then two-dimensional models of photodissociation of Cl(2) by short laser pulses and of the subsequent reaction of the system Cl-H-H embedded in frozen environments. The widths of the corresponding wave function describing the translational motion of the reactants is revealed as a significant parameter which is determined not only by the duration of the laser pulse but, even more importantly, by the width of the Gaussian-type distribution of the center of mass of the H(2) molecule in its Einstein cell. As a consequence, the resulting P(v) are quite robust versus variations of the UV pulse durations, allowing extrapolations to continuous wave irradiation. Quantum dynamics simulations of the reaction reveal that the experimental results are due to energetic and dynamical effects.

The optically induced fragmentation of deuterium chloride ions (DCl + ) has been investigated by solving coupled time dependent Schrodinger equations. We demonstrate that the branching ratio D + :Cl + of competing reaction channels leading to either D + or Cl + can be controlled by up to a factor of 100 by means of the carrier envelope phase (CEP). This CEP effect depends on the wavelength, the intensity and on the chirp of the fs laser pulses.

Photofragmentation of DCl+ ions alternatively leads to the formation of D+ + Cl or Cl+ + D in competing reaction channels. The branching ratio of the product yields D+/Cl+ has been investigated theoretically by numerically solving coupled time dependent Schrodinger equations and experimentally by femtosecond (fs) dissociative ionization of DCl. The theoretical analysis shows that this branching ratio increases step-like at intensities, which characteristically depend on the initial vibrational state for nonresonant multiphoton excitation. In general the threshold decreases with increasing initial vibrational quantum number. Experimental studies exhibit a similar step-like behavior of the D+/Cl+ branching ratio. Here the intensity at which the step occurs characteristically depends on the chirp of the fs-laser pulses, suggesting that different chirp may lead to intermediate DCl+ ions differing in the effective vibrational quantum number.

The competition between direct dissociation and predissociation in DCl(+) ions prepared in the A(2)Σ(+) state has been investigated numerically by solving the time dependent Schrodinger equation. This work concentrates on the rovibronic states (vA;NA) with vA = 8 and NA = 60-65, which are close to the top of a centrifugal barrier. We find that the relative yield of D(+) (by direct dissociation) and Cl(+) (by predissociation) strongly depends on the excitation frequency, intensity, and duration. Investigation of the time dependence of the product yields provides evidence for significant multichannel interactions.

Starting from a diatomics-in-molecules Hamiltonian description of the valence states of Cl 2 embedded in an argon matrix, classical trajectory simulations are utilized to establish a one-dimensional model for the photodissociation dynamics in three selected singlet and triplet states which is valid during approximately 150 fs after Franck–Condon excitations, i.e. before the Cl atoms approach the neighbouring Ar atoms. Using this one-dimensional model which describes the dynamics of the Cl–Cl bond length in the frozen argon lattice we carry out quantum dynamics simulations of the laser pulse control of the electronic spin with femtosecond time resolution and sub-Angstrom spatial localization by means of simultaneous excitation of wave packets on the singlet and triplet potential curves starting from a vibrational superposition state in the electronic ground state. It is shown that the latter can be prepared by a pump–dump pulse sequence.

The state-selective predissociation spectroscopy of HCl+ and DCl+ ions has been investigated in a two color double-resonance experiment. Ions are formed in the vibronic ground state X 2Π3/2 by the...

Two coherent sequential IR+UV laser pulses may be used to generate two time-dependent nuclear wave functions in electronic excited triplet and singlet states via single (UV) and two photon (IR+UV) excitation pathways, exploiting spin-orbit coupling and vibrational pre-excitation, respectively. These wave functions evolve from different Franck-Condon domains until they overlap in a domain of bond stretching with efficient intersystem crossing. Here, the coherence of the laser pulses is turned into optimal interferences of the wave packets, yielding the total wave packet at the target place, time, and with dominant target spin. The time resolution of spin control is few femtoseconds. The mechanism is demonstrated by means of quantum model simulations for ClF in an Ar matrix.

Quantum dynamical simulations of ultrafast processes of F2 in an Ar matrix induced by a pump laser pulse show that photoexcitation (i) is followed by (ii) a stretch of the dissociative bond, (iii) collision with, vibrational excitations of, and possible exit through the nearest neighbour atoms of the surrounding cage, and (iv) finally, subsequent rescattering of the dissociated atoms causing vibrations of additional matrix atoms. If the laser pulse ended before the onset of process (iii), the initial steps (i) and (ii) are similar to photodissociations in the gas phase and are, therefore, well described in terms of the wavepacket dynamics of the diatomic molecule in reduced dimensionality. For specific symmetry constraints, the initial processes (i), (ii), and (iii) may be described in terms of just 1- and 2- or 3-dimensional wavepacket dynamics, respectively. At the end of the laser pulse, this low-dimensional wavepacket may serve to prepare the high-dimensional one for the subsequent laser-free dynamics of the total system.

The possibility of spin–orbit induced association reactions controlled by optimized femtosecond laser pulses is demonstrated for the example of Br + ( 3 P )+ H ( 2 S )→ HBr + ( X 2 Π/ A 2 Σ + ) 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.

From the analysis of steps observed in single rotational transitions of predissociation spectra the dissociation energy of HCl+ has been determined as Do(HCl+) = 37 536.7 ± 0.5 cm−1. Combining this value with accurate literature data on the ionization energy of HCl and Cl we derive a new value for the dissociation energy of neutral HCl, Do(HCl) = 35 747.2 ± 1.2 cm−1. Finally by combination with the dissociation energy of Cl2 and H2 we obtain an improved 0 K heat of formation of HCl, ΔfH°(HCl, 0 K) = −91.99 ± 0.02 kJ mol−1. These results are believed to be relevant for all thermochemical investigations involving the HCl molecule.

Ultrafast spin-flip is used to monitor the subpicosecond intersystem crossing dynamics from the 1Π to the 3Π state following photodissociation of ClF isolated in an Ar matrix by means of pump–probe spectroscopy. After photoexcitation of the 1Π state analysis of the populations of triplet states shows that about 50 percent of the spin-flip occurs during the first bond stretch which takes about 250 fs. The early time dynamics of the Cl–F bond in an Ar matrix is investigated theoretically by selecting representative singlet and triplet excited states from a diatomics-in-molecules Hamiltonian. In a one-dimensional model, wave-packet simulations for the first excursion are performed which give a lower limit of about 60 fs for the spin-flip process. The ultrafast spin flip is supported by the caging of the wave packet by the neighboring Ar atoms. Already before collision of the F and Ar atoms the rather large energy gap between the 1Π and 3Π states in the Franck–Condon region is reduced rapidly to near degeneracy. As a consequence the spin–orbit interaction becomes dominant, inducing more than 40% admixture of the triplet character in the 1Π state. Subsequent kinetic energy transfer from ClF to Ar, not yet included in the model, should slow down the Cl and F atoms on their way back toward shorter bond distances, implying stabilization of the wave packet in the 3Π state, where it is monitored by the probe laser pulse.

The electronic excitation induced by ultrashort laser pulses and the subsequent photodissociation dynamics of molecular fluorine in an argon matrix are studied. The interactions of photofragments and host atoms are modeled using a Diatomics-In-Molecule Hamiltonian. Two types of methods are compared: Quantum-classical simulations where the nuclei are treated classically, with surface-hopping algorithms to describe either radiative or non-radiative transitions between different electronic states. Fully quantum-mechanical simulations, but for a model system of reduced dimensionality, in which the two most essential degrees of freedom are considered. Some of the main results are: The sequential energy transfer events from the photoexcited F2 into the lattice modes are such that the ``reduced dimensionality'' model is valid for the first 200 fs. This, in turn, allows us to use the quantum results to investigate the details of the excitation process with short laser pulses. Thus, it also serves as a reference for the quantum-classical ``surface hopping'' model of the excitation process. Moreover, it supports the validity of a laser pulse control strategy developed on the basis of the ``reduced dimensionality'' model. Both in the quantum and quantum-classical simulations, the separation of the F atoms following photodissociation does not exceed 20 bohr. The cage exit mechanisms appear qualitatively similar in the two sets of simulations but quantum effects are quantitatively important. Nonlinear effects are important in determining the photoexcitation yield. In summary, this paper demonstrates that quantum-classical simulations combined with reduced dimensionality quantum calculations can be a powerful approach to the analysis and control of the dynamics of complex systems.

The properties of HCl+ ions formed in the vibronic ground state 2Π3/2 (″ = 0) ia the R(1) pump line of the f3Δ2←1Σ+ REMPI spectrum have been investigated. In the first experiment the rotational state distribution of these ions has been determined by photoexcitation into the A2Σ+(′ = 7) state, which can predissociate. 73% of the HCl+ ions are found in the N″ = 0 state, 23% in the N″ = 1 and 4% in the N″ = 2 state. This experiment also yields the spectroscopic parameters of the A2Σ+(′ = 7) state and information on the rotational dependence of the predissociation lifetimes of this state. The threshold for predissociation occurs between the N′ = 0, J′ = 1/2 and the N′ = 1, J′ = 1/2 state, leading to a new dissociation energy of the HCl+ ion of D0 = 37536.5 cm−1±5 cm−1. In the second experiment these state-selected HCl+ ions are investigated in an ion–molecule reaction with carbon monoxide. In this reaction very efficient proton transfer leads to the formation of HCO+ with a rate constant close to the Langevin limit.

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.

The spin–orbit induced predissociation dynamics of HCl + and HBr + ions have been investigated by numerical solution of four coupled time-dependent Schrodinger equations based on ab initio potential energy data. For HCl + exponential decay dominates for all vibrational levels in the electronic excited 2 Σ + state. For HBr + pronounced nonexponential decay occurs due to significant multichannel competition. The comparison of temporal and spectral representations of the dynamics reveals that the derivation of dynamic information from experimental frequency domain spectra may be difficult in the case of multichannel competition.

The predissociation dynamics of the vibrational eigenstates of hydrogen bromide ions (HBr + ) in the first excited electronic state A 2 Σ + which occurs via coupling to three repulsive ( 4 Σ − , 2 Σ − , and 4 Π ) states has been investigated by direct solution of four coupled time-dependent Schrodinger equations. The analysis shows multi-exponential decay for most of the predissociating vibrational states. The lifetime of these states decreases by several orders of magnitude from τ v =2 ≫1 ns to τ v =5 ≈17 fs. For even higher vibrational states lifetimes are increasing again up to the order of 100 fs. The contribution of the individual repulsive states to the predissociation dynamics is found to change as a function of time and of the vibrational level. The competition between the contributions of the repulsive states is most important during the first ∼10 fs. Beyond this one repulsive state in general dominates. Finally the shifting of vibrational `eigenenergies' of the A 2 Σ + state by spin–orbit interaction and their broadening due to the fast predissociation are analyzed.

The quantum dynamics of photoassociative collisions O(3P) + H(2S) controlled by picosecond laser pulses is explored in the ground (X 2 Π ) and excited (A 2 Σ + ) electronic states. Coupled Schrodinger 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.

Vibrationally state-selective complete population transfer from the ground electronic state to the excited electronic state is demonstrated on a femtosecond time scale for the ${X}^{2}\ensuremath{\Pi}$ and ${A}^{2}{\ensuremath{\Sigma}}^{+}$ states of the OH molecule by means of computer simulation within the Schr\"odinger wave-function formalism. State-selective population transfer within the excited electronic state ${A}^{2}{\ensuremath{\Sigma}}^{+}$ of OH is demonstrated as well. These processes are controlled by shaped linearly polarized femtosecond laser pulses in the ultraviolet and in the infrared region, correspondingly, with the probability of the population transfer being close to 100%.

Ultrafast state-selective vibrational excitation and dissociation controlled by shaped subpicosecond infrared laser pulses is investigated within the reduced density matrix formalism beyond a Markov-type approximation for diatomic molecules, which are coupled to an unobserved quasiresonant environment. Dissipative quantum dynamics in a classical electric field is simulated for discrete vibrational bound states and for dissociative continuum states of a one-dimensional dissociative Morse oscillator, tailored to the local OH bond of the H2O and HOD molecules in the electronic ground state. Flexible laser control schemes are developed and demonstrated on a picosecond time scale, which enable one either to localize the population at prescribed high-lying discrete vibrational levels of OH, up to those close to the dissociation threshold, with the probability up to 70–80 % without substantial dissociation or, alternatively, achieve the dissociation yield of about 75%, while the strength of the quasiresonant molecule-environment coupling results in subpicosecond lifetimes of the vibrational bound states. The optimal laser control schemes may include the superposition of up to four subpicosecond laser pulses. @S1050-2947~97!02710-8#

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, effecitve (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 one to design the energy distribution of the scattered atoms

An overview of the current state of the art in the laser control of molecular dynamics is presented with a special emphasis on the ultrafast vibrationally state-selective processes controlled by short and shaped infrared laser pulses. Ultrafast state-selective vibrational dynamics and dissociation of isolated diatomic molecules in the electronic ground state under the control of intense and shaped infrared laser pulses of picosecond and femtosecond duration is investigated within the Schrodinger wavefunction formalism. The laser driven dissipative dynamics is investigated within the reduced density matrix formalism beyond and within a Markov-type approximation for the ultrafast state-selective excitation of diatomic molecules, which are coupled to an unobserved quasi-resonant thermal environment. Quantum dynamics in a classical electric field is simulated for a one-dimensional Morse oscillator, representing the local OH bond of the H2O and HOD molecules in the electronic ground state. Flexible tools of optimal laser control are developed and demonstrated on a picosecond timescale, which enable to localize the population with a very high probability at any prescribed vibrational level of OH, including those close to the dissociation threshold, without substantial dissociation. Comparative analysis of the Markovian and non-Markovian dissipative quantum dynamics reveals that the Markov approximation results in a pronounced decrease of a predicted probability for ultrafast selective preparation of very high vibrational bound states. The laser-controlled dissociation from selectively prepared high vibrational bound states is investigated for a wide range of the laser carrier frequencies, revealing the role of the phase of the dissociating laser pulse. In the limiting case of small laser frequencies, for half-cycle pulses, a spatial squeezing of highly excited molecules is discovered. It is demonstrated that the optimally controlled dissociation may be very efficient, and the dissociation probability may approach the maximal value. Quantum dynamics of vibrationally state-selective association of a diatomic molecule in the electronic ground state controlled by shaped sub-picosecond infrared laser pulse is investigated by means of representative wavepackets. It is shown, in particular, that a colliding pair of O and H atoms can be transferred selectively into a prespecified vibrational bound state of OH(ν). Optimal design of the laser field controlling this process results in a high association probability with a very high vibrational state-selectivity.

An efficient approach to control isomerization reactions by ultrashort infrared laser pulses in the presence of a thermal environment is developed and demonstrated by means of model simulations within the reduced density matrix formalism beyond a Markov‐type approximation for a picosecond Cope rearrangement of 2,6‐dicyanoethyl‐methylsemibullvalene coupled to a quasi‐resonant environment. The population transfer from the reactant state via the delocalized transition state to the product state is accomplished by two picosecond infrared laser pulses with a probability up to 80% despite the rather strong coupling to the environment, which reduces the lifetime of the transition state into the femtosecond time domain. Simulations, carried out for helium (4 K), nitrogen (77.2 K) and room (300 K) temperatures, show that low temperatures are preferable for state‐selective laser control of isomerization reactions.

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.

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 Schrodinger 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% selective 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 contains 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.

Ultrafast state-selective manipulation of populations under the control of shaped picosecond infrared laser pulses is investigated by means of computer simulations within the reduced density matrix formalism beyond the Markov approximation for the HOD molecule coupled to an unobserved quasi-resonant environment. The laser-driven dissipative quantum dynamics in a classical electric field is simulated for discrete vibrational levels within a two-dimensional model of the HOD stretches in the electronic ground state. Efficient population transfer with the probability up to 80-90% is demonstrated on a picosecond time scale in the presence of the environmental degrees of freedom which reduce the lifetimes of vibrational bound states into a picosecond time domain.

An efficient laser control scheme for ultrafast state-selective preparation of vibrationally excited molecules close to the dissociation threshold with ultrashort infrared laser pulses has been developed and demonstrated by means of computer simulations for a one-dimensional dissociative model of OH in the electronic ground state. The control scheme for OH may include up to four laser pulses with properly optimized amplitudes, carrier frequencies, and overlaps. Simulations of the quantum dynamics in the classical laser field show that any prescribed high vibrational level of OH can be populated with selectivity close to 100%.

Six isotope effects (i)-(vi) are discovered for the reactions Cl + H(2)(ν) → HCl + H in solid para-H(2) ( 1 ) versus Cl + D(2)(ν) → DCl + D in ortho-D(2) ( 2 ), by means of quantum reaction dynamics simulations, within the frame of our simple model ( J. Phys. Chem. A 2009 , 113 , 7630 . ). Experimentally, the reactions may be initiated for ν = 0 and ν ≥ 1, by means of "UV only" photodissociation of the matrix-isolated precursor, Cl(2), or by "IR + UV" coirradiation ( Kettwich , S. C. , Raston , P. L. , and Anderson , D. T. J. Phys. Chem. A 2009 , 113 , 7621 . ), respectively. Specifically, (i) various shape and Feshbach reaction resonances correlate with vibrational thresholds of reactants and products, due to the near-thermoneutrality and low barrier of the system. The energetic density of resonances increases as the square root of mass, from M(X) = M(H) to M(D). (ii) The state selective reaction ( 1 ), ν = 1, is supported by a shape resonance, whereas this type of resonance is absent in ( 2 ), ν = 1. As a consequence, time-resolved measurements should monitor different three-step versus direct error-function type evolutions of the formation of the products. (iii) The effective barrier is lower for reaction 1 , ν = 0, enhancing the tunneling rate, as compared to that for reaction 2 , ν = 0. (iv) For reference, the reaction probabilities P versus total energy E(tot) in the gas exhibit sharp resonance peaks or zigzag behaviors of the reaction probability P versus total energy, near the levels of resonances ( Persky , A. and Baer , M. J. Chem. Phys . 1974 , 60 , 133 . ). These features tend to be washed out and broadened for reaction 1 , and even more so for reaction 2 . For comparison, they disappear for reactions in classical solids. (v) The slopes of P versus E(tot) below the potential barrier increase more steeply for reaction 1 , ν = 0, than for reaction 2 , ν = 0. This enhances the tunneling rate of the heavier isotopomer, reaction 2 , ν = 0, compared to that for reaction 1 . (vi) For a given value of the UV frequency, the translational energy E(trans) increases with mass M(X). Again, this effect supports tunneling of the heavier isotopomer. The isotope effects (i)-(iii), (iv)-(v), and (vi) may be classified as energetic, translational amplitude, and kinematic, respectively. Specifically, the effects (iv)-(v) are due to a systematic decrease of the amplitudes of translational motions of the reactant molecules, from quasi infinite in the gas via still rather large values of para-H(2)(ν) and smaller values for ortho-D(2)(ν) to very small values in classical solids. These isotope effects are special phenomena in quantum solids, which do not occur, neither in the gas phase nor in classical solids. Quantitative predictions, e.g., for the effects of increasing UV frequency on the ratio of reactions probabilities for the UV only versus IR + UV experiments, must account for the interplay of various isotope effects, e.g., (vi) combined with the antagonistic effects (iii) versus (iv) and (v).

The preparation of matrix isolated homonuclear diatomic molecules in a vibrational superposition state c0Phie=1,v=0+cjPhie=1,v=j, with large (|c0|2 approximately 1) plus small contributions (|cj|21) of the ground v=0 and specific v=j low excited vibrational eigenstates, respectively, in the electronic ground (e=1) state, and without any net population transfer to electronic excited (e1) states, is an important challenge; it serves as a prerequisite for coherent spin control. For this purpose, the authors investigate two scenarios of laser pulse control, involving sequential or intrapulse pump- and dump-type transitions via excited vibronic states Phiex,k with a dominant singlet or triplet character. The mechanisms are demonstrated by means of quantum simulations for representative nuclear wave packets on coupled potential energy surfaces, using as an example a one-dimensional model for Cl2 in an Ar matrix. A simple three-state model (including Phi1,0, Phi1,j and Phiex,k) allows illuminating analyses and efficient determinations of the parameters of the laser pulses based on the values of the transition energies and dipole couplings of the transient state which are derived from the absorption spectra.

The electronic structure of the HCl(+) molecular ion has been calculated using the general-R symmetry-adapted-cluster configuration interaction (SAC-CI) method. The authors present the potential energy curves, dipole moments, and transition dipole moments for a series of doublet states. The data are compared with the previous CASSCF and MCSCF calculations. The SAC-CI results reproduce quite well the data available in literature and extend the knowledge on the HCl(+) electronic structure for several higher states. The calculated R-dependent behavior of both dipole moments and transition dipole moments for a series of bound and unbound states reveals an intricate dissociation process at intermediate distances (RR(e)). The pronounced maxima in transition dipole moment (TDM) describing transitions into high electronic states (X (2)Pi--3 (2)Pi, X (2)Pi--3 (2)Sigma, 2 (2)Pi--3 (2)Pi, 3 (2)Pi--4 (2)Pi) occur at different interatomic separations. Such TDM features are promising for selection of excitation pathways and, consequently, for an optimal control of the dissociation products.

The predissociation dynamics of hydrogen chloride ions (HCl + and DCl + ) in the electronic A 2 Σ + state has been investigated by solving the time dependent Schrodinger equation. The predissociation lifetime is shown to strongly depend on the vibrational and the rotational quantum number, with quasi-periodic oscillations. Rovibronic states, which exhibit lifetimes about 1 order of magnitude larger than those of neighboring states, are termed rotational islands of stability (RIS). These RIS can be correlated with characteristic reference energies, e.g., the difference between rovibronic eigenenergy and the energy of crossing of rotronic bound and repulsive potentials. The origin of these RIS is illustrated by model studies of the positions of the nuclear wave functions involved.

The prospect of controlling the photofragmentation of deuterium chloride ions (DCl+) via strong ultrashort IR laser pulses has been investigated by a numerical solution of coupled Schrodinger equations. The calculations provide evidence that the ratio of product ion yields Cl+ versus D+ can be manipulated by an appropriate choice of laser pulse parameters, in particular, central laser frequency, pulse duration, intensity, and chirp. The analysis of time-dependent populations reveals competition between intra- and interelectronic state excitations, enabling the understanding of quantum control at the molecular level.

DBF laser of this type is based on the modulation of activator concentration being introduced into the crystal during the growth process.1 As a result, spatial periodic structures of activator concentration N a ( z ) = ∑ N m a ( z ) ⋅ ℓ i m q z and refractive index n ( z ) = ∑ n m ( z ) ⋅ ℓ i m q z are formed with the period L (q = 2π/Λ) and profile determined by crystal growth conditions.2 Rescattering of the counter-running waves of generation on the structures leads to the DFB.

A semiclassical treatment of transient behavior of a gain-coupled, distributed feedback laser is developed. The nonlinear response of the lasing medium to the spatially periodic pump and the effect of self-induced grating are involved in the theory. The influence of a noise signal value on the generation kinetics is demonstrated. The possibility of practically unidirectional lasing is also shown.

possible to process rapidly extensive data from spectroscopic studies of an erosion laser plume from a copper target. The obtained space-time distributions of the plasma parameters showed that particles of the liquid-drop phase of the target material flow into the erosion flame. Absorbing the laser radiation, these particles are additionally vaporized and increase the pressure and density of the plume vapor near the surface of the target right up to distances of 10-12 mm. This can substantially increase the absorption of the incident laser radiation by the erosion plume compared with the plume forming owing to adiabatic expansion of transparent vapor.