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In the presence of strong electric fields, the excited states of single-electron molecules and molecules with large transient dipoles become unstable because of anti-alignment, the rotation of the molecular axis perpendicular to the field vector, where bond hardening is not possible. We show how to overcome this problem by using circularly polarized electromagnetic fields. Using a full quantum description of the electronic, vibrational, and rotational degrees of freedom, we characterize the excited electronic state dressed by the field and analyze its dependence on the bond length and angle and the stability of its vibro-rotational eigenstates. Although the dynamics is metastable, most of the population remains trapped in this excited state for hundreds of femtoseconds, allowing quantum control. Contrary to what happens with linearly polarized fields, the photodissociation occurs along the initial molecular axis, not perpendicular to it.
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The aim of this study was to evaluate the psychological distress of Spanish airline pilots, a group of professionals undergoing an unprecedented work situation as a result of the Covid-19 pandemic. To do so, we administered the General Health Questionnaire-12 (GHQ-12). A total of 342 questionnaires were obtained, with the largest respondent age group being 41-50 years. The psychometric properties of the instrument were also evaluated, with an exploratory factor analysis revealing a unidimensional structure that explained 59.23% of the variance. The total score on the standard GHQ-12 was 4.54 ± 3.31 very close to the cut-off point established to determine psychological distress. The score increased among those unemployed and was also higher among pilots on furlough compared to those whose work situation was relatively normal. Furthermore, the reliability measured by the total Cronbach's alpha was above 0.8 of each across all employment status considered. These results show the desirability of conducting periodic psychological distress assessments of pilots so that effective measures can be implemented to ensure their psychological and socio-emotional well-being. Practitioner summary: This article evaluates psychological distress in a group of professionals that has received scant attention in the field. Moreover, it does so against the background of an atypical situation, evaluating the psychological distress suffered by pilots in different employment categories during the current severe crisis in the aviation sector.Abbreviations: CFI: comparative fit index; COPAC: Official College of Commercial Aviation Pilots; ECA: European Cockpit Association; EFA: exploratory factor analysis; GHQ-12: general health questionnaire-12; IATA: International Air Transport Association; KMO: Kaiser-Meyer-Olkin test; PA: optimal implementation of parallel analysis; ULS: unweighted least squares.
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Aviação , COVID-19 , Pilotos , Angústia Psicológica , Adulto , COVID-19/epidemiologia , Humanos , Pessoa de Meia-Idade , Pandemias , Psicometria , Reprodutibilidade dos Testes , Inquéritos e QuestionáriosRESUMO
We develop two novel models of the H2+ molecule and its isotopes from which we assess quantum-mechanically and semi-classically whether the molecule anti-aligns with the field in the first excited electronic state. The results from both models allow us to predict anti-alignment dynamics even for the HD+ isotope, which possesses a permanent dipole moment. The molecule dissociates at angles perpendicular to the field polarization in both the excited and the ground electronic state, as the population is exchanged through a conical intersection. The quantum mechanical dispersion of the initial state is sufficient to cause full dissociation. We conclude that the stabilization of these molecules in the excited state through bond-hardening under a strong field is highly unlikely.
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We predict anti-alignment dynamics in the excited state of H2+ or related homonuclear dimers in the presence of a strong field. This effect is a general indirect outcome of the strong transition dipole and large polarizabilities typically used to control or to induce alignment in the ground state. In the excited state, however, the polarizabilities have the opposite sign compared to those in the ground state, generating a torque that aligns the molecule perpendicular to the field, deeming any laser-control strategy impossible.
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The two-dimensional electron-nuclear Schrödinger equation using soft-core Coulomb potentials has been a cornerstone for modeling and predicting the behavior of one-active-electron diatomic molecules, particularly for processes where both bound and continuum states are important. The model, however, is computationally expensive to extend to more electron or nuclear coordinates. Here we propose use of the Ehrenfest approach to treat the nuclear motion, while the electronic motion is still solved by quantum propagation on a grid. In this work, we present results for a one-dimensional treatment of H2+, where the quantum and semiclassical dynamics can be directly compared, showing remarkably good agreement for a variety of situations. The advantage of the Ehrenfest approach is that it can be easily extended to treat as many nuclear degrees of freedom as needed.
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A comparative study of the ultrafast photodissociation dynamics of the dihalomethanes CH2ICl and CH2BrI has been carried out at 268 nm, around the maximum of the first absorption band, employing femtosecond velocity map ion imaging in conjunction with high level ab initio electronic structure calculations and full dimension on-the-fly trajectory calculations including surface hopping. Total translational energy distributions and angular distributions of the iodine fragments as well as reaction times for the C-I bond cleavage are presented and discussed along with the computed absorption spectra, potential energy curves and trajectories. The revealed dynamics is mainly governed by absorption to the 5A' state for CH2BrI while two dissociation pathways, through the 4A' or 5A' states, are in competition for CH2lCI. An anchor effect due to the substituent halogen atom (Br or Cl), which implies significant rotational motion of the dissociating molecule, characterizes the photodissociation in both dihalomethanes and leads to a remarkable rotational energy of the radical co-fragment. This energy flux into the internal degrees of freedom of the molecules is the main key factor governing the real time reaction dynamics.
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We study laser-driven isomerization reactions through an excited electronic state using the recently developed Geometrical Optimization procedure. Our goal is to analyze whether an initial wave packet in the ground state, with optimized amplitudes and phases, can be used to enhance the yield of the reaction at faster rates, driven by a single picosecond pulse or a pair of femtosecond pulses resonant with the electronic transition. We show that the symmetry of the system imposes limitations in the optimization procedure, such that the method rediscovers the pump-dump mechanism.
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Using numerical simulations of two-photon electronic absorption with femtosecond pulses in Na2 we show that: (i) it is possible to avoid the characteristic saturation or dumped Rabi oscillations in the yield of absorption by time-delaying the laser pulses; (ii) it is possible to accelerate the onset of adiabatic passage by using the vibrational coherence starting in a wave packet; and (iii) it is possible to prepare the initial wave packet in order to achieve full state-selective transitions with broadband pulses. The findings can be used, for instance, to achieve ultrafast adiabatic passage by light-induced potentials and understand its intrinsic robustness.
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We find a new mechanism of electronic population inversion using strong femtosecond pulses, where the transfer is mediated by vibrational motion on a light-induced potential. The process can be achieved with a single pulse tuning its frequency to the red of the Franck-Condon window. We show the determinant role that the gradient of the transition dipole moment can play on the dynamics, and extend the method to multiphoton processes with odd number of pulses. As an example, we show how the scheme can be applied to population inversion in Na2.
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Strong ultrashort laser pulses have opened new avenues for the manipulation of photochemical processes like photoisomerization or photodissociation. The presence of light intense enough to reshape the potential energy surfaces may steer the dynamics of both electrons and nuclei in new directions. A controlled laser pulse, precisely defined in terms of spectrum, time and intensity, is the essential tool in this type of approach to control chemical dynamics at a microscopic level. In this Perspective we examine the current strategies developed to achieve control of chemical processes with strong laser fields, as well as recent experimental advances that demonstrate that properties like the molecular absorption spectrum, the state lifetimes, the quantum yields and the velocity distributions in photodissociation processes can be controlled by the introduction of carefully designed strong laser fields.
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We have recently proposed a laser control scheme for ultrafast absorption in multilevel systems by parallel transfer (J. Phys. Chem. Lett. 2015, 6, 1724). In this work we develop an analytical model that better takes into account the main features of electronic absorption in molecules. We show that the initial vibrational coherence in the ground electronic state can be used to greatly enhance the rate and yield of absorption when ultrashort pulses are used, provided that the phases of the coherences are taken into account. On the contrary, the initial coherence plays no role in the opposite limit, when a single long pulse drives the optical transition. The theory is tested by numerical simulations in the first absorption band of Na2.
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We theoretically investigate the photon-echo spectroscopy of coupled electron-nuclear quantum dynamics. Two situations are treated. In the first case, the Born-Oppenheimer (adiabatic) approximation holds. It is then possible to interpret the two-dimensional (2D) spectra in terms of vibrational motion taking place in different electronic states. In particular, pure vibrational coherences which are related to oscillations in the time-dependent third-order polarization can be identified. This concept fails in the second case, where strong non-adiabatic coupling leads to the breakdown of the Born-Oppenheimer-approximation. Then, the 2D-spectra reveal a complicated vibronic structure and vibrational coherences cannot be disentangled from the electronic motion.
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INTRODUCTION: Outcome data of penile traction therapy (PTT) for the acute phase (AP) of Peyronie's disease (PD) have not been specifically studied. AIM: The aim of this study was to assess the effectiveness of a penile extender device for the treatment of patients with AP of PD. METHODS: A total of 55 patients underwent PTT for 6 months and were compared with 41 patients with AP of PD who did not receive active treatment ("no intervention group" [NIG]). MAIN OUTCOMES MEASURES: Pre- and posttreatment variables included degree of curvature, penile length and girth, pain by 0-10 cm visual analog scale (VAS), erectile function (EF) domain of the International Index of Erectile Function questionnaire, Erection Hardness Scale, Sexual Encounter Profile 2 question, and penile sonographic evaluation (only patients in the intervention group). RESULTS: The mean curvature decreased from 33° at baseline to 15° at 6 months and 13° at 9 months with a mean decrease 20° (P < 0.05) in the PTT group. VAS score for pain decreased from 5.5 to 2.5 after 6 months (P < 0.05). EF and erection hardness also improved significantly. The percentage of patients who were not able to achieve penetration decreased from 62% to 20% (P < 0.03). In the NIG, deformity increased significantly, stretched flaccid penile length decreased, VAS score for pain increased, and EF and erection hardness worsened. PTT was associated with the disappearance of sonographic plaques in 48% of patients. Furthermore, the need for surgery was reduced in 40% of patients who would otherwise have been candidates for surgery and simplified the complexity of the surgical procedure (from grafting to plication) in one out of every three patients. CONCLUSIONS: PTT seems an effective treatment for the AP of PD in terms of pain reduction, penile curvature decrease, and improvement in sexual function.
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Ereção Peniana , Induração Peniana/terapia , Tração/instrumentação , Adulto , Idoso , Humanos , Masculino , Pessoa de Meia-Idade , Induração Peniana/diagnóstico por imagem , Induração Peniana/fisiopatologia , Pênis/diagnóstico por imagem , Pênis/fisiopatologia , Pênis/cirurgia , Estudos Prospectivos , Resultado do Tratamento , Ultrassonografia , Adulto JovemRESUMO
By coherent control, the yield of photodissociation reactions can be maximized, starting in a suitable superposition of vibrational states. In ultrafast processes, the interfering pathways are born from the early vibrational coherences in the ground electronic potential. We interpret their effect from a purely classical picture, in which the correlation between the initial position and momentum helps to synchronize the vibrational dynamics at the Franck-Condon window when the pulse is at its maximum intensity. In the quantum domain, we show that this localization in time and space is mediated by dynamic squeezing of the wave packet.
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A laser-adiabatic manipulation of the bond (LAMB) scheme using moderately intense fields is proposed to induce and control large-amplitude oscillations in nuclear wave packets. The present scheme involves an ultrashort UV pump pulse to initially create a wave packet in an excited electronic state of the hydrogen molecular ion and a low-frequency control pulse, which is switched on after a given time, leading to controllable vibrational trapping. The choice of H2(+) as the target exploits the larger dipole values that molecular ions present as the internuclear distance increases. The amplitude and oscillation period of the wave packet is tuned by the field parameters of the control pulse, and more importantly, significant dissociation and ionization losses are prevented by keeping the laser intensities below hundreds of Terawatts. Our numerical simulations, based on the solution of the time-dependent Schrödinger equation, show that this control of the bond length is achieved in a wide range of moderate intensities and for relatively long pulse durations, from tens to hundreds of femtoseconds.
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Hidrogênio/química , Elétrons , Lasers , Espectrofotometria Ultravioleta , VibraçãoRESUMO
We propose a scheme to generate electric dipole moments in homonuclear molecular cations by creating, with an ultrashort pump pulse, a quantum superposition of vibrational states on electronic states strongly perturbed by very strong static electric fields. By field-induced molecular stabilization, the dipoles can reach values as large as 50 Debyes and oscillate on a time-scale comparable to that of the slow vibrational motion. We show that both the electric field and the pump pulse parameters can be used to control the amplitude and period of the oscillation, while preventing the molecule from ionizing or dissociating.
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By controlling the temporal and spatial features of light, we propose a novel protocol to prepare two-qubit entangling gates on atoms trapped at close distance, which could potentially speed up the operation of the gate from the sub-micro to the nanosecond scale. The protocol is robust to variations in the pulse areas and the position of the atoms, by virtue of the coherent properties of a dark state, which is used to drive the population through Rydberg states. From the time-domain perspective, the protocol generalizes the one proposed by Jaksch and coworkers [Jaksch et al., Phys. Rev. Lett., 2000, 85, 2208], with three pulses that operate symmetrically in time, but with different pulse areas. From the spatial-domain perspective, it uses structured light. We analyze the map of the gate fidelity, which forms rotated and distorted lattices in the solution space. Finally, we study the effect of an additional qubit to the gate performance and propose generalizations that operate with multi-pulse sequences.
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Recently, control over the bond length of a diatomic molecule with the use of parabolic chirped pulses was predicted on the basis of numerical calculations [Chang; et al. Phys. Rev. A 2010, 82, 063414]. To achieve the required bond elongation, a laser scheme was proposed that implies population inversion and vibrational trapping in a dissociative state. In this work we identify two regimes where the scheme works, called the strong and the weak adiabatic regimes. We define appropriate parameters to identify the thresholds where the different regimes operate. The strong adiabatic regime is characterized by a quasi-static process that requires longer pulses. The molecule is stabilized at a bond distance and at a time directly controlled by the pulse in a time-symmetrical way. In this work we analyze the degree of control over the period and elongation of the bond as a function of the pulse bandwidth. The weak adiabatic regime implies dynamic deformation of the bond, which allows for larger bond stretch and the use of shorter pulses. The dynamics is anharmonic and not time-symmetrical and the final state is a wave packet in the ground potential. We show how the vibrational energy of the wave packet can be controlled by changing the pulse duration.
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Extending the Shin-Metiu two-electron Hamiltonian, we construct a new Hamiltonian with effective singlet-triplet couplings. The Born-Oppenheimer electronic potentials and couplings are obtained for different parameters, and the laser-free dynamics is calculated with the full Hamiltonian and in the adiabatic limit. We compare the dynamics of the system using nuclear wave packets for different numbers of Born-Oppenheimer potentials and vibronic wave packets on a full 3-dimensional (two electron coordinates plus one nuclear coordinate) grid. Using strong fields, we show that it is possible to dynamically lock the spin state of the system by decoupling the singlet-triplet transition via a nonresonant dynamic Stark effect in the adiabatic limit. Although a similar spin-locking mechanism is observed in the dynamics of vibronic wave packets, multiphoton ionization cannot be neglected leading to the breakdown of the control scheme.
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Teoria Quântica , VibraçãoRESUMO
The dynamics of molecules under strong laser pulses is characterized by large Stark effects that modify and reshape the electronic potentials, known as laser-induced potentials (LIPs). If the time scale of the interaction is slow enough that the nuclear positions can adapt to these externally driven changes, the dynamics proceeds by adiabatic following, where the nuclei gain very little kinetic energy during the process. In this regime we show that the molecular dynamics can be simulated quite accurately by a semiclassical surface-hopping scheme formulated in the adiabatic representation. The nuclear motion is then influenced by the gradients of the laser-modified potentials, and nonadiabatic couplings are seen as transitions between the LIPs. As an example, we simulate the process of adiabatic passage by light induced potentials in Na(2) using the surface-hopping technique both in the diabatic representation based on molecular potentials and in the adiabatic representation based on LIPs, showing how the choice of the representation is crucial in reproducing the results obtained by exact quantum dynamical calculations.