Collision-induced Effects Research Articles

Elucidation of rotational-interaction coupling and collision-induced effects in rovibrational transitions of β-N2O isotopologue at 7.8 µm mid-infrared region by cavity ring-down spectroscopy

High-sensitive cavity ring-down spectroscopy (CRDS) coupled with a cw-quantum cascade laser operating at 7.8 μm mid-infrared (MIR) region has been employed to investigate the rovibrational interaction coupling for various MIR rotational transitions of the P-and R-branches in the ν1 fundamental vibrational band (1000 ← 0000) of the β-site-specific isotopologue of nitrous oxide (β-N2O) i.e., 15N14N16O. The coupled rotational interaction was experimentally quantified from the high-resolution CRDS data and a data-driven approach was taken for the approximation of the Herman-Wallis series. Moreover, J-dependent pressure-broadened absorptions and their collision lifetimes in response to foreign-perturbing gas molecules were investigated to understand the collision-induced rotational quantum effect in β-N2O molecule. This study reveals an experimental elucidation of the fundamental infrared physics underlying rovibrational interaction and its coupling to the vibrational and rotational degrees of freedom for a non-centrosymmetric linear polyatomic molecule possessing a permanent dipole moment. Moreover, the experimentally probed interference-free spectral lines of β-N2O molecule attributing different spectroscopic signatures in the MIR region may drive new applications in environmental monitoring, biological and biomedical diagnostics in the future.

Terahertz plasma oscillations and dissipating solitary pulses in electron–hole semiconductor plasmas

Abstract Linearized modes of oscillation in terahertz range and weakly dissipating electrostatic solitary pulses are studied in semiconductor plasmas in the framework of quantum hydrodynamics. Many-particle effect is expressed in the local density approximation with the help of exchange-correlation potential and the species space charge effect is included through Poisson’s equation. Using reductive perturbation technique, damped Korteweg de-Vries equations is derived with a linear damping term arising due to electron (hole)–phonon collisions. Time evolution of solitary acoustic pulses is presented analytically and numerically. Typical values corresponding to GaAs, GaSb, InP and GaN semiconductors are used for parametric analysis and pulse profile with collision-induced dissipation and quantum effects of statistical pressure, Bohm potential and exchange-correlation potential. The pulses are stable and can withstand perturbations for a considerable time before damping.

Strong effects of fast collisions between pulsed optical beams in a linear medium with weak cubic loss

We investigate fast collisions between pulsed optical beams in a linear medium with weak cubic loss that arises due to nondegenerate two-photon absorption. We introduce a perturbation method with two small parameters and use it to obtain general formulas for the collision-induced changes in the pulsed-beam’s shape and amplitude. Moreover, we use the method to design and characterize collision setups that lead to strong localized and nonlocalized intensity reduction effects. The values of the collision-induced changes in the pulsed-beam’s shape in both setups are larger by one to two orders of magnitude compared with the values obtained in previous studies of fast two-pulse collisions. Furthermore, we show that for nonlocalized setups, the graph of the collision-induced amplitude shift vs the difference between the first-order dispersion coefficients for the two pulsed-beams has two local minima. This finding represents the first observation of a deviation of the graph from the common funnel shape that was obtained in all previous studies of fast two-pulse collisions in the presence of weak nonlinear loss. The predictions of our perturbation theory are in good agreement with results of numerical simulations with the perturbed linear propagation model, despite the strong collision-induced effects. Our results can be useful for multisequence optical communication links and for reshaping of pulsed optical beams.

Precise predictions of H2O line shapes over a wide pressure range using simulations corrected by a single measurement

In this work, we show that precise predictions of the shapes of H2O rovibrational lines broadened by N2, over a wide pressure range, can be made using simulations corrected by a single measurement. For that, we use the partially-correlated speed-dependent Keilson–Storer (pcsdKS) model whose parameters are deduced from molecular dynamics simulations and semi-classical calculations. This model takes into account the collision-induced velocity-changes effects, the speed dependences of the collisional line width and shift as well as the correlation between velocity and internal-state changes. For each considered transition, the model is corrected by using a parameter deduced from its broadening coefficient measured for a single pressure. The corrected-pcsdKS model is then used to simulate spectra for a wide pressure range. Direct comparisons of the corrected-pcsdKS calculated and measured spectra of 5 rovibrational lines of H2O for various pressures, from 0.1 to 1.2 atm, show very good agreements. Their maximum differences are in most cases well below 1%, much smaller than residuals obtained when fitting the measurements with the Voigt line shape. This shows that the present procedure can be used to predict H2O line shapes for various pressure conditions and thus the simulated spectra can be used to deduce the refined line-shape parameters to complete spectroscopic databases, in the absence of relevant experimental values.

Early Mars serpentinization‐derived CH4 reservoirs, H2‐induced warming and paleopressure evolution

AbstractCH4 has been observed on Mars both by remote sensing and in situ during the past 15 yr. It could have been produced by early Mars serpentinization processes that could also explain the observed Martian remanent magnetic field. Assuming a cold early Mars, a cryosphere could trap such CH4 as clathrates in stable form at depth. The maximum storage capacity of such a clathrate cryosphere has been recently estimated to be 2 × 1019 to 2 × 1020 moles of methane. We estimate how large amounts of serpentinization‐derived CH4 stored in the cryosphere have been released into the atmosphere during the Noachian and the early Hesperian. Due to rapid clathrate dissociation and photochemical conversion of CH4 to H2, these episodes of massive CH4 release may have resulted in transient H2‐rich atmospheres, at typical levels of 10–20% in a background 1–2 bar CO2 atmosphere. The collision‐induced heating effect of H2 present in such an atmosphere has been shown to raise the surface temperature above the water freezing point. We show how local and rapid destabilization of the cryosphere can be induced by large events (such as the Hellas Basin or Tharsis bulge formation) and lead to such releases. Our results show that the early Mars cryosphere had a sufficient CH4 storage capacity to have maintained H2‐rich transient atmospheres during a total time period up to several million years or tens of million years, having potentially contributed to the formation of valley networks during the Noachian/early Hesperian.

Experimental investigation of a collision avoidance controller for a bimanual multi-fingered haptic interface

To present three-directional forces at ten human fingertips, we previously developed a bimanual multi-fingered haptic interface consisting of two five-fingered haptic hands and two interface arms. However, there is a risk that the component parts of the haptic interface will collide while an operator is manipulating the interface. A collision could be hazardous for the operator, and thus collision avoidance is essential. To solve this problem, we propose a collision avoidance controller for the bimanual multi-fingered haptic interface. The proposed controller prevents collisions while reducing the collision-induced effects on the haptic display. We carried out several experiments, the results of which show the validity of the proposed collision avoidance controller for the bimanual multi-fingered haptic interface.

Discharge and photo-luminance properties of a parallel plates electron emission lighting device

The gas discharge and photo-luminance properties of a planar lighting source featuring highly uniform light emission and mercury-free design were studied. The current density-voltage characteristics and the associated gas discharge of the devices operating with the values of the ratio of electric field to gas pressure (E/p) between 4.3 kV/Torr-cm and 35.7 kV/Torr-cm indicate that the width of the cathode fall extends over the entire gap between the two electrodes and the device is mostly in the obstructed discharge regime. The optical emission analysis confirmed the electron collision-induced gas emissions and strong effect of gas pressure on the phosphor emission when operated at constant current density, both are indicative of the primary roles played by the electron energy.

Collision-Induced Coherence Effect on Coherent Population Transfer

We investigate the effect of collision-induced coherence on coherent population transfer with the stimulated Raman adiabatic passage technique in a double A-type four-level system with a widely separated excited doublet. It is shown that when the two pulsed lasers with Rabi frequencies nearly comparable to the energy separation of the doublet are tuned to the particular frequency where the condition for quantum interference is satisfied, the very low transfer efficiency due to the nonadiabatic coupling between the two degenerate adiabatic states could be enhanced significantly with the increase of the collisional decay rates in a moderate range. The enhanced transfer efficiency results from the weakening of the nonadiabatic coupling between the two degenerate adiabatic states realized through collision-induced destructive quantum interference.

Control of the spontaneous emission spectrum in a driven N-type atom by dynamically induced quantum interference

The modification of the spontaneous emission spectrum has been studied in this paper in a four-level doubly driven N-type atomic system. In the presence of two coherent fields, emphasis has been given to studying the spectral distribution of spontaneous emission in the relaxation process of the initially prepared excited level. The phenomenon of quantum interference dynamically induced in the system by these fields can significantly change the spontaneous emission spectrum. We have shown the emergence of a two-peak spectrum where two widely separated symmetric peaks are associated with a sharp dark line at their mid-position. At different dynamic conditions, we have also shown that two symmetric peaks may appear in the spectrum with an extended dark zone between them. Depending on the values of the Rabi frequencies and the detunings of the external fields, one can achieve a large enhancement of very narrow spectral components within the spontaneous emission line shape under different conditions. The phenomenon of suppression of spectral line and the selective cancellation of spontaneous emission have also been discussed. The results shown in various cases are analysed by considering all possible dressed states corresponding to the bare state model. The influence of collision-induced effects on the spontaneous emission spectrum is investigated as a conditional case.

Polarizability response in polar solvents: Molecular-dynamics simulations of acetonitrile and chloroform

The relaxation of the many-body polarizability in liquid acetonitrile and chloroform at room temperature was studied by molecular-dynamics simulations. The collective polarizability induced by intermolecular interactions was included using first- and all-orders dipole-induced-dipole models and calculated considering both molecule-centered and distributed site polarizabilities. The anisotropic response was analyzed using a separation scheme that allows a decomposition of the total response in terms of orientational and collision-induced effects. We found the method effective in approximately separating the contributions of these relaxation mechanisms, although the orientational-collision-induced interference makes a non-negligible contribution to the total response. In both liquids the main contribution to the anisotropic response is due to orientational dynamics, but intermolecular collision-induced (or translational) effects are important, especially at short times. We found that higher-order interaction-induced effects were essentially negligible for both liquids. Larger differences were found between the center-center and site-site models, with the latter showing faster polarizability relaxation and better agreement with experiment. Isotropic and anisotropic spectra were computed from the corresponding time correlation functions. The lowest-frequency contributions are largely suppressed in the isotropic spectra and their overall shape is similar to the purely collision-induced contribution to the anisotropic spectra, but with an amplitude which is smaller by a factor of approximately 5 in acetonitrile and approximately 3 in chloroform.

Two-soliton collisions in a near-integrable lattice system.

We examine collisions between identical solitons in a weakly perturbed Ablowitz-Ladik (AL) model, augmented by either onsite cubic nonlinearity (which corresponds to the Salerno model, and may be realized as an array of strongly overlapping nonlinear optical waveguides) or a quintic perturbation, or both. Complex dependences of the outcomes of the collisions on the initial phase difference between the solitons and location of the collision point are observed. Large changes of amplitudes and velocities of the colliding solitons are generated by weak perturbations, showing that the elasticity of soliton collisions in the AL model is fragile (for instance, the Salerno's perturbation with the relative strength of 0.08 can give rise to a change of the solitons' amplitudes by a factor exceeding 2). Exact and approximate conservation laws in the perturbed system are examined, with a conclusion that the small perturbations very weakly affect the norm and energy conservation, but completely destroy the conservation of the lattice momentum, which is explained by the absence of the translational symmetry in generic nonintegrable lattice models. Data collected for a very large number of collisions correlate with this conclusion. Asymmetry of the collisions (which is explained by the dependence on the location of the central point of the collision relative to the lattice, and on the phase difference between the solitons) is investigated too, showing that the nonintegrability-induced effects grow almost linearly with the perturbation strength. Different perturbations (cubic and quintic ones) produce virtually identical collision-induced effects, which makes it possible to compensate them, thus finding a special perturbed system with almost elastic soliton collisions.

Collision-induced effects on the dielectric properties of liquid dimethylsulfoxide

Collision-induced effects on the dielectric properties of liquid dimethylsulfoxide

Gas-phase reactions of bare and oxo-ligated actinide and lanthanide cations with pentamethylcyclopentadiene studied in a quadrupole ion trap mass spectrometer

Reactions of bare and oxo-ligated monopositive ions of uranium and thorium with 1,2,3,4,5-pentamethylcyclopentadiene, C 10H 16, (HCp ∗) were examined in a quadrupole ion trap (QIT) mass spectrometer. Representative lanthanide ions, Ln + and LnO +, and tantalum ions, Ta + and TaO +, were studied for comparison. The product branching ratios for both primary and secondary reactions of the actinide ions demonstrated gas-phase organoactinide chemistry that is quite disparate from organolanthanide chemistry under comparable conditions for this neutral reactant. Particularly revealing were product distributions for ThO + and UO +, which indicated chemical behavior similar to that of bare Sm +. We conclude that at least one valence electron at the metal center of the actinide oxide ions must remain chemically active. In the case of UO +, this provides evidence for the chemical engagement of the quasi-valence 5f electrons, which is in distinct contrast to the inert character of the 4f electrons of the lanthanides in both Ln + and LnO +. Mass-selective chemistry of two primary products, UC 10H 10 + and UC 9H 8 +, also showed behavior similar to that of Sm + and UO +, implying that there are two covalent organouranium bonds in these complex ions. In comparing the QIT results for the lanthanides with those from a low-pressure ion cyclotron resonance (ICR) mass spectrometry study [Organometallics 16 (1997) 3845], qualitative agreement was found, but significant quantitative differences were apparent. Based on results from collision-induced dissociation and effects of variations in bath gas pressure in the QIT, we conclude that the discrepancies arise from the very different pressure regimes in the ICR and QIT. Evidently, the QIT can be operated over a range of pressures that manifest effects of collisional cooling for some reactions. For the lowest pressure QIT experiments, the high degree of fragmentation is reminiscent of the ICR results. We propose that the QIT bath gas can essentially act as an inert “solvent,” which serves to mediate high-energy processes due to energy transfer from nascent hot intermediate products via energy-dissipating collisions.

Collision-Induced Effects on the Dielectric Properties of Liquid Dimethylsulfoxide

We present a molecular dynamics (MD) simulation study of the dielectric properties of liquid dimethyl sulfoxide that includes interaction-induced effects due to molecular polarizability using a perturbative scheme in which the induced dipoles are computed a posteriori from the MD trajectories generated without explicit inductive forces. Static and dynamical quantities of relevance to the dielectric characterization of the liquid are reported for both polarizable and nonpolarizable versions of the system's collective dipolar densities. Our analysis within this scheme indicates that the role of the interaction induced contributions is predominantly to renormalize the magnitude of the permanent dipole fluctuations, with marginal effects upon the system's dielectric relaxation in the rotational-diffusion, microwave region of the spectrum. At higher frequencies, however, where the dielectric absorption is dominated by fast intermolecular librational motions, the dynamical effects of the molecular polarizability are more pronounced. In the presence of interaction induced contributions, the location of the peak in the MD far infrared absorption coefficient is in much better agreement with recent spectroscopic measurements of the intermolecular dynamics of this liquid.

The femtosecond birefringence of CO2: from the high pressure gas to the liquid phase

The optical heterodyne detected (OHD) birefringence of CO2 gas in the reduced density range from ρ/ρc = 0.09–0.82 and in the room temperature liquid are reported. Each birefringent response is separated into an electronic, rotational diffusion and non-diffusive nuclear component. The CO2 rotational relaxation times in the gas phase scale inversely with density in accordance with extended diffusion models of rotational reorientation. The rotational diffusion component of CO2 liquid (τD = 0.34 ps) appears to obey Debye–Stokes–Einstein behavior. The non-diffusive nuclear responses of the vapor samples exhibit only very modest changes with density and closely resemble the response function of the classical linear free rotor. The dominant, but not exclusive, contribution to the decay of the Raman anisotropy of high-pressure CO2 gas is inertial motion. The spectral density of the non-diffusive nuclear response of liquid CO2 is broader and has higher frequency components than the corresponding gas-phase spectral densities, indicating the relative importance of interaction induced effects. The greater extent of collision-induced effects is clearly evident for CS2 liquid compared with liquid CO2 when the spectral densities of the non-diffusive nuclear responses of liquid CO2 and CS2 are compared as a function of reduced frequency. Inertial motion clearly makes a much larger contribution to the birefringence of liquid CO2 than to that of liquid CS2 (at room temperature). Copyright © 2000 John Wiley & Sons, Ltd.

The ultrafast optical Kerr effect in liquid fluoroform: an estimate of the collision-induced contribution

The ultrafast optical Kerr effect (OKE) of liquid fluoroform at 296 K and 125 bar has been measured with 25 fs pulses. Results are compared to those of chloroform which is structurally similar. The nuclear response in fluoroform is ca. 110 times weaker than in chloroform. Diffusive relaxation of the anisotropy with 0.80±0.10 ps time constant is assigned to rotational motion. The OKE spectral density is compared to the far-infrared spectra of liquid fluoroform with a power law which relates the corresponding relaxation functions. It follows that collision-induced effects account for 25–30% of the OKE spectral integral.

Nonresonant intermolecular spectroscopy beyond the Placzek approximation. II. Fifth-order spectroscopy

We present an instantaneous normal mode analysis of the fifth-order polarizability-weighted densities of states for CS2 for experimentally relevant polarization conditions. We illustrate that polarization selectivity can be used to enhance selectively different contributions to the fifth-order spectrum. We show that the fifth-order spectrum arises predominantly from collision-induced scattering and from cross terms between collision-induced effects and librations, with only a vanishingly small pure librational contribution. We also demonstrate that there is no direct relationship between the third- and fifth-order Raman-weighted densities of states.

Temporal and spatial evolution of collision-induced stimulated effects in alkali atoms

A computational study of the optical propagation of Stokes light in a collisionally broadened three-level V-system Raman amplifier is presented. The Stokes light consists of two distinct spectral components: off-resonance stimulated Raman scattering and on-resonance stimulated fluorescence. These two signals are induced by collisional transfer of population from the excited state to the state. The intensity dependence of these effects on the buffer gas and intensity and detuning of the exciting radiations is calculated. In the calculations the probe signals and spontaneous scatterings were used to induce the stimulated signals. We have carried out the calculations over physically realistic propagation distances. The theory was compared with our experimental work and the results of the numerical analysis are used to explain some events observed in the experiments in which the physical mechanism has not yet been understood.

Solvent dynamics derived from optical Kerr effect, dielectric dispersion, and time-resolved stokes shift measurements: an empirical comparison

Abstract Data from the optical Kerr effect, time-resolved Stokes shift, and dielectric dispersion experiments on 21 common room temperature solvents are collected and compared. The correlation functions of the collective variables (polarizability, solvation energy, and dipole moment fluctations) responsible for each observable are first extracted from the experimental data and compared directly. In any given solvent the decay times of these various correlation functions are often vastly different. Such differences mainly result from the fact that intermolecular correlations affect the collective variables sampled by each technique in a different manner. To compare dynamics at a more basic level, power law relations are applied in an attempt to account for these correlations and to examine the extent to which the collective dynamics in these three experiments can be viewed as arising from the same underlying single-particle motions (primarily rotations). The Stokes shift and dielectric correlation functions can be reasonably inter-related in this manner, but the polarizability anisotropy monitored with Kerr experiments cannot be as simply related to the former two dynamics, probably due to the importance of collision-induced effects in the latter case.

The collisional energy transfer between the D 1 Π and d 3 Π states of the NaK dimer induced by argon buffer gas

Π→X1Σ+ transitions and the continuum spectrum of d3Π→a3Σ+ transitions of the NaK dimer in a heat pipe could be observed in the range of 500–700 nm. The collision-induced enhancement effects of the intensities Id→a and the quenching effect of the intensities ID→X by collisions with argon buffer gas at different pressures were measured experimentally. Based on the stationary collisional model and lifetime measurements, the quenching cross sections and cross sections for collision-induced energy transfer between the D1Π and d3Π states could be estimated.