Perpendicular Transition Research Articles

Horizontal to perpendicular transition of lamellar and cylinder phases in block copolymer films induced by interface segregation of single-chain nanoparticles during solvent evaporation.

How to fabricate perpendicularly oriented domains (PODs) of lamellar and cylinder phases in block copolymer thin films remains a major challenge. In this work, via a coarse-grained molecular dynamics simulation study, we report a solvent evaporation strategy starting from a mixed solution of A-b-B-type diblock copolymers (DBCs) and single-chain nanoparticles (SCNPs) with the same composition, which is capable of spontaneously generating PODs in drying DBC films induced by the interface segregation of SCNPs. The latter occurs at both the free surface and substrate and, consequently, neutralizes the interface selectivity of distinct blocks in DBCs, leading to spontaneous formation of PODs at both interfaces. The interface segregation of SCNPs is related to the weak solvophilicity of the internal cross-linker units. A mean-field theory calculation demonstrates that the increase in the chemical potential of SCNPs in the bulk region drives their interface segregation along with solvent evaporation. We believe that such a strategy can be useful in regulating the PODs of DBC films in practical applications.

Direct observation of the ledge-typed twin boundary in a martensitic steel

The structure at the {112} twin boundaries in martensitic steels has been extensively debated recently. On the one hand, it was claimed to be the omega phase, similar to Ti alloys. On the other hand, it was considered artifacts induced by the double diffraction effect from the overlaps of twin-matrix crystals at their boundaries. In this study, we clarify the twin structure in a martensitic steel providing a detailed investigation of the α′ martensite twin boundaries using experiment and simulation. The fundamental for rejecting the existence of the omega phase in steels is based on the atomic resolution imaging from the <111> direction of twin structure, which was so far challenged to be acquired for such nano-sized twinned systems. The obtained result confirms the ledge-typed twin boundary that causes the visually omega-like forms when observed from other zone axes. The ledges occurred on {110} planes, making them secondary twin planes with coherent characteristics. Furthermore, these ledges were found to transit in a gradual manner from the primary (112) twin plane to (011) and then to (1¯10) secondary twin planes; a perpendicular transition from (112) to (1¯10) was not observed. Such a transitional behavior was explained in view of lowering total twin boundary energy, evaluated by the theoretical prediction of system energy and the geometric phase analysis of the twin planes. Double diffraction and rotational Moiré effects clarified the extra spots in the diffraction pattern obtained at the twin-matrix overlapped regions. This study gives light of understanding twinning in the bcc crystals.

Manipulating Parallel and Perpendicular Multiphoton Transitions in H2 Molecules

We demonstrate that dissociative ionization of H_{2} can be fully manipulated in an angle-time-resolved fashion, employing a polarization-skewed (PS) laser pulse in which the polarization vector rotates. The leading and falling edges of the PS laser pulse, characterized by unfolded field polarization, trigger, sequentially, parallel and perpendicular transitions of stretching H_{2} molecules, respectively. These transitions result in counterintuitive proton ejections that deviate significantly from the laser polarization directions. Our findings demonstrate that the reaction pathways can be controlled through fine-tuning the time-dependent polarization of the PS laser pulse. The experimental results are well reproduced using an intuitive wave-packet surface propagation simulation method. This research highlights the potential of PS laser pulses as powerful tweezers to resolve and manipulate complex laser-molecule interactions.

High-Resolution Laser Spectroscopy of a Functionalized Aromatic Molecule.

We present a high-resolution laser spectroscopic study of the Ã2B2-X̃2A1 and B̃2B1-X̃2A1 transitions of calcium(I) phenoxide, CaOPh (CaOC6H5). The rotationally resolved band systems are analyzed using an effective Hamiltonian model and are accurately modeled as independent perpendicular (b- or c-type) transitions. The structure of calcium monophenoxide is compared to previously observed Ca-containing radicals, and implications for direct laser cooling are discussed. This work demonstrates that functionalization of aromatic molecules with optical cycling centers can preserve many of the properties needed for laser-based control.

Dual-Band Dual-Polarization Horn Antenna Array Based on Orthomode Transducers With High Isolation for Satellite Communication

A dual-band dual-polarization horn antenna array is proposed for Ku-band satellite communication (SATCOM) in this article. A miniaturized orthomode transducer (OMT) using the mutually perpendicular multistep waveguide transition and coupled transition to transmit TE10 mode and TE01 mode, respectively, is integrated into the radiation element. The high isolation characteristic of horizontal polarization in the transmitting band (Tx) and vertical polarization in the receiving band (Rx) desired for SATCOM is realized. Moreover, the sinusoid-tapered horn antenna and the radiating cross-shaped cavity are employed as the shared-aperture element to radiate orthogonal waves simultaneously, having the potential of wide bandwidth, low sidelobes, and high radiation efficiency. With the facility of the 3-D metal printing technology, a horn antenna array consisting of the proposed 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times4$ </tex-math></inline-formula> radiation elements and feeding networks is demonstrated and fabricated. The gains up to 26.48 and 26.51 dBi with radiation efficiencies of around 94% and 90% are obtained at Tx- and Rx-bands, respectively. Benefitted from the advantages of compact size, high gain, and high efficiency, the proposed horn antenna array is suitable to tackle the high-throughput demand in Ku-band SATCOM systems.

Synthesis, structure investigation, DFT analysis, optical, and photoelectrical properties of 9-bromo-3-hydroxychromeno[4,3-b]pyrazolo[4,3-e]pyridin-5(1H)-one (BHCPP)

Chemical transformation of 6-bromochromone-3-carbonitrile (1) with cyanoacetohydrazide in boiling acetic acid yielded the novel 9-bromo-3 hydroxychromeno[4,3-b]pyrazolo[4,3-e]pyridin-5(1H)-one (2, BHCPP). At the B3LYP/6–311++G (d, p) level, Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) were utilized to investigate optimal geometry, natural bond orbital (NBO) analyses, FT-IR spectroscopic data, frontier molecular orbitals (FMOs), perpendicular electronic transition states, and NLO characteristics. The calculated total energy and thermodynamic characteristics at the same level of calculations confirmed the higher stability of the suggested structure (BHCPP) as compared with other predictable products (C, D and 3). DFT computed results and the associated experimental data were found to be in good agreement. The alpha pyrone derivative (BHCPP) was discovered to be the most stable structure in both the gaseous and solution states using PCM. The calculated total energies of all expected products are increase in solution, indicating solvent stabilizes all predicted products. Based on the experimental and theoretical results, the synthetic pathway for the formation of compound 3 was excluded, while compounds C and D considered as intermediates throughout the preparation of the more stable product 2 (BHCPP). The global reactivity descriptors were calculated using the energy of FMOs, indicating the molecule is chemically hard with increased kinetic stability and electron donating capabilities. The antimicrobial investigation was examined for the prepared compound (BHCPP).

Impact of renal chimney intra-aortic stent length on branch and end-stent angle in chimney endovascular aneurysm repair and endovascular aneurysm sealing configurations.

Practice patterns and durability of parallel stent graft techniques in complex endovascular aneurysm repair (EVAR) remain poorly defined. We aimed to quantify and compare the impact of renal chimney intra-aortic stent length (IASL) on geometric deformations of renal arteries in complex EVAR. Thirty-eight nonconsecutive patients underwent EVAR utilizing parallel stent graft techniques (chimney EVAR [chEVAR], n = 28; chimney endovascular aneurysm sealing [chEVAS], n = 10) between 2010 and 2016. A total of 59 renal chimney stent grafts were used. Geometric quantification was derived from three-dimensional model-based centerline extraction. Renal chimney intra-aortic stent length (IASL) was defined as the length of chimney stent that extended from the proximal edge of the chimney stent to the ostium of the corresponding renal artery. Mean IASL for both left and right renal arteries in the cohort was 35.7mm. Renal arteries containing chimney IASL <30mm trended toward a greater branch angle (135.4 vs. 127.8°, p = .06). Left renal arteries showed significantly greater branch angle among those with IASL <40mm (135.5 vs. 121.7°, p = .045). Mean IASL for renal arteries in chEVAR was significantly longer compared to chEVAS (39.2 vs. 26.3mm, p = .003). No difference was noted in overall branch angle or end-stent angle based on procedure type. ChEVAR with IASL <30mm had significantly greater end-stent angle (48.2 vs. 33.5°, p = .03). In contrast, chEVAS patients showed no difference in end-stent angle based on IASL thresholds, but did have significantly greater branch angle among those with IASL <30mm when grouped by both all renal arteries (133.5 vs. 113.5°, p = .004) and right renal arteries (134.3 vs. 111.6°, p = .02). Renal chimney stents with longer IASL appear to exhibit less renal artery deformation, suggesting a more gradual and perpendicular transition of the chimney stent across the renal ostium.

New Photoelectron-Valence Electron Interactions Evident in the Photoelectron Spectrum of Gd2O.

Evidence of strong photoelectron-valence electron (PEVE) interactions has been observed in the anion photoelectron (PE) spectra of several lanthanide suboxide clusters, which are exceptionally complex from an electronic structure standpoint and are strongly correlated systems. The PE spectrum of Gd2O-, which should have relatively simple electronic structure because of its half-filled 4f subshell, exhibits numerous electronic transitions. The electron affinity determined from the spectrum is 0.26 eV. The intensities of transitions to excited states increase relative to the lower-energy states with lower photon energy, which is consistent with shakeup transitions driven by time-dependent electron-neutral interactions. A group of intense spectral features that lie between electron binding energies of 0.7 and 2.3 eV are assigned to transitions involving detachment of an electron from outer-valence σu and σg orbitals that have large Gd 6s contributions. The spectra show parallel transition manifolds in general, which is consistent with detachment from these orbitals. However, several distinct perpendicular transitions are observed adjacent to several of the vertical transitions. A possible explanation invoking interaction between the ejected electron and the high-spin neutral is proposed. Specifically, the angular momentum of electrons ejected from σu or σg orbitals, which is = 1, can switch to = 0, 2 with an associated change in the Ms of the remnant neutral, which is spin-orbit coupling between a free electron and the spin of a neutral.

Rovibrational spectroscopy of the CH+-He and CH+-He4 complexes

A cryogenic 22-pole ion trap apparatus is used in combination with a table-top pulsed IR source to probe weakly bound CH+-Heand CH+-He4 complexes by predissociation spectroscopy at 4 K. The infrared photodissociation spectra of the C–H stretching vibrations are recorded in the range of 2720–2800 cm−1. The spectrum of CH+-Heexhibits perpendicular transitions of a near prolate top with a band origin at 2745.9 cm−1, and thus confirms it to have a T-shaped structure. For CH+-He4, the C-H stretch along the symmetry axis of this oblate top results in parallel transitions.

Surface circular-arc defects interacted by laser-generated Rayleigh wave

In this work, the finite element method (FEM) is used to investigate the propagation of laser-generated Rayleigh wave along the material surface at the quarter-arc transition surface under the thermoelastic regime, and to establish the relationship between the circular-arc radius and the time domain characteristics of reflected and transmitted Rayleigh waves. The simulation shows that the amplitude of the reflected Rayleigh wave decreases whereas the amplitude of the transmitted Rayleigh wave increases as the radius increases, which is significantly different from the well-studied interaction of Rayleigh waves with the perpendicular transition surface. By introducing the circular-arc defects which are easily formed in some engineering components during the material surface quenching, we find that the depth gauging of the surface circular-arc defects is more accurate in comparison to the surface rectangular defects based on the arrival time of the transmitted Rayleigh wave. This is further verified by the corresponding experimental results. These foundings are of practical values for detecting the depth of the arc defect quantitatively by the laser ultrasonic technique.

X-ray magnetic linear dichroism as a probe for non-collinear magnetic state in ferrimagnetic single layer exchange bias systems

Ferrimagnetic alloys are extensively studied for their unique magnetic properties leading to possible applications in perpendicular magnetic recording, due to their deterministic ultrafast switching and heat assisted magnetic recording capabilities. On a prototype ferrimagnetic alloy we demonstrate fascinating properties that occur close to a critical temperature where the magnetization is vanishing, just as in an antiferromagnet. From the X-ray magnetic circular dichroism measurements, an anomalous ‘wing shape’ hysteresis loop is observed slightly above the compensation temperature. This bears the characteristics of an intrinsic exchange bias effect, referred to as atomic exchange bias. We further exploit the X-ray magnetic linear dichroism (XMLD) contrast for probing non-collinear states which allows us to discriminate between two main reversal mechanisms, namely perpendicular domain wall formation versus spin-flop transition. Ultimately, we analyze the elemental magnetic moments for the surface and the bulk parts, separately, which allows to identify in the phase diagram the temperature window where this effect takes place. Moreover, we suggests that this effect is a general phenomenon in ferrimagnetic thin films which may also contribute to the understanding of the mechanism behind the all optical switching effect.

Dissociative photoionization of NO across a shape resonance in the XUV range using circularly polarized synchrotron radiation.

We report benchmark results for dissociative photoionization (DPI) spectroscopy and dynamics of the NO molecule in the region of the σ* shape resonance in the ionization leading to the NO+(c3Π) ionic state. The experimental study combines well characterized extreme ultraviolet (XUV) circularly polarized synchrotron radiation, delivered at the DESIRS beamline (SOLEIL), with ion-electron coincidence 3D momentum spectroscopy. The measured (N+, e) kinetic energy correlation diagrams reported at four discrete photon energies in the extended 23-33 eV energy range allow for resolving the different active DPI reactions and underline the importance of spectrally resolved studies using synchrotron radiation in the context of time-resolved studies where photoionization is induced by broadband XUV attosecond pulses. In the dominant DPI reaction which leads to the NO+(c3Π) ionic state, photoionization dynamics across the σ* shape resonance are probed by molecular frame photoelectron angular distributions where the parallel and perpendicular transitions are highlighted, as well as the circular dichroism CDAD(θe) in the molecular frame. The latter also constitute benchmark references for molecular polarimetry. The measured dynamical parameters are well described by multichannel Schwinger configuration interaction calculations. Similar results are obtained for the DPI spectroscopy of highly excited NO+ electronic states populated in the explored XUV photon energy range.

Stereodynamic Imaging of Bromine Atomic Photofragments Eliminated from 1-Bromo-2-methylbutane Oriented via Hexapole State Selector.

Both single-laser and two-laser experiments were conducted to look into the ion-imaging of Br*(2P1/2) and Br(2P3/2) photofragmented from 1-bromo-2-methylbutane in the range 232-240 nm via a detection scheme of (2+1) resonance-enhanced multiphoton ionization. The angular analysis of these photofragment distributions yields the anisotropy parameter β = 1.88 ± 0.06 for the Br* excited state which arises from a parallel transition, while β = 0.63 ± 0.09 for the Br ground state indicates the contribution from both a perpendicular transition and a non-adiabatic transition. When a hexapole coupled with an orienting field was implemented, the parent molecules are spatially oriented to yield an orientation efficiency |⟨cosθ⟩| of 0.15. Besides the χ angle between the recoil velocity v and the transition dipole moment μ, orienting molecules allows for the evaluation of the angle α between v and the permanent molecular dipole moment d. The angular analysis of Br* photofragment distribution yields χ = 11.5° and α in the range from 160° to 180° with weak dependency. In the two-laser experiments, the angular anisotropy of Br photofragment distribution was found to be smaller (0.38 ± 0.10) when the photolysis wavelength was red-shifted to 240 nm, suggesting the increasing contributions from perpendicular transitions.

A high-level theoretical characterization of the electronic states and spectroscopic parameters of SrBr2+ and SrI2+, and thermodynamic stability in the family of strontium monohalides dications

Abstract The manifold of low-lying electronic states of the diatomic dications SrBr2+ and SrI2+ was investigated for the first time at a high level of theoretical treatment, SA-CASSCF/MRCI. A global picture of the potential energy curves of the Λ + S and Ω states, and the associated spectroscopic parameters provide reliable quantitative results attesting the thermodynamic stability of both species. Transition probabilities were computed for perpendicular and parallel transitions, and the corresponding radiative lifetimes evaluated. Trends in energetics and molecular properties are discussed for the series SrX2+ (X = F, Cl, Br, I) and CaX2+ (X = Br, I), and BaI2+.

Photodissociation by Circularly Polarized Light Yields Photofragment Alignment in Ozone Arising Solely from Vibronic Interactions.

We present a direct determination of photofragment alignment produced by circularly polarized light in photolysis of a planar polyatomic molecule. This alignment arises via a new mechanism involving coherent excitation of two mutually perpendicular in-plane transition dipole moment components. The alignment is described by a new anisotropy parameter γ_{2}^{'} that was isolated by a unique laser polarization geometry. The determination of the parameter γ_{2}^{'} was realized in ozone photolysis at 266nm where dc slice images of O(^{1}D_{2}) atomic fragments were acquired. A model developed for interpretation of the photolysis mechanism shows that it can exist only in case of failure of the Born-Oppenheimer approximation when electronic and vibrational (vibronic) interactions have to be taken into account. This finding suggests that determination of the alignment parameter γ_{2}^{'} can be used as a key for direct insight into vibronic interactions in photolysis of polyatomic molecules. The results obtained for ozone photolysis via the Hartley band showed significant γ_{2}^{'} alignment but little recoil speed dependence, consistent with the notion that, as opposed to the situation for derivative coupling, under our experimental conditions, the vibronic contributions to the nonadiabatic dynamics are not dependent on recoil speed.

Femtosecond predissociation dynamics of ethyl iodide in the B-band.

Femtosecond time-resolved velocity map ion imaging experiments are reported on the second absorption band (B-band) of ethyl iodide at 201.19 and 200.08 nm, corresponding to the 000 and 1810 transitions, i.e., the origin of the band and the first most intense vibronic state assigned to one quantum of excitation in the methyl torsion mode. Electronic predissociation lifetimes and the temporal evolution of the anisotropy have been determined by time-resolved resonance-enhanced multiphoton ionization of iodine and ethyl fragment images. A shorter lifetime measured at the origin of the band in comparison with methyl iodide indicates that predissociation in ethyl iodide is more favorable due to a stronger coupling between the initial Rydberg state and the valence repulsive state correlating with the dissociation fragments. Moreover, vibrational activity in the methyl torsion in the Rydberg state seems to enhance the probability of transfer of population to the valence repulsive state leading to a faster dissociation. The perpendicular character of the transition at early times and the loss of anisotropy as a function of time have been determined from the time-resolved angular distributions of the iodine and ethyl ion images. The initial anisotropy value is consistent with a purely perpendicular transition compatible with the excitation of the [6A'', 7A'] states with a minor parallel component to the C-I bond. The loss of initial anisotropy over time highlights the parent molecular rotation during predissociation and is compatible with a rotational temperature of the parent molecule of 100 K.

Communication: Substantial impact of the orientation of transition dipole moments on the dynamics of diatomics in laser fields

The formation of light-induced conical intersections (LICIs) between electronic states of diatomic molecules has been thoroughly investigated over the past decade. In the case of running laser waves, the rotational, vibrational, and electronic motions couple via the LICI giving rise to strong nonadiabatic phenomena. In contrast to natural conical intersections (CIs) which are given by nature and hard to manipulate, the characteristics of LICIs are easily modified by the parameters of the laser field. The internuclear position of the created LICI is determined by the laser energy, while the angular position is given by the orientation of the transition dipole moment (TDM) with respect to the molecular axis. In the present communication, using MgH+ as a showcase example, we exploit the strong impact of the orientation of the TDMs exerted on the light-induced nonadiabatic dynamics. Comparing the photodissociations induced by parallel or perpendicular transitions, a clear signature of the created LICIs is revealed in the angular distribution of the photofragments.

High resolution synchrotron radiation Fourier transform infrared spectrum of the COH-bending mode in methanol-D1 (CH2DOH)

In this work the high resolution synchrotron radiation Fourier transform spectrum in the range 1180–1300cm−1 corresponding to the COH-bending vibrational mode has been recorded and analyzed. The spectrum shows a structure analogous to a parallel band. Since the COH bending motion is one of the main contributors to the asymmetry in the torsional hindering potential barrier, the torsional barrier height in the excited state is expected to be quite different from that of the ground state. This makes the spectrum to spread over a wide region. Although the spectrum corresponding to the P- and R-branch looks very complicated, the Q-branches are well resolved and can be identified without much difficulty. It was possible to assign the spectra for K=0 to 10 for the trans- (e0) species. The interesting feature of the spectra is the absence of the lines for two other lower lying gauche symmetry species e1 and o1. The spectra due to any perpendicular transitions were absent as well. However some weak c-type transitions from gauche states (o1 and e1) in the ground state to the trans-species (e0) in the COD bending mode for low K-values ΔK=0 have been seen to be present in the spectra. These along with similar transitions for the OCD vibrational band are under investigation and the results will be communicated elsewhere. In the present work, analysis of the spectrum has been carried out to obtain precise term values and molecular parameters in the excited COH-bending state for the trans-species. The results will be shown valuable to assign similar spectra for the methanol-D2. This work represents the first reported high resolution study of this illusive vibrational mode in methanol-D1.

Stereodirectional images of molecules oriented by a variable-voltage hexapolar field: Fragmentation channels of 2-bromobutane electronically excited at two photolysis wavelengths.

The asymmetric-top molecule 2-bromobutane is oriented by means of a hexapole state selector; the angular distribution of the bromine atom photofragment, for the two fine-structure components, is acquired by velocity-map ion imaging. The molecular beam, spatially oriented along the time-of-flight axis, is intersected with a linearly polarized laser, whose polarization is tilted by 45° with respect to the detector surface. To obtain the mixing ratio of the perpendicular and parallel transitions, the fragment ion images and angular distributions can be appropriately simulated to give insight on the population mechanism of the specific electronic state involved at each selected excitation wavelength. The photofragment images obtained at 238.6 nm yielded an asymmetry factor β1 of 0.67, indicative of the extent of molecular orientation, and an anisotropy parameter β2 of 1.03, which is a signature of a prevailing parallel transition along the C-Br axis. When the photolysis wavelength is tuned to 254.1 nm, the corresponding angular distribution is less asymmetric (β1 = 0.24) and the obtained small value β2 = 0.12 is a characteristic of a predominantly perpendicular transition. The photofragment angular distributions are also affected by hexapole voltage, especially regarding the asymmetry factor, and this aspect provides information on the effect of molecular orientation.

Observation of the C2H radical using (1 + 2) REMPI via the [formula omitted] transition

We report the detection of the ethynyl (C2H) radical by (1+2) REMPI on the B̃2A′(T,Ka=0,1,2)←X̃2Σ+(0,31,0) transition. One parallel, B̃2A′(T,Ka=1)←X̃2Σ+(0,31,0) with EeV=37,946cm-1, and two perpendicular transitions, B̃2A′(T,Ka=0)←X̃2Σ+(0,31,0) with EeV=37,927cm-1 and B̃2A′(T,Ka=2)←X̃2Σ+(0,31,0) with EeV=38,002cm-1, are observed. The C2H radical was generated by the photodissociation of C2H2 at 193nm. By employing REMPI spectroscopy, we also studied the collisional induced rotational relaxation of C2H and measured rotational relaxation rate constants for this radical. The measured rotational relaxation rate constants for several values of J″ are (0.08–0.26)×10-9cm3molec-1s-1 and (0.75–1.92)×10-9cm3molec-1s-1 for nitrogen buffer gas and acetylene, respectively.