Resonant ion-pair formation in electron recombination with HF^+

The cross section for resonant ion-pair formation in the collision of low-energy electrons with HF^+ is calculated by the solution of the time-dependent Schrodinger equation with multiple coupled states using a wave packet method. A diabatization procedure is proposed to obtain the electronic couplings between quasidiabatic potentials of ^1Sigma^+ symmetry for HF. By including these couplings between the neutral states, the cross section for ion-pair formation increases with about two orders of magnitude compared with the cross section for direct dissociation. Qualitative agreement with the measured cross section is obtained. The oscillations in the calculated cross section are analyzed. The cross section for ion-pair formation in electron recombination with DF^+ is calculated to determine the effect of isotopic substitution.Comment: 12 pages, 12 figure

IR AND X-RAY PHOTOELECTRON SPECTROSCOPY OF V 2 O 5 , TiO 2 AND V/Ti-OXIDE SOL-GEL DERIVED FILMS INFRARDE^A IN RENTGENSKA FOTOELEKTRONSKA SPEKTROSKOPIJA V 2 O 5 , TiO 2 IN V/Ti-OKSIDNIH SOL-GEL FILMOV

Prejem rokopisa -received: 1998-12-06; sprejem za objavo -accepted for publication: 1998-12-14 V/Ti-oxide films were prepared by dip-coating from sols made by mixing of V-oxoisopropoxide and Ti-propoxide in V:Ti molar ratio in precursors 3:1, 1:1 and 1:3. Amorphous films were obtained after annealing at 300°C (1 h). IR spectroscopic analysis revealed that V=O stretching modes appeared at 1020 cm -1 in the IR spectrum of powder (V:Ti=1:1). However, in the IR spectra of a film with the same molar ratio the bands at 1008 and 914 cm -1 appeared suggesting the presence of V 4+ -O bonds. The new band at 790 cm -1 signalled the V-O-Ti bridging bonds connecting V-O and Ti-O polyhedra. XPS measurements confirmed that initial-state films contained V 5+ , V 4+ and Ti 4+ species, but at the film surface only V 5+ species existed. Sequential depth analysis of films performed with Ar + sputtering showed that the vanadium is reduced to 3+ oxidation state with progressive exposure while titanium is not affected. Key words: electrochromic (EC) devices, oxide films, IR spectroscopy, XPS, oxidation states, sputtering, sol-gel V/Ti-oksidne filme smo pripravili iz koloidnih raztopin V-oksoizopropoksida in Ti-propoksida v 2-propanolu s tehniko potapljanja. Molska razmerja V:Ti v prekurzorjih so zna{ala 3:1, 1:1 in 1:3. Amorfni filmi so nastali po segrevanju na 300°C (1h). V IR spektru pra{kastega vzorca (V:Ti = 1:1) so se valen~na nihanja V=O pojavila pri 1020 cm -1 . V IR spektru filma z istim molskim razmerjem pa se pojavita trakova pri 1008 c

Ab initio study of vibrational excitation of HF by low-energy electrons

Fixed-nuclei, static-exchange calculations have been performed to study the vibrational-rotational excitation of HF by electrons from threshold to 5 eV. Our calculated, R-dependent K-matrix elements in 2Σ+, 2Π, and 2Δ symmetry are combined with exact point-dipole and laboratory-frame first-Born-approximation results for higher symmetries to obtain converged, integrated cross sections. The calculations show strong threshold peaks which are related to the dependence of the 2Σ+ K-matrix elements on internuclear distance at small scattering energies

Повышение надежности вторичного источника питания постоянного тока резервированием сигналов обратной связи

The paper deals with the problem of improving the reliability of DC-DC power supplies with pulse-width modulation. The topicality of the work is related to the importance of power supply issues in modern electronics, since the quality of operation of consumer electrical appliances, including critical ones, directly depends on the serviceability of sources. The object of the study is feedback circuits aimed at stabilization of the parameters of power supply of consumers. Failures of the mentioned feedback circuits most often occurs due to the electronic components degradation under harsh operating conditions as well as under severe mechanical overloads. Such failures are dangerous for uncontrolled increase of power supply output voltage and output current. To avoid this, a new method of reserving voltage feedback signals is presented in the paper which is implemented on the basis of flyback supply topology. Feedback signals are formed from the optocoupler located on the load side and from the auxiliary winding of the power transformer, together forming two independent output voltage control circuits. Only one circuit performs stabilization at any given moment of time. If one of these circuits fails, the second one can simply replace it in its operation. The proposed method does not require any digital signal processing algorithms or microprocessor control modules and can be implemented on the basis of cheap, widely available analog chips that perform pulse-width control of the output voltage. As a result, the problem of sudden feedback loop failure is solved and the reliability of electrical equipment is increased. The validity of the proposed method is confirmed by the results of computer simulation with the use of MatLab-Simulink environment. The obtained results can be used in design of fault-tolerant secondary power supplies that operate in harsh operating conditions.В статье рассматривается проблема повышения надежности импульсных источников вторичного электропитания постоянного тока. Актуальность работы связана со значимостью электропитания в современной электронной технике, поскольку от исправности источников напрямую зависит качество работы электроприборов-потребителей, в том числе критически важных. Объектом исследования являются цепи обратной связи, осуществляющие стабилизацию параметров электропитания потребителей. Выход из строя указанных цепей чаще всего происходит из-за деградации электронных компонентов схемы в жестких условиях эксплуатации и при сильных механических перегрузках и опасен бесконтрольным увеличением выходного напряжения и тока источника. Чтобы этого избежать, авторами предложен способ резервирования сигналов обратной связи по напряжению, реализованный на базе источника, выполненного по обратноходовой топологии. Сигналы обратной связи формируются с оптрона, расположенного на стороне нагрузки, и с дополнительной обмотки силового трансформатора, вместе образуя два независимых контура регулирования выходного напряжения. В каждый момент времени стабилизацию осуществляет только один контур. При выходе из строя первого контура второй способен заменить его работу. Представленный способ не требует цифровой обработки сигналов и микропроцессорного управления и может быть реализован на базе доступных аналоговых микросхем, осуществляющих широтно-импульсное регулирование выходного напряжения источника. В результате решается проблема аварийного отказа цепей обратной связи, повышается надежность работы электрооборудования. Правильность предлагаемого подхода подтверждена результатами имитационного компьютерного моделирования в программе MatLab-Simulink. Полученные результаты могут использоваться при проектировании отказоустойчивых вторичных источников электропитания для работы в жестких условиях эксплуатации

Scattering matrix approach to the dissociative recombination of HCO+ and N2H+

We present a theoretical study of the indirect dissociative recombination of linear polyatomic ions at low collisional energies. The approach is based on the computation of the scattering matrix just above the ionization threshold and enables the explicit determination of all diabatic electronic couplings responsible for dissociative recombination. In addition, we use the multi-channel quantum-defect theory to demonstrate the precision of the scattering matrix by reproducing accurately ab initio Rydberg state energies of the neutral molecule. We consider the molecular ions N2H+ and HCO+ as benchmark systems of astrophysical interest and improve former theoretical studies, which had repeatedly produced smaller cross sections than experimentally measured. Specifically, we demonstrate the crucial role of the previously overlooked stretching modes for linear polyatomic ions with large permanent dipole moment. The theoretical cross sections for both ions agree well with experimental data over a wide energy range. Finally, we consider the potential role of the HOC+ isomer in the experimental cross sections of HCO+ at energies below 10 meV