Search results for "Metastability"
showing 10 items of 262 documents
X-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2
2001
Iron(II) complexes exhibiting thermal spin-crossover may be converted from the1A1low-spin (LS) state to the5T2high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST) and from the LS to the HS state by irradiation with red light (reverse LIESST). The lifetime of the metastable LIESST states may be sufficiently long to enable an X-ray diffraction study. The lattice parameters of a single crystal of [Fe(mtz)6](BF4)2(mtz = methyltetrazole) (space groupP21/n) were measured between 300 and 10 K. While one Fe lattice site (A) of the crystal changes from the HS to the LS state near 78 K, the other site (B) remains in the LS state. Using the green lig…
On/Off Photoswitching in a Cyanide-Bridged {Fe2Co2} Magnetic Molecular Square
2013
International audience; A repeatable bidirectional paramagnetic ↔ diamagnetic photomagnetic effect has been observed in the cyanide-bridged Fe-Co square complex {[Fe{B(pz)(4)}(CN)(3)](2)[Co(bik)(2)](2)}(ClO(4))(2)*3H(2)O [B(pz)(4) = tetrapyrazolylborate, bik = bis(1-methylimidazol-2-yl)ketone]. Magnetic measurements and low-temperature single-crystal X-ray diffraction experiments have shown that a complete electron transfer from the diamagnetic Fe(II)-Co(III) state to the paramagnetic Fe(III)-Co(II) metastable state is induced by 808 nm laser light irradiation, whereas the diamagnetic state is recovered in an almost quantitative yield under irradiation at 532 nm.
X-ray study of the light-induced metastable state of a spin-crossover compound
2000
Iron(II) complexes exhibiting thermal spin crossover may be converted from the1A1low-spin (LS) state to the5T2high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST). The lifetime of the metastable LIESST state may be sufficiently long for X-ray diffraction study. The lattice parameters of a single crystal of [Fe(ptz)6](BF4)2(ptz = propyltetrazole) were measured between 300 and 10 K, while the crystal changed from the HS to the LS state near 135 K. Using the green light (514 nm) of an argon-ion laser, the crystal was quantitatively converted to the metastable LIESST state at 10 K; its lattice parameters were measured up to 50 K, at which poin…
Pressure-Induced Transformations in PrVO4 and SmVO4 and Isolation of High-Pressure Metastable Phases
2013
Zircon-type PrVO4 and SmVO4 have been studied by high-pressure Raman spectroscopy up to 17 GPa. The occurrence of phase transitions has been detected when compression exceeds 6 GPa. The transformations are not reversible. Raman spectra of the high-pressure phases show similarities with those expected for a monazite-type phase in PrVO4 and a scheelite-type phase in SmVO4.The high-pressure phases have been also synthesized using a large-volume press and recovered at ambient conditions. X-ray diffraction measurements of the metastable products recovered after decompression confirms the monazite (PrVO4) and scheelite (SmVO4) structures of the high-pressure phases. Based upon optical properties …
The LIESST state of [Fe(pic)3]Cl2.EtOH – the superstructure under continuous irradiation
2005
The superstructure recently discovered in [Fe(pic)3]Cl2.EtOH at temperatures inside the step region of the high-spin–low-spin transition curve sheds new light on the anomalous transition behaviour in spin crossover compounds. The structure of the metastable LIESST state of [Fe(pic)3]Cl2.EtOH at 10 K has been measured. The decay has been followed by X-ray diffraction using a CCD camera in order to detect reflections of the superstructure building up during the decay. No signal above the noise of the CCD camera was observed, so that even diffuse scattering could not be detected. This finding is in agreement with correlation lengths of pair correlations of molecules in the HS and LS states bei…
Cluster simulations of structural transformations in yellow arsenic
2001
Abstract Yellow arsenic (y-As) consists of tetrahedral As4 molecules that may be packed in some amorphous and crystalline structures. Like many other arsenic structures, y-As is metastable and undergoes irreversible transitions (polymerization) under irradiation. The process of y-As polymerization, which is observed experimentally, usually leads to the formation of amorphous arsenic (a-As) possessing a continuous random network structure. Our previous quantum chemical simulation for an eight-atom cluster model performed using semi-empirical CNDO/BW approach, combined with optimization technique of cyclic coordinate descent, have shown a formation of molecular dimers due to breaking of one b…
Hold design supports learning and transfer of climbing fluency
2014
Being a discipline with a broad range of genres, rock climbing is an activity where participants seek to generalize the skills they learn in different performance contexts. A training strategy for achieving skill transfer was explored in a group of experienced climbers. Specifically, we tested the effect of practising on three routes, each of the same difficulty, but where handholds supported opportunities for using either a single technical action or multiple actions. Transfer of climbing fluidity in terms of the geometric index of entropy (GIE) of the hip trajectory was then assessed. We expected that learning would be induced on the route where multiple actions were usable. Results revea…
Resonances in the electron impact excitation of metastable states of mercury
1984
Metastable excitation of mercury by electron impact is studied at energies up to the first ionisation potential using an energy selected electron beam with an energy spread of 50 meV FWHM. A great number of resonances is observed in the excitation function. Agreement is good on the whole with a recent relativisticR-matrix calculation and with a former analysis of resonances in the elastic cross section.
Metastable memristive lines for signal transmission and information processing applications
2016
Traditional studies of memristive devices have mainly focused on their applications in nonvolatile information storage and information processing. Here, we demonstrate that the third fundamental component of information technologies-the transfer of information-can also be employed with memristive devices. For this purpose, we introduce a metastable memristive circuit. Combining metastable memristive circuits into a line, one obtains an architecture capable of transferring a signal edge from one space location to another. We emphasize that the suggested metastable memristive lines employ only resistive circuit components. Moreover, their networks (for example, Y-connected lines) have an info…
Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids
1983
Metastable peaks have been used to study the fragmentation pathways of the methyl and trideuteriomethyl chloropropenoates and chloromethyl propenoate. The molecular ion peaks of the unsaturated esters are more intense than those of the saturated esters, α-Cleavage, [MOCH3]+, produces the base peak in almost all compounds, the relative abundances of the additional peaks being low for chloromethyl propenoate. The losses of H2O, CH3. and COOH. indicate the isomerization of some ionized chloro esters to the chlorinated 2-butenoic acid molecular ions. An intense loss of H2O observed for methyl 2-chloropropenoate indicates its most facile isomerization, [ester]+˙ → [acid]+˙, whereas the isomeriza…