Experimental setup for Fourier transform infrared spectroscopy studies in condensed matter at high pressure and low temperatures

Bini, Roberto; Ballerini, R.; Pratesi, G.; Jodl, H. J.

doi:10.1063/1.1148261

Cited by 112 publications

(83 citation statements)

References 31 publications

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“…The fluorescence of a ruby chip 5 µm in diameter is used as a pressure gauge (28). The presence of ice VI in the SAC is checked by measuring the FTIR spectrum with a Bruker spectrometer IFS120 HR (29).…”

Section: Methodsmentioning

confidence: 99%

Melting dynamics of ice in the mesoscopic regime

Citroni

Fanetti

Falsini³

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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How does a crystal melt? How long does it take for melt nuclei to grow? The melting mechanisms have been addressed by several theoretical and experimental works, covering a subnanosecond time window with sample sizes of tens of nanometers and thus suitable to determine the onset of the process but unable to unveil the following dynamics. On the other hand, macroscopic observations of phase transitions, with millisecond or longer time resolution, account for processes occurring at surfaces and time limited by thermal contact with the environment. Here, we fill the gap between these two extremes, investigating the melting of ice in the entire mesoscopic regime. A bulk ice I h or ice VI sample is homogeneously heated by a picosecond infrared pulse, which delivers all of the energy necessary for complete melting. The evolution of melt/ice interfaces thereafter is monitored by Mie scattering with nanosecond resolution, for all of the time needed for the sample to reequilibrate. The growth of the liquid domains, over distances of micrometers, takes hundreds of nanoseconds, a time orders of magnitude larger than expected from simple H-bond dynamics.Mie scattering | temperature jump | superheating | laser heating | anvil cell M elting of ice is one of the most common occurrences on our planet, from polar ices to glaciers, to the morning frost and the preparation of our drinks. Ices are present as well in extraterrestrial environments, planetary and intersellar, going through extremely different pressure and temperature conditions, where many phase boundaries are encountered. The molecular mechanisms of melting and the characteristic timescales of the process are not well elucidated, as for any other phase transition. In fact, great effort is presently being made with state of the art experimental techniques to understand the intrinsic kinetics of structural transformations, particularly under dynamic compression, by which phase-transition boundaries up to extreme pressures (P) and temperatures (T) can be accessed (1-6). Melting is the least hindered of phase transitions, requiring the disruption of the crystalline order and the achievement of the local structure of the liquid phase.The dynamics of melting have been studied up to the present in the picosecond timescale, observing structural changes on a length scale of few nanometers, in the attempt to explain the fundamental mechanisms of the transition onset. In both simulations and experiments, micrometric-or submicrometric-sized crystals can be rapidly heated above the melting temperature (Tm ), into a superheated state where melting occurs. Metals and water ice have been the test systems. Simulations have revealed a nucleation and growth mechanism (7-11), and nucleation has been especially addressed, in trying to determine the minimum number of atoms/molecules needed to form a critical nucleus for the transitions, the solid/melt interfacial energy, the transient local structures achieved during the transformation, and the role of defects and surfaces. Experimentally...

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Section: Methodsmentioning

confidence: 99%

Melting dynamics of ice in the mesoscopic regime

Citroni

Fanetti

Falsini³

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…The high-pressure reactions were triggered by focusing the UV multiline emission of an Ar ion laser (350 nm) onto the sample with power ranging from 50 to 610 mW, taking care to homogeneously irradiate the whole sample. FTIR absorption measurements were performed with a Bruker-IFS 120 HR spectrometer modified for high-pressure measurements (40,41). The instrumental resolution was 1 cm Ϫ1 .…”

Section: Methodsmentioning

confidence: 99%

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

Ceppatelli¹,

Bini²,

Schettino³

2009

Proc. Natl. Acad. Sci. U.S.A.

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High-pressure methods have been demonstrated to be efficient in providing new routes for the synthesis of materials of technological interest. In several molecular compounds, the drastic pressure conditions required for spontaneous transformations have been lowered to the kilobar range by photoactivation of the reactions. At these pressures, the syntheses are accessible to large-volume applications and are of interest to bioscience, space, and environmental chemistry. Here, we show that the short-lived hydroxyl radicals, produced in the photodissociation of water molecules by near-UV radiation at room temperature and pressures of a few tenths of a gigapascal (GPa), can be successfully used to trigger chemical reactions in mixtures of water with carbon monoxide or nitrogen. The detection of molecular hydrogen among the reaction products is of particular relevance. Besides the implications in fundamental chemistry, the mild pressure and irradiation conditions, the efficiency of the process, and the nature of the reactant and product molecules suggest applications in synthesis.high-pressure chemistry ͉ photocatalysis T he application to molecular systems of suitable external pressures causes a density increase that determines a strengthening of the intermolecular interactions leading first to changes in the aggregation state of the material, and then to crystalline phase transitions (1). Upon further compression, the possible overlap of the electronic density of nearest-neighbor molecules can also trigger a complete reconstruction of the chemical bonds, giving rise to new materials in some cases recoverable at ambient conditions (2). After the pioneering work on the pressure-induced polymerization of cyanogen (3) and acetylene (4) crystals, several simple molecular crystals have been reported to react upon application of suitable external pressure, giving rise to high-quality polymeric (5-7) and amorphous (8-10) materials of potential technological interest. These transformations require pressures from several to 100 GPa, as in the nitrogen case (7), but the reaction threshold pressure has been successfully lowered in almost all of the unsaturated hydrocarbons studied so far by a photoactivation of the high-pressure reactions (11). In some cases, an increasing selectivity (5) or the opening of new reaction paths (12) is also observed. These syntheses are appealing because only physical methods are used, thus representing an interesting perspective for a green chemistry (13).The mechanisms governing the photoinduced reactivity of molecular systems derive from the structural and charge density distribution changes after an electronic transition. In general, the excited molecule is characterized by a reduced binding order that determines molecular bonds stretching, a lowering of rotational and torsional barriers, an increase in the polarity, and even dissociation and ionization. These species can be particularly aggressive from a chemical point of view and, depending on their lifetime and free mean path, can trigger a...

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“…The polycrystalline samples were mounted onto a closed cycle He cryostat and coupled into the sample compartment of the FTIR with cassegrain optics as previously described. 43 Only intense isolated bands with high Lorentzian character (> 85%) were analyzed. Bruker's OPUS software was used to fit a sum of Lorentzian bands 44 to the IR lineshapes as described elsewhere.…”

Section: Computational Detailsmentioning

confidence: 99%

Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Schatschneider

Liang²,

Jezowski

et al. 2012

CrystEngComm

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Prediction of the relative stabilities and phase transition behavior of molecular crystalline polymorphs is highly coveted as distinct phases can possess different physical and chemical properties while having similar energies. Crystalline tetracyanoethylene (TCNE, C 6 N 4 ) is known to exhibit rich solid state phase behavior under different thermodynamic conditions, as demonstrated by a wealth of experimental studies on this system. Despite this fact, the role of temperature and kinetics on the phase diagram of TCNE remains poorly understood. Here, first-principles calculations and highresolution Fourier-transformed infrared (HR-FTIR) spectroscopy experiments are used to study the relative stabilities of the cubic and monoclinic phases of TCNE as a function of temperature. Specifically, density-functional theory with the van der Waals interactions method of Tkatchenko and Scheffler (DFT+vdW) is employed. The accuracy of this approach is demonstrated by the excellent agreement between the calculated and experimental structures. We find that the cubic phase is the most stable polymorph at 0 K, but becomes less favorable than the monoclinic phase at 160 K. This temperature-induced phase transition is explained on the basis of varying close contacts and vibrational entropies as a function of temperature. These findings are supported by a temperaturedependent HR-FTIR linewidth study of the CMN vibrons.

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Experimental setup for Fourier transform infrared spectroscopy studies in condensed matter at high pressure and low temperatures

Cited by 112 publications

References 31 publications

Melting dynamics of ice in the mesoscopic regime

Melting dynamics of ice in the mesoscopic regime

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

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