A Complex Investigation of LATP Ceramic Stability and LATP+PVDF Composite Membrane Performance: The Effect of Solvent in Tape-Casting Fabrication.

Redox flow batteries (RFBs) are a prospective energy storage platform to mitigate the discrepancy between barely adjustable energy production and fluctuating demand. The energy density and affordability of RFBs can be improved significantly through the transition from aqueous systems to non-aqueous (NAq) due to their wider electrochemical stability window and better solubility of active species. However, the NAqRFBs suffer from a lack of effective membranes with high ionic conductivity (IC), selectivity (low permeability), and stability. Here, we for the first time thoroughly analyse the impact of tape-casting solvents (dimethylformamide-DMF; dimethylsulfoxide-DMSO; N-methyl-2-pyrrolidone-NMP) on the properties of the composite Li-conductive membrane (Li1.3Al0.3Ti1.7(PO4)3 filler within poly(vinylidene fluoride) binder-LATP+PVDF). We show that the prolonged exposure of LATP to the studied solvents causes slight morphological, elemental, and intrastructural changes, dropping ceramic's IC from 3.1 to 1.6-1.9 ∙ 10-4 S cm-1. Depending on the solvent, the final composite membranes exhibit IC of 1.1-1.7 ∙ 10-4 S cm-1 (comparable with solvent-treated ceramics) along with correlating permeability coefficients of 2.7-3.1 ∙ 10-7 cm2 min-1. We expect this study to complement the understanding of how the processes underlying the membrane fabrication impact its functional features and to stimulate further in-depth research of NAqRFB membranes.

Evaluation of the Efficiency of Photoelectrochemical Activity Enhancement for the Nanostructured LaFeO3 Photocathode by Surface Passivation and Co-Catalyst Deposition.

Perovskite-type lanthanum iron oxide, LaFeO3, is a promising photocathode material that can achieve water splitting under visible light. However, the performance of this photoelectrode material is limited by significant electron-hole recombination. In this work, we explore different strategies to optimize the activity of a nanostructured porous LaFeO3 film, which demonstrates enhanced photoelectrocatalytic activity due to the reduced diffusion length of the charge carriers. We found that surface passivation is not an efficient approach for enhancing the photoelectrochemical performance of LaFeO3, as it is sufficiently stable under photoelectrocatalytic conditions. Instead, the deposition of a Pt co-catalyst was shown to be essential for maximizing the photoelectrochemical activity both in hydrogen evolution and oxygen reduction reactions. Illumination-induced band edge unpinning was found to be a major challenge for the further development of LaFeO3 photocathodes for water-splitting applications.

Charge storage mechanisms of a π-d conjugated polymer for advanced alkali-ion battery anodes.

The demand for fast-charging metal-ion batteries underlines the importance of anodes that work at high currents with no risk of dendrite formation. NiBTA, a one-dimensional Ni-based polymer derived from benzenetetramine (BTA), is a recently proposed promising material for safe fast-charging batteries. However, its charge-discharge mechanisms remained unclear and controversial. Here we solve the controversies by providing the first rigorous study using a combination of advanced theoretical and experimental techniques, including operando and ex situ X-ray diffraction, operando Raman spectroscopy and ex situ X-ray absorption near-edge spectroscopy (XANES). In safe potential ranges (0.5-2.0 V vs. M+/M, M = Li, Na or K), NiBTA offers high capacities, fast charge-discharge kinetics, high cycling stability and compatibility with various cations (Li+, Na+, K+). In the Na- and K-based cells, fast bulk faradaic processes are manifested for partially reduced states. Atomistic simulations explain the fast kinetics by facile rotations and displacements of the macromolecules in the crystal, opening channels for fast ion insertion. The material undergoes distinct crystal structure rearrangements in the Li-, Na- and K-based systems, which explains different electrochemical features. At the molecular level, the charge storage mechanism involves reversible two-electron reduction of the repeating units accompanied by a change of the absorption bandgap. The reversible reduction involves filling of the orbitals localized at the ligand moieties. No reduction of NiBTA beyond two electrons per repeating unit is observed at potentials down to 0 V vs. M+/M.

Development of vanadium-based polyanion positive electrode active materials for high-voltage sodium-based batteries.

Polyanion compounds offer a playground for designing prospective electrode active materials for sodium-ion storage due to their structural diversity and chemical variety. Here, by combining a NaVPO4F composition and KTiOPO4-type framework via a low-temperature (e.g., 190 °C) ion-exchange synthesis approach, we develop a high-capacity and high-voltage positive electrode active material. When tested in a coin cell configuration in combination with a Na metal negative electrode and a NaPF6-based non-aqueous electrolyte solution, this cathode active material enables a discharge capacity of 136 mAh g-1 at 14.3 mA g-1 with an average cell discharge voltage of about 4.0 V. Furthermore, a specific discharge capacity of 123 mAh g-1 at 5.7 A g-1 is also reported for the same cell configuration. Through ex situ and operando structural characterizations, we also demonstrate that the reversible Na-ion storage at the positive electrode occurs mostly via a solid-solution de/insertion mechanism.

Formation and Evolution of H2C3O+• Radical Cations: A Computational and Matrix Isolation Study.

The family of isomeric H2C3O+• radical cations is of great interest for physical organic chemistry and chemistry occurring in extraterrestrial media. In this work, we have experimentally examined a unique synthetic route to the generation of H2C3O+• from the C2H2···CO intermolecular complex and also considered the relative stability and monomolecular transformations of the H2C3O+• isomers through high-level ab initio calculations. The structures, energetics, harmonic frequencies, hyperfine coupling constants, and isomerization pathways for several of the most important H2C3O+• isomers were calculated at the UCCSD(T) level of theory. The complementary FTIR and EPR studies in argon matrices at 5 K have demonstrated that the ionized C2H2···CO complex transforms into the E-HCCHCO+• isomer, and this latter species is supposed to be the key intermediate in further chemical transformations, providing a remarkable piece of evidence for kinetic control in low-temperature chemistry. Photolysis of this species at λ = 410-465 nm results in its transformation to the thermodynamically most stable H2CCCO+• isomer. Possible implications of the results and potentiality of the proposed synthetic strategy to the preparation of highly reactive organic radical cations are discussed.

α-TiPO4 as a Negative Electrode Material for Lithium-Ion Batteries.

To realize high-power performance, lithium-ion batteries require stable, environmentally benign, and economically viable noncarbonaceous anode materials capable of operating at high rates with low strain during charge-discharge. In this paper, we report the synthesis, crystal structure, and electrochemical properties of a new titanium-based member of the MPO4 phosphate series adopting the α-CrPO4 structure type. α-TiPO4 has been obtained by thermal decomposition of a novel hydrothermally prepared fluoride phosphate, NH4TiPO4F, at 600 °C under a hydrogen atmosphere. The crystal structure of α-TiPO4 is refined from powder X-ray diffraction data using a Rietveld method and verified by electron diffraction and high-resolution scanning transmission electron microscopy, whereas the chemical composition is confirmed by IR, energy-dispersive X-ray, electron paramagnetic resonance, and electron energy loss spectroscopies. Carbon-coated α-TiPO4/C demonstrates reversible electrochemical activity ascribed to the Ti3+/Ti2+ redox transition delivering 125 mAh g-1 specific capacity at C/10 in the 1.0-3.1 V versus Li+/Li potential range with an average potential of ∼1.5 V, exhibiting good rate capability and stable cycling with volume variation not exceeding 0.5%. Below 0.8 V, the material undergoes a conversion reaction, further revealing capacitive reversible electrochemical behavior with an average specific capacity of 270 mAh g-1 at 1C in the 0.7-2.9 V versus Li+/Li potential range. This work suggests a new synthesis route to metastable titanium-containing phosphates holding prospective to be used as negative electrode materials for metal-ion batteries.

The Misconception of Mg2+ Insertion into Prussian Blue Analogue Structures from Aqueous Solution.

Prussian blue analogues (PBAs) are commonly believed to reversibly insert divalent ions, such as calcium and magnesium, rendering them as perspective cathode materials for aqueous magnesium-ion batteries. In this study, the occurrence of Mg2+ insertion into nanosized PBA materials is shown to be a misconception and conclusive evidence is provided for the unfeasibility of this process for both cation-rich and cation-poor nickel, iron, and copper hexacyanoferrates. Based on structural, electrochemical, IR spectroscopy, and quartz crystal microbalance data, the charge compensation of PBA redox can be attributed to protons rather than to divalent ions in aqueous Mg2+ solution. The reversible insertion of protons involves complex lattice water rearrangements, whereas the presence of Mg2+ ion and Mg salt anion stabilizes the proton (de)insertion reaction through local pH effects and anion adsorption at the PBA surface. The obtained results draw attention to the design of proton-based batteries operating in environmentally benign aqueous solutions with low acidity.

Monoclinic α-Na2FePO4F with Strong Antisite Disorder and Enhanced Na+ Diffusion.

A new monoclinic α-polymorph of the Na2FePO4F fluoride-phosphate has been directly synthesized via a hydrothermal method for application in metal-ion batteries. The crystal structure of the as-prepared α-Na2FePO4F studied with powder X-ray and neutron diffraction (P21/c, a = 13.6753(10) Å, b = 5.2503(2) Å, c = 13.7202(8) Å, ß = 120.230(4)°) demonstrates strong antisite disorder between the Na and Fe atoms. As revealed with DFT-based calculations, α-Na2FePO4F has low migration barriers for Na+ along the main pathway parallel to the b axis, and an additional diffusion bypass allowing the Na+ cations to go around the Na/Fe antisite defects. These results corroborate with the extremely high experimental Na-ion diffusion coefficient of (1-5)·10-11 cm2·s-1, which is 2 orders of magnitude higher than that for the orthorhombic ß-polymorph ((5-10)·10-13 cm2·s-1). Being tested as a cathode material in Na- and Li-ion battery cells, monoclinic α-Na2FePO4F exhibits a reversible specific capacity of 90 and 80 mAh g-1, respectively.

Titanium-based potassium-ion battery positive electrode with extraordinarily high redox potential.

The rapid progress in mass-market applications of metal-ion batteries intensifies the development of economically feasible electrode materials based on earth-abundant elements. Here, we report on a record-breaking titanium-based positive electrode material, KTiPO4F, exhibiting a superior electrode potential of 3.6 V in a potassium-ion cell, which is extraordinarily high for titanium redox transitions. We hypothesize that such an unexpectedly major boost of the electrode potential benefits from the synergy of the cumulative inductive effect of two anions and charge/vacancy ordering. Carbon-coated electrode materials display no capacity fading when cycled at 5C rate for 100 cycles, which coupled with extremely low energy barriers for potassium-ion migration of 0.2 eV anticipates high-power applications. Our contribution shows that the titanium redox activity traditionally considered as "reducing" can be upshifted to near-4V electrode potentials thus providing a playground to design sustainable and cost-effective titanium-containing positive electrode materials with promising electrochemical characteristics.

Efficacy and Safety of a Fixed Combination of Cinnarizine 20 mg and Dimenhydrinate 40 mg vs Betahistine Dihydrochloride 16 mg in Patients with Peripheral Vestibular Vertigo: A Prospective, Multinational, Multicenter, Double-Blind, Randomized, Non-inferiority Clinical Trial.

BACKGROUND AND OBJECTIVE: Vertigo derived from peripheral vestibular disorders is quite frequently encountered in daily clinical practice and can be a severely disabling symptom associated with substantial impairment of health-related quality of life for the affected patients. Betahistine, a structural analogue of histamine and presumably the most widely prescribed anti-vertigo drug worldwide, has previously been shown to be an effective and safe treatment for these patients. The objective of the present study was to evaluate whether the fixed combination of cinnarizine and dimenhydrinate (Arlevert®) is non-inferior and thus a potentially useful alternative to betahistine dihydrochloride in the treatment of patients suffering from peripheral vestibular vertigo. METHODS: In this prospective, multicenter, double-blind, randomized, non-inferiority clinical trial, outpatients from 8 ENT clinics in Austria, Bulgaria, the Czech Republic and Russia were randomly assigned to receive three times daily one tablet of either the fixed combination cinnarizine 20 mg/dimenhydrinate 40 mg or betahistine dihydrochloride 16 mg for 4 weeks. Primary endpoint was the reduction of the mean vertigo score (MVS), a validated 12-item composite score defined as the mean of 6 vertigo symptoms (dystasia and walking unsteadiness, staggering, rotary sensation, tendency to fall, lift sensation, blackout) and 6 trigger factors for vertigo (change of position, bowing, getting up, driving by car/train, head movements, eye movement), after 4 weeks of therapy, as judged by the patient on a 5-point visual analogue scale (VAS). The non-inferiority margin was set to 0.3. Secondary outcomes included the patient's and investigator's judgment of global efficacy, the patient's rating of impairment of daily activities, and safety/tolerability of the treatments. RESULTS: Three hundred and six patients (mean age 53.5 years, approximately 60% female) were enrolled and randomized to the fixed combination cinnarizine/dimenhydrinate (n = 152) or betahistine (n = 154) groups; 297 patients completed the study and 294 (146 and 148, respectively) were valid for the per-protocol analysis, which was used for the non-inferiority analysis. Treatment with cinnarizine/dimenhydrinate led to a stronger reduction of the MVS [least squares mean (LSM)] after 4-week therapy (primary endpoint) in comparison to betahistine (0.395 vs 0.488; difference: - 0.093, 95% CI - 0.180; - 0.007, p = 0.035); since the upper limit of the two-sided 95% confidence interval was not only below the non-inferiority margin of 0.3, but also entirely below 0, superiority of the fixed combination could be demonstrated. The combination preparation was also more effective after 1 week of therapy and received more favorable patient's ratings on overall efficacy and impairment of daily activities. Both treatments were very well tolerated. Only 12 patients (3.92%) reported 13 non-serious adverse events; 2 cinnarizine/dimenhydrinate-treated patients discontinued the study prematurely due to adverse events as compared to 5 betahistine-treated patients. CONCLUSION: The fixed combination of cinnarizine 20 mg and dimenhydrinate 40 mg was found to be not only non-inferior, but superior to betahistine 16 mg in the improvement of peripheral vestibular vertigo. Furthermore, taking into account a good and slightly favorable safety profile, the present study provides evidence that the fixed-combination preparation is a potent and even superior alternative to betahistine in the treatment of vertigo related to peripheral vestibular disorders. STUDY REGISTRATION: EudraCT No. 2011-004025-27.

The HKrCCHCO2 complex: an ab initio and matrix-isolation study.

We report an experimental and theoretical study on new noble-gas hydride complex HKrCCHCO2, which is the first known complex of a krypton hydride with carbon dioxide. This species was prepared by the annealing-induced H + Kr + CCHCO2 reaction in a krypton matrix, the CCHCO2 complexes being produced by UV photolysis of propiolic acid (HCCCOOH). The H-Kr stretching mode of the HKrCCHCO2 complex at 1316 cm-1 is blue-shifted by 74 cm-1 from the most intense H-Kr stretching band of HKrCCH monomer. The observed blue shift indicates the stabilization of the H-Kr bond upon complexation, which is characteristic of complexes of noble-gas hydrides. This spectral shift is slightly larger than that of the HKrCCHC2H2 complex (+60 cm-1) and significantly larger than that of the HXeCCHCO2 complex (+32 and +6 cm-1). On the basis of comparison with ab initio computations at the MP2 and CCSD(T) levels of theory, the experimentally observed absorption is assigned to the quasi-parallel configuration of the HKrCCHCO2 complex. The calculated complexation-induced spectral shift of the H-Kr stretching band (60.4 or 72.7 cm-1 from the harmonic calculations at the MP2 and CCSD(T) levels, respectively) agrees well with the experimental value.

Photochemistry of the H2O/CO System Revisited: The HXeOH···CO Complex in a Xenon Matrix.

We report on the complex of a noble-gas hydride HXeOH with carbon monoxide. This species is prepared via the annealing-induced H + Xe + OH···CO reaction in a xenon matrix, the OH···CO complexes being produced by VUV photolysis of the H2O···CO complexes. The H-Xe stretching mode of the HXeOH···CO complex absorbs at 1590.3 cm-1 and it is blue-shifted by 12.7 cm-1 from the H-Xe stretching band of HXeOH monomer. The observed blue shift indicates the stabilization of the H-Xe bond upon complexation, which is characteristic of complexes of noble-gas hydrides. The HXeOH···CO species is the first complex of a noble-gas hydride with carbon monoxide and the second observed complex of HXeOH. On the basis of the MP2/aug-cc-pVTZ-PP calculations, the experimental complex is assigned to the structure, where the carbon atom of CO interacts with the oxygen atom of HXeOH.

Spectroscopic characterization of the complex of vinyl radical and carbon dioxide: Matrix isolation and ab initio study.

We report on the preparation and vibrational characterization of the C2H3⋯CO2 complex, the first example of a stable intermolecular complex involving vinyl radicals. This complex was prepared in Ar and Kr matrices using UV photolysis of propiolic acid (HC3OOH) and subsequent thermal mobilization of H atoms. This preparation procedure provides vinyl radicals formed exclusively as a complex with CO2, without the presence of either CO2 or C2H3 monomers. The absorption bands corresponding to the ν5(C2H3), ν7(C2H3), ν8(C2H3), ν2(CO2), and ν3(CO2) modes of the C2H3⋯CO2 complex were detected experimentally. The calculations at the UCCSD(T)/L2a level of theory predict two structures of the C2H3⋯CO2 complex with Cs and C1 symmetries and interaction energies of -1.92 and -5.19 kJ mol-1. The harmonic vibrational frequencies of these structures were calculated at the same level of theory. The structural assignment of the experimental species is not straightforward because of rather small complexation-induced shifts and matrix-site splitting of the bands (for both complex and monomers). We conclude that the C1 structure is the most probable candidate for the experimental C2H3⋯CO2 complex based on the significant splitting of the bending vibration of CO2 and on the energetic and structural considerations.

Conformational Switching of HOCO Radical: Selective Vibrational Excitation and Hydrogen-Atom Tunneling.

Conformers of carboxyl radical (HOCO) have been studied by IR spectroscopy in argon and nitrogen matrices. In an argon matrix, only the lower-energy conformer trans-HOCO is observed, whereas both cis and trans conformers are found for deuterated carboxyl radical DOCO. In a nitrogen matrix, both conformers of HOCO and DOCO isotopologues can be prepared, indicating strong stabilization of the higher-energy cis conformer by a nitrogen matrix. Selective vibrational excitation promotes the trans-to-cis and cis-to-trans conversions of DOCO in an argon matrix and HOCO and DOCO in a nitrogen matrix, which is the first conformational photoswitching of an open-shell species. In a nitrogen matrix, the cis-to-trans and trans-to-cis conversions of HOCO is also found upon broadband IR light of the spectrometer, and the ratio of the quantum yields of these processes is about 3.3. The photoswitching peculiarities are in agreement with the available theoretical energy barriers. The higher-energy cis conformer decays to the lower-energy trans conformer via hydrogen-atom tunneling through the torsional barrier, which is also a unique observation for an open-shell species. The tunneling mechanism of the cis-to-trans switching is supported by the low-temperature limit of the reaction rate and by the H/D kinetic isotope effect. Our results suggest a large difference in the H/D kinetic isotope effects in nitrogen and argon matrices (∼5 and >100, respectively). The stabilizing effect on cis-DOCO by a nitrogen matrix (by 2 orders of magnitude versus an argon matrix) is much smaller than that on cis-HOCO (estimated to be >104).

Experimental determination of the absolute infrared absorption intensities of formyl radical HCO.

Formyl radical HCO is an important reactive intermediate in combustion, atmospheric and extraterrestrial chemistry. Like in the case of other transients, the lack of knowledge of the absolute IR intensities limits the quantitative spectroscopic studies on this species. We report the first experimental determination of the absorption intensities for the fundamental vibrational bands of HCO. The measurements have been performed using matrix-isolation FTIR spectroscopy. Determination of the values was based on the repeated photodissociation and thermal recovery of the HCO radical using the known value of the absorption coefficient of CO. The experimentally determined values (93.2±6.0, 67.2±4.5, and 109.2±6.6kmmol-1 for the ν1, ν2, and ν3 modes, respectively) have been compared to the calculated IR intensities obtained by DFT and UCCSD(T) computations.

Effect of Noncovalent Interactions on Vibronic Transitions: An Experimental and Theoretical Study of the C2 H⋠⋠⋠CO2 Complex.

We report on the experimental and theoretical infrared spectrum of the C2 H⋅⋅⋅CO2 complex. This complex was prepared by UV photolysis of propiolic acid (HC3 OOH) in argon and krypton matrices. The experimental bands of C2 H in the C2 H⋅⋅⋅CO2 complex are blue-shifted from those of the C2 H monomer. The calculations on the C2 H⋅⋅⋅CO2 structures were performed at the RMP2/aug-cc-pVTZ level. The relative stability of the complex structures was evaluated by using the RCCSD(T)/aug-cc-pVQZ level. To simulate the spectrum of the C2 H⋅⋅⋅CO2 complex, we developed the theoretical approach used earlier for the C2 H monomer. Based on the calculations, the main experimental bands of the C2 H⋅⋅⋅CO2 complex are assigned to the most stable parallel structure. Almost all the strong bands predicted by theory (with intensities >30 km mol-1 ) are observed in the experiment. To our knowledge, it is the first study of the effect of noncovalent interactions on vibronic transitions and the first report on an intermolecular complex of the C2 H radical.

VUV photochemistry of the H2OCO complex in noble-gas matrices: formation of the OHCO complex and the HOCO radical.

Vacuum ultraviolet (VUV, 130-170 nm) photochemistry of the H2OCO complex is studied by matrix-isolation infrared spectroscopy. The H2OCO complexes in Ne, Ar, Kr, and Xe matrices are generated by ultraviolet (UV, 193 and 250 nm) photolysis of formic acid (HCOOH). VUV photolysis of the H2OCO complexes is found to lead to the formation of the OHCO radical-molecule complexes and trans-HOCO radicals. It is shown that the matrix material, local matrix morphology, and possibly the H2OCO complex geometry strongly affect the VUV photolysis pathways. The intrinsic reactivity of the matrix-isolated OHCO complex resulting in the formation of trans-HOCO is directly demonstrated for the first time. This reaction occurs in Ar, Kr, and Xe matrices upon annealing above 25 K and may proceed over the barrier. The case of a Ne matrix is very special because the formation of trans-HOCO from the OHCO complex is observed even at the lowest experimental temperature (4.5 K), which is in sharp contrast to the other matrices. It follows that quantum tunneling is probably involved in this process in the Ne matrix at such a low temperature. Infrared light also promotes this reaction in the Ne matrix at 4.5 K, which is not the case in the other matrices. The last findings show the effect of the environment on the tunneling and infrared-induced rates of this fundamental chemical reaction.

Radiation-induced transformations of matrix-isolated formic acid: evidence for the HCOOH → HOCO + H channel.

The effect of X-ray irradiation on the isolated formic acid molecules (HCOOH) in solid noble gas matrices (Xe, Kr, Ar, and Ne) at very low temperatures (6 K) was first studied by FTIR spectroscopy. Carbon oxides (CO and CO2) and hydrocarboxyl radicals (HOCO) have been detected as the principal degradation products. The formation of HOCO radicals represents a primary dissociation channel for formic acid, which was not reported previously under UV photolysis in solids. This reaction can be explained by the involvement of the recombination-induced excited states, which are not populated in photolysis. The effects of the matrix and the absorbed dose on the product formation were studied in detail and possible mechanisms are discussed with particular attention to the difference between radiolysis and UV-photolysis of the matrix-isolated formic acid. The results obtained provide a new insight into the effects of high-energy impact on the simplest carboxylic acid with possible implications to the astrochemical problems, in particular, the prebiotic evolution in the interstellar medium.

Matrix-isolation studies on the radiation-induced chemistry in H2O/CO2 systems: reactions of oxygen atoms and formation of HOCO radical.

The radiation-induced transformations occurring upon X-ray irradiation of solid CO2/H2O/Ng systems (Ng = Ar, Kr, Xe) at 8-10 K and subsequent annealing up to 45 K were studied by Fourier transform infrared spectroscopy. The infrared (IR) spectra of deposited matrices revealed the presence of isolated monomers, dimers, and intermolecular H2O···CO2 complexes. Irradiation resulted in effective decomposition of matrix-isolated carbon dioxide and water yielding CO molecules and OH radicals, respectively. Annealing of the irradiated samples led to formation of O3, HO2, and a number of xenon hydrides of HXeY type (in the case of xenon matrices). The formation of these species was used for monitoring of the postirradiation thermally induced chemical reactions involving O and H atoms generated by radiolysis. It was shown that the radiolysis of CO2 in noble-gas matrices produced high yields of stabilized oxygen atoms. In all cases, the temperatures at which O atoms become mobile and react are lower than those of H atoms. Dynamics and reactivity of oxygen atoms was found to be independent of the precursor nature. In addition, the formation of HOCO radicals was observed in all the noble-gas matrices at remarkably low temperatures. The IR spectra of HOCO and DOCO were first characterized in krypton and xenon matrices. It was concluded that the formation of HOCO was mainly due to the radiation-induced evolution of the weakly bound H2O···CO2 complexes. This result indicates the significance of weak intermolecular interactions in the radiation-induced chemical processes in inert low-temperature media.

Photolabile xenon hydrides: a case study of HXeSH and HXeH.

The photo-induced transformations of HXeSH and HXeH under the action of IR and visible light have been studied using FTIR spectroscopy. The xenon hydrides were produced by the X-ray induced decomposition of H2S and its isotopomers in a solid xenon matrix at 7.5 K followed by thermal annealing at the temperatures up to 45 K. Selective IR-induced photodissociation of HXeSH at 3500-2500 cm(-1) was attributed to vibrational excitation of the 3ν(H-Xe) mode. The IR-photodecomposed HXeSH molecules can be almost quantitative recovered below 22 K with very small effective activation energy (~20 meV) indicating local character of this process. Analysis of the photoactivity of xenon hydrides in the visible region revealed previously unknown absorptions for HXeSH (in the region of 400-700 nm) and HXeH (above 700 nm). The decomposition of HXeH occurs due to both direct photolysis and reactions of "hot" H atoms produced from the photodissociation of HXeSH. The efficiency of thermal recovery for both xenon hydrides after photolysis with visible light was found to be dependent on the excitation wavelength, which was explained by the effect of photon energy on spatial distribution of the dissociation fragments.