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The total yield of emitted particles from solid CH4 and Ar matrices doped with CH4 was studied under irradiation with electrons. The explosive desorption was detected for these systems. Strong bursts of particles were delayed with respect to the start of irradiation indicating the need for accumulation of radiolysis products. The study was performed using optical and current spectroscopy – cathodoluminescence (CL) together with thermally stimulated exoelectron emission (TSEE) and thermally stimulated post-desorption (TSpD). In the CL spectra, the products of radiation-induced transformation of CH4 molecules were recorded: H, CH, C. Dose dependencies of the optical emissions were measured in a correlated manner with the total yield of particles. It was found that the particles burst correlates with an increase in the concentration of H atoms. Scenario suggested for the delayed particle emission incorporates the recombination of CH3 radicals appearing simultaneously with H atoms in the reaction CH4 → CH3 + H.

The radiation effects and relaxation processes in solid CH4 irradiated by an electron beam were studied with a focus on the beam-induced particle emission. The study was performed using cathodoluminescence (CL), monitoring of the total yield of particle emission and applying activation spectroscopy technique – thermally stimulated exoelectron emission (TSEE). Emissions of photons and particles under beam were monitored in a correlated style. Upon irradiation by 1 keV electron beam of 3 mA cm−2 current density we observed for the first time explosive particle emission which occurred with the delay of an hour with respect to the start of irradiation. Simultaneously with the particles outburst a CL flash was detected. Delay in the giant outburst of particles indicates the need for the accumulation of radiolysis products for this phenomenon. The critical dose for this effect is 100 eV per methane molecule. The outburst of particles is preceded by oscillations of particles emission with increasing amplitude. The period of these oscillations depends on the intensity of the irradiation, it decreases with an increase in the beam current density. Possible mechanisms of low-temperature explosive particle emission are discussed.

The total yield of particles desorption from solid Ar doped with CH4 under irradiation with an electron beam was studied at 5 K. The measurements were carried out at a CH4 concentration of 1 and 5%. The effect of explosive delayed desorption from the surface of argon matrix was discovered in both mixtures. With a higher concentration of CH4, it appeared at lower doses and was more pronounced. Two types of self-oscillations were observed: long-period bursts (on a time scale of about 25 min) and short-period oscillations (of about 10 s). In pure solid Ar delayed desorption was not observed despite the accumulation of a significant number of excess electrons, exceeding their number in mixtures of Ar and CH4 as it was found by measurements of thermally stimulated exoelectron emission. This finding discards the model of Coulomb explosion for the phenomenon detected. In this paper we focused on the role of hydrogen (one of the radiolysis products) in delayed desorption. The formation of atomic hydrogen in the matrix was traced via cathodoluminescence by the emission band of the excimer Ar2H* at 166 nm. Desorption of excited hydrogen atoms in the excited state was detected by the Ly-α emission line. A decrease of the Ar2H* band intensity at higher concentration of CH4 was found evidencing bleaching these centers likely due to recombination of H atoms with energy release and formation of molecular hydrogen. The data obtained give additional evidence in favor of the hypothesis that the exothermic reactions of radiolysis products serve as a stimulating factor for delayed desorption.

The radiation effects and relaxation processes in N2 and CH4 solids irradiated by an electron beam were studied with a focus on post-irradiation phenomena. The study was performed using optical and current spectroscopy methods: cathodoluminescence (CL) and developed by our group nonstationary luminescence (NSL) as well as nonstationary desorption (NSD) methods, together with activation spectroscopy techniques – spectrally resolved thermally stimulated luminescence (TSL), and thermally and photostimulated exoelectron emission (TSEE/PSEE). An afteremission of electrons was observed from N2 and CH4 solids pointing to an electrostatic charging of both films. The PSEE and TSEE from methane films were detected for the first time demonstrating important role of charge centers in radiation effects. Formation of negatively charged ions in methane by electron attachment was verified via PSEE followed by TSEE. Possible scenarios of N4+ and N3+ neutralization via dissociative recombination are discussed and data indicating space distribution of these centers are presented.

Recent findings on electronically induced processes in N 2 molecular solids monitored by luminescence methods are presented with a focus on the electronically induced desorption. Low-energy electron beam was used for excitation to avoid the knock-on defect formation and sputtering. The samples were probed with depth by varying electron energy. VUV photon emissions from desorbing N * atoms (the 4 P 1/2–5/2 → 4 S 3/2 transitions) under irradiation by electrons of subthreshold energy were observed for the first time. Their distinctive feature is a coincidence with the gas phase lines within the experimental error. New data on electronically stimulated desorption of N 2 * molecules in the electronic excited state C 3 Π u are reported. Monitoring of nonstationary desorption NsD in combination with the detection of thermally stimulated exoelectron emission TSEE and post-desorption reveal the contribution of charge recombination reactions in the electronically induced particles ejection. Fresh approach to study of electronically induced desorption opens new type of greatly delayed desorption associated with the entry of freeing electrons in recombination process.

Nonstationary processes in the Ar matrix doped with CH4 were studied with a focus on the behavior of radiolysis products – H atoms and CH radicals. Samples of 25 μm thickness were irradiated with 1.5 keV electron beam. It has been shown that because of the small penetration depth of electrons the bulk of the matrix is excited preferentially by photons with an energy of 9.8 eV, the most intense emission band of the matrix (excitons self-trapped into the configuration of Ar2∗), In other words “internal photolysis” occurs. The spectrally resolved emission of H atoms and CH radicals, along with the total yield of desorbing particles, were monitored in a correlated manner under the concurrent action of photons and external heating. These dependences, called nonstationary luminescence (NsL) and nonstationary desorption (NsD), were compared with the measured yield of thermally stimulated exoelectron emission (TSEE), that enabled us to reveal the appearance of the CH radical in the neutralization reaction CH3+ + e− → CH3∗ followed by dissociation of CH3∗. Thus, the CH radical was assumed to be a signature of the CH3∗ species. The antibate behavior of the CH NsL and the NsD in the temperature range 37–43 K, where diffusion in the Ar matrix occurs, was interpreted as a result of the recombination of CH3 radicals with the formation of C2H6 and the energy release spent for desorption. Self-oscillations (with τ of about 10 s) of increasing amplitude were detected, indicating self-oscillating processes in the bulk of the Ar matrix doped with 5% CH4.

The radiation effects and relaxation processes in pre-irradiated by an electron beam solid $$\hbox {N}_{2}$$ have been studied with a focus on the behavior of the so far unidentified emission band at 360 nm. The study was performed using optical and current spectroscopy methods: cathodoluminescence and developed by our group nonstationary luminescence, as well as spectrally resolved thermally stimulated luminescence, and thermally stimulated exoelectron emission. The measurements cover the temperature range of the $$\alpha $$ -phase existence. Activation spectroscopy evidenced connection of the 360 nm band with the neutralization reaction. Possible scenarios of $$\hbox {N}_{4}^{+}$$ neutralization via dissociative recombination are discussed, and interpretation of the 360 nm band is suggested.

Electrostatic charging of nanostructured N2 films was studied employing optical and a current set of emission spectroscopy methods: cathodoluminescence CL, thermally and photon-stimulated exoelectron emission TSEE, PSEE as well as thermally and photon-stimulated luminescence TSL, PSL. Concurrently with thermally stimulated yield of electrons the yield of nitrogen particles was detected, so-called “postdesorption.” An enhancement of the optical emission stemmed from the neutralization reaction N4+ + e → N2* + N2* → N2 + N2 + hν was observed with an exposure to an electron beam. The experiments performed with a variable voltage applied to an electrode for current detection demonstrated significant accumulation of negative charge. The TSEE current in the low-temperature range was detected at negative voltages up to −30 V. An accumulation of trapped electrons (up to 1016 cm−3) was detected. A possible contribution of N3− in electrostatic charging was assumed. Thermally stimulated yield of negatively charged particles from a N2 film subjected to an electron beam.

Monitoring of the cathodoluminescence spectra temporal evolution and concurrent measurements of optical and current relaxation emissions revealed stabilization and accumulation of the radiation-induced charged species. New results in favor of hole self-trapping with the tetranitrogen cation N 4 + formation are presented. “Fingerprints” of N 3 − species are detected by the photon-stimulated exoelectron emission.

Recombination of the intrinsic ionic centers Ne2+ (self-trapped holes) with the detrapped electrons in solid Ne matrices and relaxation channels have been studied. The experiments were performed employing combination of the cathodoluminescence (CL) with current and optical activation spectroscopy techniques. CL spectra were recorded simultaneously in the VUV and visible range. Yields of spectrally resolved thermally and photon-stimulated luminescence (TSL, PSL) and thermally and photon-stimulated exoelectron emission (TSEE, PSEE) were measured in the time-correlated manner. It was found that the recombination reaction proceeds with irreversible dissociation of the transient Ne2∗∗ centers and the dissociative recombination (DR) products exit the matrix cage. Products of the DR reaction are found to be in 3s and 3p states. The detection of “defect” components in the TSL and PSL points to the defect formation via DR in Ne matrices. The temperature range of the electron traps stability is elucidated. A long-lasting “afteremission” of electrons and afterglow of VUV photons observed on switching off the irradiation suggest the accumulation of the uncompensated negative charge.

Radiation effects in solid nitrogen irradiated with an electron beam were studied with emphasis on the role of charged centers in radiation-induced phenomena. The experiments were performed employing luminescence method and activation spectroscopy techniques – spectrally resolved thermally stimulated luminescence TSL and thermally stimulated exoelectron emission. Samples were probed in depth by varying electron energy, thus discriminating radiation-induced processes in the bulk and at the surface. Spectroscopic evidence of the excited N2* (C3Πu) molecule desorption was obtained for the first time and mechanism of the phenomenon based on recombination of electron with intrinsic charged center N4+ was proposed. The key role of N3+ center dissociative recombination in generation of N radicals is suggested. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The radiation effects and relaxation processes in solid N2 and N2-doped Ne matrices, preirradiated by an electron beam, have been studied in the temperature range of 5-40 and 5-15 K, respectively. The study was performed using luminescence methods: cathodoluminescence CL and developed by our group nonstationary luminescence NsL, as well as optical and current activation spectroscopy methods: spectrally resolved thermally stimulated luminescence TSL and exoelectron emission TSEE. An appreciable accumulation of N radicals, N(+), N2(+) ions, and trapped electrons is found in nitrogen-containing Ne matrices. Neutralization reactions were shown to dominate relaxation scenario in the low-temperature range, while at higher temperatures diffusion-controlled reactions of neutral species contribute. It was conceived that in α-phase of solid N2, the dimerization reaction (N2(+) + N2 → N4(+)) proceeds: "hole self-trapping". Tetranitrogen cation N4(+) manifests itself by the dissociative recombination reaction with electron: N4(+) + e(-) → N2*(a'(1)Σ(u)(-)) + N2 → N2 + N2 + hν. In line with this assumption, we observed a growth of the a'(1)Σ(u)(-) → X(1)Σ(g)(+) transition intensity with an exposure time in CL spectra and the emergence of this emission in the course of electron detrapping on sample heating in the TSL and NsL experiments.

Anomalous low-temperature post-desorption (ALTpD) from the surface of nominally pure solid nitrogen preliminary irradiated by an electron beam was detected for the first time. The study was performed using a combination of activation spectroscopy methods—thermally stimulated exoelectron emission (TSEE) and spectrally resolved thermally stimulated luminescence (TSL)—with detection of the ALTpD yield. Charge recombination reactions are considered to be the stimulating factor for the desorption from pre-irradiated α-phase solid nitrogen.

We have studied thermo-stimulated luminenscence and electron emission of nitrogen films and nanoclusters containing free radicals of atomic nitrogen. Thermo-stimulated electron emission from N2 nanoclusters was observed for the first time. Thermo-stimulated luminescence spectra obtained during the destruction of a N2–He sample are similar to those detected from N2 films pre-irradiated by an electron beam. This similarity reveals common mechanisms of energy transfer and relaxation. The correlation of luminescence intensity and electron current in both systems points to the important role of ionic species in relaxation cascades. Sublimation of solid helium shells isolating nitrogen nanoclusters is a trigger for the initiation of thermo-stimulated luminescence and electron emission in these nitrogen–helium condensates.

The chemistry of (H(2)O)(n)(•-), CO(2)(•-)(H(2)O)(n), and O(2)(•-)(H(2)O)(n) with small sulfur-containing molecules was studied in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry. With hydrated electrons and hydrated carbon dioxide radical anions, two reactions with relevance for biological radiation damage were observed, cleavage of the disulfide bond of CH(3)SSCH(3) and activation of the thiol group of CH(3)SH. No reactions were observed with CH(3)SCH(3). The hydrated superoxide radical anion, usually viewed as major source of oxidative stress, did not react with any of the compounds. Nanocalorimetry and quantum chemical calculations give a consistent picture of the reaction mechanism. The results indicate that the conversion of e(-) and CO(2)(•-) to O(2)(•-) deactivates highly reactive species and may actually reduce oxidative stress. For reactions of (H(2)O)(n)(•-) with CH(3)SH as well as CO(2)(•-)(H(2)O)(n) with CH(3)SSCH(3), the reaction products in the gas phase are different from those reported in the literature from pulse radiolysis studies. This observation is rationalized with the reduced cage effect in reactions of gas-phase clusters.

Charging effect and relaxation processes in cryogenic solids pre-irradiated by an electron beam are discussed with the example of solid Xe. The experiments were performed employing combination of the cathodoluminescence method with activation spectroscopy techniques: thermally stimulated luminescence (TSL) and thermally stimulated exoelectron emission (TSEE). Relaxation emissions of photons and electrons were detected in the time correlated manner. A long-lasting “afteremission” of electrons and afterglow of VUV photons were observed on completing irradiation. The experiments performed with a variable voltage applied to the Faraday plate enabled us to demonstrate appreciable accumulation of electrons and ascertain the spatial distribution of the charge centers. The uncompensated negative charge is found to be localized preferentially near the surface. Xe layers close to the sample-substrate interface are shown to be positively charged. The part played by pre-existing and radiation-induced defects as well as dopants is considered and the temperature range of the electron traps’ stability is elucidated.

Having closed valence sub-shells, the alkaline earth atoms participate in covalent bonding via orbital hybridization and exchange interactions, with additional contributions from dispersion interactions. Starting from a closed ns2 configuration imparts different characteristics to the chemistry of this group, as compared to metals that have open-shell atomic ground states. Theoretical studies of the bonding of the Group IIA metals have been pursued for many years, and they are known to be challenging for ab initio electronic structure methods. The bonding motifs have been examined, and the differences between beryllium and the remainder of the group explored. Experimental studies that probe the bonding, particularly for beryllium, have lagged behind the theoretical work. In the present Letter we describe our recent spectroscopic and theoretical investigations of simple beryllium compounds, and discuss these results in terms of their relationship to the properties of the heavier Group IIA elements.

Radiation effects and relaxation processes in atomic solids are discussed with the example of solid Xe preliminarily irradiated by an electron beam. The study was performed employing concurrently the combination of current and optical “activation spectroscopy” methods. Three relaxation processes were monitored simultaneously upon controlled warming-up of pre-irradiated solids: thermally stimulated exoelectron emission (TSEE), thermally stimulated luminescence (TSL) in the VUV range and the total desorption yield by pressure measuring above the sample. Anomalous strong low-temperature “post-desorption” (ALTpD) of own atoms from pre-irradiated Xe solids was observed for the first time. The data obtained demonstrated a clear correlation between the yields of exoelectrons, photons of recombination luminescence and neutral particles pointing to the common origin of the phenomena. It was shown that the key primary process of the relaxation cascade including the ALTpD is a thermally stimulated electron detrapping, promoting electrons into the conduction band. Subsequent branching of the relaxation paths results in the relaxation emissions observed. An accumulation of charges of both signs as well as excess electrons under exposure to an electron beam was found.

The formation of excimers (Xe2H)* in solid Xe doped with molecular hydrogen under irradiation by an electron beam is studied using the original two-stage technique of nonstationary (NS) cathodoluminescence (CL) in combination with current activation spectroscopy—thermally stimulated exoelectron emission (TSEE). Charged species are generated using a high-density electron beam. The species produced are probed with a low-density beam with sample gradually heated. The near-UV emission of the (Xe2H)* is used to monitor the neutralization process. It is found that the temperature behavior of the NS CL band of (Xe2H)* clearly correlates with the yield of TSEE measured after identical pre-irradiation of the sample. The fingerprints of the thermally stimulated detrapping of electrons—«internal electron emission»—-in the spectrum of NS CL point to the essential role of the neutralization reaction in the stability of protons solvated by rare-gas atoms.

The relaxation processes in oxygen-containing Rare Gas Solids (RGS) pre-irradiated by a low energy electron beam are studied with the focus on the role of diffusion-controlled atom-atom recombination reaction in the relaxation cascades. The results of correlated in real time measurements of thermally stimulated phenomena are presented. The experiments were performed using activation spectroscopy methods–spectrally resolved thermally stimulated luminescence (TSL) and exoelectron emission (TSEE). The suggested mechanism provides a long-range energy transfer and demonstrates the existence of a new relaxation channel–triggering of electronic relaxation processes by diffusion-controlled atom-atom recombination reaction followed by the emission of photons in the visible range which is converted due to the relaxation process into a vacuum ultraviolet (VUV) emission.

2 Be or Not 2 Be? The beryllium dimer is a rather simple-looking compound, bridging two atoms of the fourth-lightest element. Yet it has long posed a frustrating challenge to theorists, because, to a first approximation, chemical bonding models suggest that it should not exist. In recent decades, calculations of ever-increasing sophistication have offered rationales for the two atoms' puzzling mutual attraction. Now Merritt et al. (p. 1548 , published online 21 May; see the Perspective by Bernath ) have used high-resolution spectroscopy to assemble, at last, a full experimental potential energy function describing the ground electronic state of Be 2 . The curve is unusually shallow at long bond lengths, deviating from the contour of more traditional molecular Morse potentials, and provides a detailed basis of comparison for future theoretical bonding frameworks.

The processes of energy relaxation in rare gas solids pre-irradiated with an electron beam are discussed. The emission of exoelectrons and photons from rare gas solids is studied. Investigations are performed by a set of activation spectroscopy methods applied simultaneously to each sample. Photon-stimulated exoelectron emission from solid Ne is observed for the first time.

Correlated real-time measurements of thermally stimulated luminescence and exoelectron emission from solid Xe pre-irradiated with an electron beam are performed. The study enables us to distinguish between surface and bulk traps in solid Xe and to identify a peak related to electronically induced defects. The activation energy corresponding to annihilation of these defects is estimated by the following methods: the method of different heating rates, the initial-rise method, and the curve cleaning technique with fitting of the thermally stimulated luminescence glow curve.

A novel design for a temperature-controlled ICR cell is described for use in black-body infrared radiative dissociation (BIRD) studies of weakly bound systems like water clusters. Due to several improved design features, it provides a very uniform black-body radiation environment, and at the same time maintains efficient pumping for a low collision rate on the order of 10 −2 s −1 . At the lowest temperatures reached, nominally 89 K cell plate temperature, water evaporation effectively ceases, while intracluster reactions in V + (H 2 O) n with a small activation energy are still observed. BIRD rate constants for Ag + (H 2 O) n , n = 4–6, are shown in the temperature range T = 160–320 K. For n = 6, a linear Arrhenius plot with R 2 = 0.9943 is obtained without any calibration, confirming the suitability of the cell for quantitative BIRD studies.

Relaxation processes in films of solid Ar irradiated with low-energy electrons were studied with emphasis on the recently found phenomenon – anomalous low temperature desorption (ALTD) of rare gas atoms from pre-irradiated rare gas solids. A combination of optical and current activation spectroscopy methods were used; thermally stimulated luminescence, thermally stimulated exoelectron emission as well as measurement of the total desorption yield. The measurements were performed simultaneously in real time. Analysis of the data provides solid evidence of a two-stage mechanism for ALTD: (i) thermally assisted release of electrons from their traps followed by (ii) intrinsic charge recombination. The dose behavior and efficiency of the ALTD in comparison with desorption induced by electronic transition under an electron beam is discussed.

Spatially separated stable charge centers, self-trapped holes and trapped electrons, were generated in Ar cryocrystals by a low-energy electron beam. A combination of the cathodoluminescence (CL) and photon-stimulated exoelectron emission (PSEE) methods was used to monitor center formation and a selected relaxation channel—exoelectron emission. It was found that photon-promoted electron current decreased exponentially under irradiation with the laser operating in the visible range. The influence of the laser parameters (power and wavelength) on the characteristic lifetime of exoelectron emission is discussed. Effective bleaching of the low-temperature peaks of thermally stimulated exoelectron emission by the laser light in a visible range is observed.

A new modification of low-temperature activation spectroscopy technique for real-time correlated study of relaxation processes in cryogenic solids is developed. This enables us to measure simultaneously the thermally stimulated exoelectron emission (TSEE) and spectrally resolved thermally stimulated luminescence (TSL) in the range from 200 to 1100nm. This paper presents the results on TSL and TSEE from solid Ar doped with N2 exposed to irradiation by a low-energy electron beam (500eV) during deposition. The TSEE and TSL yields were measured at a heating rate of 3.2K∕min. The emissions of molecular (A3Σu+→X1Σg+ transition) and atomic (D2→S4 transition) nitrogen in the TSL spectra and their temperature behavior were studied. Drastic changes in the intensity distribution of the molecular progression are observed with temperature rise. In the low-temperature range, “hot” vibrationally unrelaxed transitions are detected, in contrast to “cold” vibrationally relaxed transitions observed in “high”-temperature TSL...

Spatially separated stable charge centers – self-trapped holes, trapped electrons, dopant ionic centers and radicals were generated in an Ar matrix doped with Xe and N2 by a low energy electron beam. A combination of the cathodoluminescence (CL) with the photon-stimulated luminescence (PSL) and photon-stimulated exoelectron emission (PSEE) methods was used to monitor center formation and selected relaxation channels – charge recombination reactions and exoelectron emission. PSEE from pre-irradiated Ar samples was registered simultaneously with N line emission. Vacuum ultraviolet (VUV) intrinsic and extrinsic recombination luminescence from pre-irradiated samples has been detected to confirm the suggested relaxation path of the stored energy. An afterglow of the N line can be considered as an internal source of photons which releases electrons from the traps and being a triggering mechanism of relaxation processes: (i) – exoelectron emission, (ii) – radiative recombination of charge species. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Correlation studies of thermally stimulated luminescence (TSL) and thermally stimulated exoelectron emission (TSEE) from solid Ar pre-irradiated with an electron beam are presented. Measurements were performed using different heating modes – step-wise heating and heating with a constant rate. Influence of pre-existing defects and dose effect on TSL and TSEE are considered. TSEE active layer is estimated. Correlation between TSL and TSEE phenomena pointing to the common primary process – release of electrons from the same kind of traps, is clearly demonstrated. Competition between TSL and TSEE is discussed. It was found that TSEE predominates at low temperatures and in the range of sublimation. Long time irradiation suppressed the total yield of exoelectrons. The part of chemiluminescent reactions in relaxation cascades is elucidated. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; The reactions of water cluster anions (H2O)n-, n = 30-70, with hydrogen chloride have been studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The first HCl taken up by the clusters is presumably ionically dissolved. The solvated electron recombines with the proton, which is thereby reduced to atomic hydrogen and evaporates from the cluster. This process is accompanied by blackbody radiation and collision induced loss of water molecules. Subsequent collisions lead to uptake of HCl and loss of H2O, yielding mixed clusters Cl-(HCl)m(H2O)n until they are saturated with HCl. Those saturated clusters lose H2O and HCl in a characteristic sequence. The final stage of the reaction, involving clusters with m = 0-4 and n = 0-6, is studied in detail with density functional theory calculations. The Cl-(HCl)4(H2O)6 cluster represents an example for supramolecular self-organization in the gas phase: it consists of a tetrahedral Cl-(HCl)4, connected on one side of the tetrahedron to a compact water hexamer. © 2007 American Chemical Society.

Relaxation processes in oxygen-containing Ar cryocrystals pre-irradiated by low-energy electrons are studied with the focus on the role of the diffusion-controlled atom-atom recombination reaction of oxygen in the relaxation cascades. The results of real-time-correlated measurements of thermally stimulated phenomena are presented. The experiments have been performed using activation spectroscopy methods—thermally stimulated exoelectron emission and spectrally resolved thermally stimulated luminescence. Solid evidence for the radiative mechanism of electron detrapping triggering the relaxation cascades is obtained.

The reactivity of cationic rhodium clusters, Rhn+, n = 1–23, with ethane is studied by Fourier transform ion cyclotron resonance mass spectrometry. Single and double dehydrogenation with elimination of molecular hydrogen are the reactions observed. The reaction efficiency and branching ratio are strongly dependent on cluster size. The behavior is attributed to geometric effects, suggesting that dehydrogenation of ethane on cationic rhodium clusters has strong steric requirements.

Bimolecular reactions of cationic platinum clusters Ptn+, n = 1–24, and anionic platinum clusters Ptn−, n = 3–22, with CH4 and CD4 are studied under low pressure conditions in an FT-ICR mass spectrometer, using an isotopically enriched 195Pt sample. Strongly size-dependent dehydrogenation and formation of PtnCH2+/− is observed for both charge states. Starting with n = 12, cationic clusters also afford stabilization of a [Ptn, CH4]+ adduct, presumably the HPtnCH3+ insertion compound. Deuteration shifts the lower limit for adduct formation to n = 8. It is suggested that the strong reactivity fluctuations over a wide size range are the gas phase fingerprint of a good heterogeneous catalyst material.

Sputtering of Ar atoms from the surface of nominally pure and O2 doped solid Ar, preliminary irradiated by an electron beam, is studied using a combination of activation spectroscopy methods — thermally stimulated luminescence (TSL) and thermally stimulated exoelectron emission (TSEE) — with measurements of the sputtering yields. Anomalous yield of Ar atoms was detected at temperatures much lower than the characteristic sublimation temperature of solid Ar. A charge recombination reaction is considered to be the stimulating factor for the low temperature desorption from preirradiated solid Ar. Possible models of the anomalous sputtering are discussed and the crowdion mechanism of the atom ejection from the surface is proposed. The influence of oxygen on the sputtering yield is considered.

The role for the exciton-induced defects in the stimulation of anomalous low-temperature desorption of the own lattice atoms from solid Ar and Ne preirradiated by an electron beam is studied. The free electrons from shallow traps—structural defects—was monitored by the measurements of a yield of the thermally induced exoelectron emission (TSEE). The reaction of recombination of self-trapped holes with electrons is considered as a source of energy needed for the desorption of atoms from the surface of preirradiated solids. A key part of the exciton-induced defects in the phenomenon observed is demonstrated.

The recent observation of organic Xe compounds, in particular XeC2 and HXeCCH, in rare gas matrices have stimulated us to search for the BN isoelectronic analogues of these compounds. Here we present quantum chemical calculations using density functional theory on XeBN (XeNB), as well as Xe insertion into iminoborane to form HXeBNH and into borazine forming HXeB3N3H5. In both cases, insertion into NH and BH bonds were considered and their relative stability compared. For iminoborane, doubly-inserted Xe was also treated and for borazine, both doubly and triply inserted.

Relaxation processes and stability of charge centers in preirradiated cryocrystals doped with atomic and molecular species are discussed. The study was performed combining techniques of spectrally resolved thermally stimulated luminescence (TSL), thermally stimulated exoelectron emission (TSEE) and photon-stimulated exoelectron emission (PSEE). Comparison of the yields of electrons and photons in VUV and visible ranges made it possible to discriminate between reactions of charge carriers and neutral reactive species and find interconnection between atomic and electronic processes of relaxation. The radiative mechanism of electronic relaxation stimulation via an atomic subsystem is verified.

In the present manuscript we review the chemistry of aqueous electrons, as studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. FT-ICR studies of the (H 2 O) n − reactions have the advantage that compared with bulk solutions the electrons exhibit long lifetimes, and impurity effects can be completely eliminated. The review demonstrates that aqueous electrons, the simplest chemical reagents, exhibit a multifaceted chemistry, and may provide new insights into the aqueous chemistry of neutral and anionic radicals. We show that the cluster reactions can be loosely classified into several categories, and give representative examples for each of them.

An H/D-exchange reaction involving the methyl group of acetonitrile is observed in the small anionic water cluster OH-(CD3CN)(H2O)2. In this cluster, a randomization of H and D atoms takes place, and in subsequent collisions with CD3CN, the potentially partially deuterated acetonitrile is replaced by the fully deuterated species. In sequential collisions, fully deuterated clusters OD-(CD3CN)(D2O)2 are obtained as final products. The H/D-exchange does not occur in OH-(CD3CN)(H2O)3 or larger clusters. Density functional calculations show that in these larger species, the OH- no longer directly attacks the methyl group, and the barriers for H/D-exchange become higher than those for ligand loss reaction channels. This is a very subtle influence of solvation on an H/D-exchange reaction in the gas phase, where a relatively acidic methyl group encounters a strongly basic reaction partner.

A self-igniting DC-electric discharge of C2H2 in Xe (matrix gas) or C2H2 and Xe in Ar or Kr (matrix gas) is used to produce and study the XeC2 molecule in these various rare gases at 12 K. Unlike in Ar and Kr, the well-known electronic spectra of C2 is completely absent in a Xe matrix. This together with annealing experiments in Ar matrices indicate that ground state Xe and C2 react uniquely and without a barrier to form the XeC2 molecule. The IR-active C-C stretch of this compound is found to be close to the C-C stretching frequency of the C2 anion, in excellent agreement with our density functional theoretical (DFT) calculations, which yield a XeCC singlet species bent by 148.6° and with substantial charge separation approaching Xe+C2– and a notably short (2.107 Å) Xe—C bond. The spectra of the Xe–13C–12C, Xe–12C–13C, and Xe–13C–13C species are also obtained and the isotopic shifts are in excellent agreement with the DFT predictions, although not sufficient to distinguish a bent from a linear structure. Numerous broad absorptions centered near 423 nm (in Xe) are observed, which are clearly due to the XeC2 molecule. Laser-induced fluorescence studies reveal a near-IR emission likely due to XeC2 but not yet understood. Infrared spectra in the Xe matrix reveal also formation of the HXeCCH molecule.Key words: matrix-isolation spectroscopy, rare gas compounds, charge transfer compounds, xenon–carbon bonds.

Gas-phase reactions of anionic and cationic rhodium clusters with azidoacetonitrile are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry under near-thermal conditions...

Cationic and anionic clusters 195Ptn±, 1 ≤ n ≤ 24, were generated by laser vaporization using an isotopically enriched platinum sample. The oxidation of the clusters by nitrous oxide under binary collision conditions was investigated as a function of charge and size in a Fourier transform ion cyclotron resonance mass spectrometer. The only reaction observed is sequential addition of an oxygen atom, with the loss of molecular N2. The reaction rates as well as the number of reaction steps exhibit a strong and irregular dependence upon the number of atoms in the cluster and its charge. These results show that isotopically enriched samples allow for the investigation of large cluster sizes together with an unambiguous assignment of reaction products and quantitative determination of rate constants.

Cold M n ± group 5 (V, Nb, Ta) and group 9 (Co, Rh, Ir) cationic as well as anionic clusters with up to about 30 atoms were produced by laser vaporization in supersonic expansion, and their reactivity with carbon monoxide was investigated in an FT-ICR mass spectrometer under conditions of bimolecular collisions. Anionic and cationic clusters of the later, group 9 transition metal elements, as well as cations of group 5 exhibit very similar behavior and trends. While the smallest species, n ≤4 are almost unreactive under the conditions of our experiment, for larger clusters above n =5 the rate of CO attachment increases abruptly by at least three orders of magnitude. On the other hand, a strikingly different behavior is found for the group 5 anion clusters, V n − , Nb n − , and Ta n − . For these elements, the threshold for anion cluster reactivity is significantly shifted from n =5 to much larger sizes, with the abrupt rise in reactivity occurring only above n =14–15. Possible reasons for the drastic difference in reactivity between the earlier and later transition metal anion clusters are discussed.

Energy relaxation processes in films grown from pure Ar gas and O2–Ar mixtures preliminary irradiated by an electron beam were studied with a focus on the role of radiative electronic transitions in the relaxation cascades. A combination of luminescent spectroscopy methods (thermally stimulated luminescence (TSL) including spectrally resolved TSL and cathodoluminescence) with thermally stimulated exoelectron emission technique was used. New additional data were obtained in a favor of the radiative mechanism of electronic relaxation processes––electron detrapping and transport followed by exoelectron emission and charge recombination. Correlation in the electron and in the low temperature desorption yields is clearly demonstrated. Suppression of the desorption from oxygen-containing films was found in contrast to the effect observed under excitation.

Absolute bimolecular rate constants for radiative stabilization of CO on gold cluster anions are measured by Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry, employing a sequence of reaction gas pulses to acquire sufficient product intensities of these exceedingly inefficient reactions. While some of the observed reactivity patterns seem to be in agreement with the jellium model if CO is viewed as a two electron donor, it cannot provide an explanation for some other observations, for instance for the secondary reactions of Au10− and Au11−. Interesting cooperative effects are observed in conjunction with O2, which is present as a trace component of the reaction gas. No evidence is found for catalytic CO2 formation on the clusters.

“Nanodroplets” consisting of a central ion surrounded by a solvation shell of water molecules provide an interesting medium for studies of aqueous transition-metal chemistry in the unusual oxidation state (I). While VI undergoes efficient, solvent shell dependent redox reactions to VII and VIII, the absence of any similar reactivity in aqueous CrI, MnI, FeI, CoI, NiI, and CuI clusters is explained by a rapid precipitation of the corresponding single monochloride molecules from the nanosolutions.

The reactions of hydrated aluminum ions Al(H2O)(n)(+), 20

The lifetimes of high Rydberg states of the methyl halides CH3I, CH3Br and CH3Cl have been studied. A pulsed dye laser tuned near half the ionization energy was used, with preprogrammed field pulses, and the high Rydberg states of the compounds in selected ranges of n values were ionized after a variable delay. Plots of the electron signal versus delay yielded information about the Rydberg state lifetime. The clearest trend was found for around n = 120–160: the lifetimes of the states decreased by more than an order of magnitude from CH3I (τ ≈12.3 μs) through CH3Br to CH3C1. Within the range studied, the theoretically predicted increase in lifetimes (n 5 or n 3) was not found, and in fact the highest group of states studied (with n > 215) exhibited for all three compounds relatively short lifetimes (≈2-3 μs), possibly due to collisional processes.

Branching of energy relaxation paths in metastable preirradiated solid Ar doped with O2 was studied using a combination of activation spectroscopy methods––thermally stimulated luminescence, thermally and photon-stimulated exoelectron emission. Analysis of the data obtained made it possible to discriminate between surface and bulk electron traps, to elucidate elementary processes involved in the relaxation cascade and to verify the radiation mechanism of energy conversion and transfer from atomic subsystem to electronic one. It was found that recombination of neutral O atoms results in promotion of electrons into the conduction band. A new effect was observed––low temperature desorption from preirradiated solid Ar. It was suggested the effect is due to thermally assisted charge recombination. 2002 Elsevier Science B.V. All rights reserved.