Float-zone and Czochralski-grown silicon crystals have been implanted with protons or deuterons. Electron-paramagnetic-resonance measurements performed during illumination with light at 1064 nm reveal a signal, labeled DK5, in addition to the well-known signal from VO*-the excited spin-triplet state of the oxygen-vacancy defect. The DK5 signal originates from a spin-triplet state of a vacancy-type defect with monoclinic-I (near-orthorhombic-I) symmetry. In contrast to the VO* signal, DK5 has about the same intensity in the spectra recorded on oxygen-lean and oxygen-rich samples, which indicates that the DK5 defect is not oxygen related. However, the close resemblance between the D tensors of DK5 and VO* strongly suggests that the electron-spin distributions are similar in the two defects. Moreover, anisotropic hyperfine splittings from two proton spins are partially resolved in the DK5 signal. The signal is assigned to VH2*, the excited spin-triplet state of the silicon vacancy containing two hydrogen atoms, which is the simplest defect consistent with the observed properties. The isochronal annealing behavior of DK5 coincides with that of two infrared-absorption lines at 2063 and 2077 cm-1, which, like DK5, are observable only during illumination. These lines are assigned to Si-H stretch modes of VH2*.

An EPR signal observed in carbon-doped float-zone silicon after irradiation with 2-MeV electrons at room temperature has been investigated. It represents a defect with S = 1/2, an apparently isotropic g factor (=2.0030), and a complicated hyperfine structure from Si-29 nuclei in five shells that are consistent with an overall trigonal symmetry. Subtle asymmetries of the hyperfine pattern indicate the presence of a small trigonal component of the g tensor as well. An additional pair of satellite lines is identified by the relative intensity (1%) as arising from C-13 in natural abundance, occupying two equivalent sites on the trigonal axis. Several defect structures that contain two equivalent carbon atoms on a trigonal axis were investigated by ab initio Hartree-Fock calculations. Only the negative charge state of a dicarbon center C-s-C-s, in which the carbon atoms occupy adjacent substitutional sites, was found to be consistent with the EPR data.

Infrared absorption measurements on n-type silicon doped with carbon and irradiated with electrons at room temperature have revealed new absorption lines at 527.4 and 748.7 cm(-1), which originate from the same defect. The 748.7-cm(-1) line is observed only when the sample is cooled in the dark and the spectrum is measured through a low-pass filter with cutoff frequency below 6000 cm(-1). Light with frequency above 6000 cm(-1) removes this line and generates the 527.4-cm(-1) line. Comparison with spectra recorded on irradiated cm silicon doped with C-13 shows that the two lines represent local vibrational modes of carbon. The annealing behavior of the 748.7-cm(-1) line is identical to that of the EPR signal originating from the negative charge state of two adjacent substitutional carbon atoms (C-s-C-s)(-). The 527.4- and 748.7-cm(-1) lines are ascribed to the E modes of C-s-C-s in the neutral and negative charge states, respectively. The structure and local vibrational modes of (C-s-C-s)(0) and (C-s-C-s)(-) have been calculated by ab initio local density functional theory. The calculated structures agree qualitatively with those obtained previously by Hartree-Fock methods, but the calculated Si-C and C-C bond lengths differ somewhat. The calculated local mode frequencies are in good agreement with those observed. The formation of C-s-C-s has also been investigated. It is suggested that the center is formed when a vacancy is trapped by the metastable substitutional carbon-interstitial carbon center, C-s-C-i.

n- and p-type float-zone silicon containing 10(18)-cm(-3) tin were irradiated with 2 MeV electrons to a dose of 10(18) cm(-2) and subsequently examined by electron paramagnetic resonance (EPR). The p-type material yields only the well-known Si-G29 signal due to the tin-vacancy complex SnV0, whereas the as-irradiated n-type material in addition displays the Si-G7 signal (V-2(-)), DK4, recently assigned to SnV- in a set of slightly inequivalent configurations, and a new signal DK1, from a defects with S = 1/2 containing one tin nucleus. DK1, which we assign to (SnV-V)(-), undergoes a reversible triclinic-monoclinic transformation at approximate to 15 K. Annealing at 428 K removes Si-G29 and DK4 and produces a six-fold increase of Si-G7 and DK1, the kinetics indicating that about 50% of SnV is transformed into V-2 and (SnV-V). Annealing at 503 K destroys Si-G7 and DK1, the decay of DK1 being linked to the emergence of two new signals DK2 and DK3 from defects with S = 1/2, monoclinic-l symmetry, and two equivalent tin nuclei each, which we identify as (SnV-VSn)(-) and (Sn2V-V)(-). The structures of the tin-divacancy complexes are discussed in terms of modifications imposed on the basic divacancy structure by the larger size and lower ionization potential of the tin atom as compared to silicon. A model is proposed for the migration of (SnV-V) in the lattice at 500 K, indicated by the process (SnV-V)+Sn-->(SnV-VSn).

Float-zone and Czochralski-grown silicon crystals have been implanted with protons or deuterons at similar to 50 K. Electron paramagnetic resonance measurements reveal a new signal in the spectrum of the Czochralski-grown (oxygen-rich) material. This signal is strongly temperature dependent, displaying a transition from monoclinic-I to orthorhombic-I symmetry in the temperature ranges 180-240 K and 230-290 K in the proton-and deuteron-implanted samples, respectively. The g tensor observed at low temperature as well as a large Si-29 hyperfine splitting associated with a unique silicon site are typical of a vacancy-type defect with the unpaired electron confined to a dangling-bond orbital. Proton hyperfine splittings show that a single hydrogen atom is incorporated in the defect and strongly suggest that the defect contains only one vacancy. The observations allow an unequivocal assignment of the signal to VOH0, the neutral charge state of the monovacancy-oxygen defect (the A center) containing a single hydrogen atom. It is found that the hydrogen atom may jump rather easily between the two equivalent sites lying in the (110) mirror plane of the defect.

Electron paramagnetic resonance measurements on proton- and deuteron-implanted silicon crystals reveal a new signal from a vacancy-type defect with spin S = 1/2, which is observable only in oxygen-rich material. The signal is strongly temperature-dependent, displaying monoclinic-l symmetry below 180 K and orthorhombic-l symmetry above 240 K in the proton-implanted samples. Resolved proton-hyperfine splittings show that a single hydrogen atom is located similar to 2.5 Angstrom from the silicon atom carrying the dangling bond. The observed properties, including the change of symmetry, allow an unambiguous identification of the signal with VOH0, the neutral charge state of the monovacancy-oxygen complex (known as the A center) binding one hydrogen atom. The hydrogen atom is observed to jump readily between two equivalent sites in the (1 1 0) mirror plane of the defect. (C) 1999 Elsevier Science B.V. All rights reserved.

The photolysis of aqueous CS2 has been studied using subpicosecond transient absorption spectroscopy. CS2 was photolyzed at 6.2 eV and the fast formation and decay of the photoproducts were monitored from 6.2 to 3.96 eV. Upon excitation, aqueous CS2 dissociates into CS+S. However, 93%±2% of the fragments geminately recombine on the electronic ground state potential of CS2 within a few picosecond leaving only 7%±2% of the CS+S fragments separated 100 ps after the excitation. In the gas phase, most of the dissociation occurs on a triplet-state potential surface, and the high recombination yield observed in aqueous solution therefore indicates a strong, solvent-assisted coupling between this state and the singlet ground state of CS2. The vibrationally excited CS2 molecule formed by the recombination transfers its high excess energy to the surrounding water molecules in two processes with time constants 8.4±1 and 33±7 ps. The rotational reorientation time of ground state CS2 is 6±1 ps, suggesting a surprisingly strong interaction between the neutral, nonpolar CS2 and the surrounding water molecules.

A model is proposed for the mechanism of reaction of the hydrated electron with strongly oxidizing inorganic oxocompounds, according to which such reactions comprise three steps: (1) a primary split-off of O- occurring immediately upon the transfer of the electron to the oxocompound, (2) after which O- becomes fully solvated, acquiring properties as in the bulk phase, and (3) finally, the solvated O- either escapes from the cage or forms an electron adduct by reacting back within the cage with its partner. The model is based on studies of the photochemistry of aqueous solution of the oxoanions O-3(-) and ClO3- (Walhaut, P. K.; Silva, C.; Barbara, P. F. J. Phys. Chem. 1996, 100, 5188. Klaning, U. K.; Sehested, K. J. Phys. Chem. 1991, 95, 740.), which suggest that solvation of the photoproduct O- precedes cage-back reactions. Measurements of the reactions of the hydrated electron with the perbromate ion and the periodate ion and of the reactions of O- with the bromate and iodate ion support the model by verifying that no electron adduct is formed unless O- and its partner react in the bulk phase at a diffusion-controlled rate.

Electron paramagnetic resonance measurements on float-zone silicon implanted with protons at similar to 50 K followed by heating to room temperature have revealed two signals S1(a) and S1(b), belonging to the S1 group of signals. S1(a) and S1(b) both originate from defects with spin S = 1/2 and monoclinic-I symmetry. The near-trigonal g tensors and several sets of Si-29 hyperfine splittings all closely resemble those observed previously for VH0, the neutral charge state of the monovacancy binding a single hydrogen atom. Analysis of a tiny proton hyperfine splitting of S1(a) provides strong evidence that this signal originates from V2H0, the neutral charge state of the divacancy binding one hydrogen atom. Parallel studies of the thermal decays of the VH0, S1(a), and S1(b) signals and of infrared-absorption lines associated with Si-H stretch modes indicate that VH0 possesses a stretch mode at 2038.5 cm(-1), whereas modes at 2068.1 and 2073.2 cm(-1) originate from the S1(a) and S1(b) defects. On the basis of theoretical results, we argue that the 2068.1-cm(-1) mode arises from V2H0 (the S1(a) defect) whereas the 2073.2-cm(-1) mode probably belongs to VnH0, n = 3 and 4 (the S1(b) defect).

The photolysis of aqueous C1O2 has been studied with a new femtosecond transient absorption spectrometer, allowing absorbance changes as small as ΔA 1 × 10-4 to be recorded with a time resolution of 150 fs. ClO2 was photolyzed at 390 nm and the ultrafast formation and decay of photoproducts were monitored from 230 nm to 78 nm, using either harmonics of the 780 nm pulses or a white light continuum. The main photolytic product, ClO + O, is formed with a quantum yield of 0.9, but disappears through a fast geminate recombination, producing vibrational excited C1O2 in the electronic ground state. The hot ClO, subsequently cools down in 10 ps. In addition to ClO + O, Cl + O2 is formed, with a quantum yield of 0.1 within the first 10 ps of the photolysis pulse, thus indicating the absence of the expected long-lived ClOO species. Using a simple model including the vibrational cooling of C1O2 and the absorbance of aqueous Cl we are able to account for the experimental observations.

The electron paramagnetic resonance spectrum of float-zone silicon recorded after implantation with protons contains a strongly temperature dependent signal from a vacancy-type defect. The signal displays monoclinic-I symmetry below 65 K and trigonal symmetry above 100 K. This symmetry change, together with a hyperfine splitting from a single proton, allows an unequivocal identification with VH0, the neutral charge state of a vacancy containing a single hydrogen atom. The striking similarity between the properties of VH0 and VP0 (the E center) corroborate our identification.

Floatzone grown silicon crystals have been implanted with protons or deuterons. Electron Paramagnetic Resonance (EPR) spectra show the presence of a strongly temperature dependent signal in addition to the well-known S1 signal. The temperature dependent signal displays monoclinic-I symmetry below 65 K and trigonal symmetry above 110 K. The g- and Si-29 hyperfine tensors are characteristic of defects with the unpaired electron confined mostly to a dangling bond orbital in a vacancy-type defect. The signal shows splittings arising from the hyperfine interaction with a single proton. On this basis, and from the close similarity with the familiar VPO signal (the E-center), we conclude that the signal originates from VHO, the neutral charge state of the silicon monovacancy containing a single hydrogen atom.

Photolysis at 6 K of OClO trapped in a single crystal of KClO4 produces the isomer ClOO in three inequivalent configurations A, B, and C. A and B are metastable, the conversions A --> B and B --> C occurring at similar to 35 and similar to 60 K, respectively. Comparison of observed values of the O-O stretching frequency nu(1) with those reported for ClOO matrix-isolated in argon and the geometry deduced from the spin Hamiltonians both suggest that ClOO in the stable configuration C is only slightly perturbed by the KClO4 lattice while stronger perturbations occur in configurations A and B. Hence, the spin Hamiltonian obtained for C should represent the properties of the free ClOO molecule to a good approximation. The matrix effects observed for A and B are attributed to polarization of ClOO, transferring electronic charge from Cl to O-2.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotoinduced addition of oxygen ion (O-) to perbromate in a crystalline matrix: a pentacoordinated bromine(VIII) species studied by ESRJ. R. BybergCite this: Inorg. Chem. 1993, 32, 24, 5513–5516Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://doi.org/10.1021/ic00076a017RIGHTS & PERMISSIONSArticle Views30Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (412 KB) Get e-Alerts Get e-Alerts

Photolysis at 633 nm below 45 K of the radiation-produced species BrO42- in solid KBrO4 generates a paramagnetic species with a spin Hamiltonian very similar to that of the pentacoordinated species IO52-. This strongly indicates a photoinduced transfer of O- from BrO42- to an adjacent BrO4-, where O- becomes attached to the bromine atom to form BrO52-, a trigonal, pentacoordinated bromine(VIII) analog of IO52-. The formation of BrO52- shows that the 'congested' tetrahedron of BrO4- does not prevent the addition of a fifth ligand. In fact, rather than being governed by steric factors, the attachment of O- to oxyanions seems linked to the ability to accommodate an excess electron, a property found in BrO4-, BrO3-, IO3-, and IO4-, which all form O- adducts, but absent in ClO3- and ClO4-, which do not.

The paramagnetic species IO5(2-) is produced from IO4- embedded in KClO4 crystals by thermal addition at room temperature of radiation-induced O-. The observed spin Hamiltonian of IO5(2-) is consistent with a pentacoordinated structure having near-equivalent "normal" I-O bonds to four oxygens and a weaker bond to the fifth oxygen, which holds half of the electron spin density. The mechanism of formation and the geometry of the host lattice indicate that IO5(2-) is a distorted trigonal bipyramid. Photolysis of IO5(2-) produces the paramagnetic complex [O2-,IO3-]. IO5(2-) has an optical absorption with lambda(max) = 530 nm, as have the O-/OH adducts of periodate in aqueous solution reported earlier. Hence the present results are taken to suggest that these adducts, like IO5(2-), are pentacoordinated iodine(VIII) species. The formation of the adducts is reformulated accordingly.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.