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and Antti Lignell

Bio: and Antti Lignell is an academic researcher from University of Helsinki. The author has an hindex of 1, co-authored 1 publications receiving 153 citations.

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TL;DR: An additional solid-state configuration of HArF with higher thermal stability is reported, which proves that the doublet at ∼2020 cm-1 originates from the * Address correspondence to this author: (e-mail) Leonid.Fi
Abstract: During the past decade a number of HRgY molecules (H ) hydrogen; Rg ) Ar, Kr, Xe; Y ) an electronegative fragment) have been characterized experimentally in rare-gas solids and computationally by using ab initio methods.1,2 These species are formed from neutral fragments,3 and experiments support their intrinsic stability.4 These molecules constitute an important intermediate during UV photolysis of HY molecules in rare-gas hosts demonstrating the locality of the primary photolysis.5 One of the HRgY molecules, HXeI, has recently been observed in Xe clusters.6 A stable Ar-containing molecule, HArF, was identified in an Ar matrix.2 The high-level ab initio calculations on HArF confirmed its intrinsic stability.7,8 An unclear experimental fact on HArF is its decrease upon annealing above 27 K,2 which contradicts the calculated decomposition barrier of 0.33 eV.7 In this communication, we report an additional solid-state configuration of HArF with higher thermal stability. The HF/Ar solid mixtures were studied in a closed-cycle helium cryostat (APD, DE 202A) at temperatures down to 7.5 K. The samples were deposited onto a cold CsI substrate by passing Ar gas (40Ar from AGA and 36Ar from ICON Services) over an HFpyridine polymer (Fluka) at room temperature. Photolysis of HF was performed with a Kr continuum lamp (Opthos) emitting in the 127-160 nm spectral interval. Our HF/Ar matrixes are quite monomeric as indicated by the IR absorption bands at 3962.5 and 3953.8 cm-1.9 HArF molecules are prepared in the following. First, HF is photodissociated, which stabilizes H and F atoms in solid Ar and leads to some formation of HArF. Next, the photolyzed sample is annealed, which mobilizes the atoms and leads to an increase in the HArF concentration below 20 K.2 The formation of HArF molecules is demonstrated by strong absorption bands at 1965.7, 1969.4, 1972.3 (νH-Ar), 686.9 (δH-Ar-F), and 435.7 cm-1 (νAr-F). The H-Ar stretching region is presented in Figure 1 (see the upper spectrum). The observed bands agree well with the calculated values and show proper shifts upon H and Ar isotopic substitutions. Surprisingly, annealing above 27 K destroys all bands listed above, which was tentatively explained by secondary reactions of mobile matrix species with HArF molecules.2 It was not noticed in the original paper on HArF2 that the decrease of “unstable” HArF molecules is accompanied with an increase of other bands in the H-Ar stretching (2016.3 and 2020.8 cm-1) and bending (693.5 and 697.0 cm-1) regions. This central observation of the present work is illustrated by the lower spectrum in Figure 1. A sign of the novel bands is visible already after annealing at 20 K. We suggest that this novel set of bands belong to HArF in a different solid-state configuration. This additional configuration is thermally rather “stable” and the corresponding bands decrease only with evaporation of the sample. The H-Ar stretching doublet shifts to 1494.0 and 1496.9 cm-1 upon deuteration, and to 2018.5 and 2023.1 cm-1 upon 36Ar/40Ar substitution [see Figure 2a], i.e., in accord with the calculations and experiment on “unstable” HArF.2 These observations prove that the doublet at ∼2020 cm-1 originates from the * Address correspondence to this author: (e-mail) Leonid.Khriachtchev@ Helsinki.Fi. (1) Lundell, J.; Khriachtchev, L.; Pettersson, M.; Rasanen, M. Low Temp. Phys. 2000, 26, 680. (2) Khriachtchev, L.; Pettersson, M.; Runeberg, N.; Lundell, J.; Rasanen, M. Nature (London) 2000, 406, 874. (3) Pettersson, M.; Nieminen, J.; Khriachtchev, L.; Rasanen, M. J. Chem. Phys. 1997, 107, 8423. (4) Lorenz, M.; Rasanen, M.; Bondybey, V. E. J. Phys. Chem. A 2000, 104, 3770. (5) Khriachtchev, L.; Pettersson, M.; Lundell, J.; Rasanen, M. J. Chem. Phys. 2001, 114, 7727. (6) Baumfalk, R.; Nahler, N. H.; Buck, U. J. Chem. Phys. 2001, 114, 4755 (7) Runeberg, N.; Pettersson, M.; Khriachtchev, L.; Lundell, J.; Rasanen, M. J. Chem. Phys. 2001, 114, 836. (8) Lundell, L.; Chaban, G. M.; Gerber, R. B. Chem. Phys. Lett. 2000, 331, 308. (9) Anderson, D. T.; Winn, J. S. Chem. Phys. 1994, 189, 171. Figure 1. Formation of stable HArF in solid Ar. The HF/Ar matrix is deposited and photolyzed at 7.5 K and annealed at 20 and 35 K. Annealing above 27 K destroys unstable HArF (on the right) and forms stable HArF (on the left). The spectra are measured at 7.5 K.

162 citations


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TL;DR: The matrix-isolation synthesis of noble-gas hydrides, their spectroscopic and structural properties, and their stabilities are discussed, including the existence of related polymers, aggregates, and even HNgY crystals, and areas that appear promising for further study include the extension of argon chemistry, preparation of new bonds with noble- gas atoms, and studies of radon compounds.
Abstract: Noble-gas chemistry has been undergoing a renaissance in recent years, due in large part to noble-gas hydrides, HNgY, where Ng = noble-gas atom and Y = electronegative fragment. These molecules are exceptional because of their relatively weak bonding and large dipole moments, which lead to strongly enhanced effects of the environment, complexation, and reactions. In this Account, we discuss the matrix-isolation synthesis of noble-gas hydrides, their spectroscopic and structural properties, and their stabilities. This family of species was discovered in 1995 and now has 23 members that are prepared in noble-gas matrices (HXeBr, HKrCl, HXeH, HXeOH, HXeO, etc.). The preparations of the first neutral argon molecule, HArF, and halogen-free organic noble-gas molecules (HXeCCH, HXeCC, HKrCCH, etc.) are important highlights of the field. These molecules are formed by the neutral H + Ng + Y channel. The first addition reaction involving HNgY molecules was HXeCC + Xe + H → HXeCCXeH, and this led to the first hydrid...

235 citations

Journal ArticleDOI
TL;DR: This work demonstrates a new way to activate the H-Ctbd1;C- group without use of XeF(2), which can extend the range of organoxenon compounds.
Abstract: Three novel Xe-containing organic compounds, HXeCCH, HXeCC (open-shell species), and HXeCCXeH, are identified using infrared absorption spectroscopy. They are prepared in a low-temperature Xe matrix using UV photolysis of acetylene and subsequent annealing at 40−45 K. The experimental observations are supported by extensive ab initio calculations. This work demonstrates a new way to activate the H−C⋮C− group without use of XeF2, which can extend the range of organoxenon compounds.

177 citations

Journal ArticleDOI
TL;DR: The reviewed state-of-the-art suggests this field is at an early stage of development with major open questions bearing on the surprising properties of the molecules and on the formation mechanisms, which are part of the challenge for the future.
Abstract: Progress in the study of a new class of chemically bound compounds of noble-gas atoms is reviewed. The focus is on rare-gas molecules of the form HNgY, where Ng is a noble-gas atom and Y is an electronegative group, prepared by photolysis of HY in the rare-gas matrix. Other related types of new molecules of noble-gas atoms are discussed as well. Topics discussed in this review include: (a) The nature of bonding and the energetic stability of the compounds. (b) The vibrational spectroscopy of the molecules, and its role in identification of the species. (c) The mechanism and dynamics of photochemical formation of HNgY in the matrix, and the pathways for thermal and infrared (IR)-induced decomposition. Specifically, attention is given to the issue of "direct" formation following photolysis of HY versus "delayed" formation involving H atom diffusion. (d) Molecules of the lighter rare gases Ar, Ne, and He, focusing on the experimentally prepared HArF and on theoretical predictions suggesting the existence of other molecules. (e) The most-recently discovered photochemically induced insertion compounds of Ng into hydrocarbons, such as HXeCCH. (f) Clusters of HNgY with other molecules. The possible existence of neat aggregates and crystals of HNgY. The reviewed state-of-the-art suggests this field is at an early stage of development with major open questions bearing on the surprising properties of the molecules and on the formation mechanisms. These are part of the challenge for the future.

175 citations

Journal ArticleDOI
TL;DR: It is believed that a series of similar organokrypton molecules can be prepared as computationally demonstrated for HKrC4H andHKrC3H3 and can find practical applications of the krypton catalysis.
Abstract: An organic molecule containing krypton, HKrCCH, is reported. The preparation of HKrCCH includes 193-nm photolysis of H2C2/Kr solid mixtures at 8 K and subsequent thermal mobilization of hydrogen atoms at ≥30 K. The identification is based on infrared absorption spectroscopy and supported by ab initio calculations which show ionic and covalent contributions to the bonding. We believe that a series of similar organokrypton molecules can be prepared as computationally demonstrated for HKrC4H and HKrC3H3. These results feature a generally novel way for activating chemically the H−C⋮C− group, which can find practical applications of the krypton catalysis.

154 citations

Journal ArticleDOI
TL;DR: In this paper, a new krypton-containing compound, HKrF, has been prepared in a low-temperature Kr matrix via VUV photolysis of the HF precursor and posterior thermal mobilization of H and F atoms.
Abstract: A new krypton-containing compound, HKrF, has been prepared in a low-temperature Kr matrix via VUV photolysis of the HF precursor and posterior thermal mobilization of H and F atoms. All three fundamental vibrations have been observed in the FTIR spectra at ∼1950 cm−1 (H–Kr stretch), ∼650 cm−1 (bending), and ∼415 cm−1 (Kr–F stretch). Two distinct sites of HKrF have been identified. The energy difference between the H–Kr stretching vibrations for the two sites is remarkably large (26 cm−1), indicating a strong influence of the environment. In annealing after the photolysis of the precursor, HKrF is formed in two different stages: at 13–16 K from closely trapped H+F pairs and at T>24 K due to more extensive mobility of H and F atoms in the matrix. HKrF in a less stable site decreases at temperatures above 32 K, the other site being stable up to the sublimation temperature of the matrix. The photodecomposition cross section for HKrF has been measured between 193 and 350 nm and compared with the cross sections...

123 citations