HXeCCH in Ar and Kr matrices

HXeCCH molecule is prepared in Ar and Kr matrices and characterized by IR absorption spectroscopy. The experiments show that HXeCCH can be made in another host than the polarizable Xe environment. The H-Xe stretching absorption of HXeCCH in Ar and Kr is blueshifted from the value measured in solid Xe. The maximum blueshifts are +44.9 and +32.3 cm(-1) in Ar and Kr, respectively, indicating stabilization of the H-Xe bond. HXeCCH has a doublet H-Xe stretching absorption measured in Xe, Kr, and Ar matrices with a splitting of 5.7, 13, and 14 cm(-1), respectively. Ab initio calculations for the 1:1 HXeCCHcdots, three dots, centeredNg complexes (Ng = Ar, Kr, or Xe) are used to analyze the interaction of the hosts with the embedded molecule. These calculations support the matrix-site model where the band splitting observed experimentally is caused by specific interactions of the HXeCCH molecule with noble-gas atoms in certain local morphologies. However, the 1:1 complexation is unable to explain the observed blueshifts of the H-Xe stretching band in Ar and Kr matrices compared to a Xe matrix. More sophisticated computational approach is needed to account in detail the effects of solid environment.     

Fluorine-free organoxenon chemistry: HXeCCH,HXeCC, and HXeCCXeH

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-Ctbd1;C- group without use of XeF(2), which can extend the range of organoxenon compounds.     

Infrared absorption spectrum of matrix-isolated noble-gas hydride molecules: fingerprints of specific interactions and hindered rotation

Noble-gas hydride molecules with the general formula HNgY (Ng denotes noble-gas atom and Y denotes electronegative fragment) are usually prepared in solid noble gases. In many cases, the matrix-isolated HNgY molecules show a characteristic structure of the H-Ng stretching absorption: A close doublet as the main spectral feature and a weaker satellite at higher energy. This characteristic band structure is studied here for matrix-isolated HXeBr and HKrCl molecules. Based on the experimental and theoretical results, we suggest a model explaining the common features of the band structure of the HNgY molecules in noble-gas matrices. In this model, the main doublet bands are attributed to matrix sites where the splitting is caused by specific interactions of the embedded molecule with noble-gas matrix atoms in certain local morphology. The weaker blueshifted band is probably a fingerprint of hindered rotation (libration) of the embedded molecule in the lattice. This librational band has a mirror counterpart at lower energies appearing at higher matrix temperatures. Our present ab initio calculations for the one-to-one Xe...HXeBr complexes and the simulation of hindered rotation in a matrix support this image.     

Matrix isolation and ab initio study of the HXeCCH...CO2 complex

The HXeCCH...CO2 complex is studied experimentally and computationally. The complex is prepared in a low-temperature xenon matrix using UV photolysis of propiolic acid (HCCCOOH) and thermal mobilization of H atoms at 45 K. Photolysis of propiolic acid leads to the HCCH...CO2 complex as one of the photolysis products. The HCCH...CO2 complex is further photolyzed to the HCC...CO2 complex. Thermal annealing leads to the formation of HXeCCH complexed with CO2. The H-Xe stretching absorption of the HXeCCH...CO2 complex is blueshifted (+31.9 and +5.8 cm(-1)) from the value of the HXeCCH monomer in a xenon matrix. In the calculations, three HXeCCH...CO2 structures were found (one parallel and two linear structures) corresponding to the true energy minima on the potential energy surface. For the H-Xe stretching mode, the calculations give blueshifted values of +19.2 or +19.5 cm(-1) depending on the computational level [MP2/6-311++G(2d,2p) and MP2/aug-cc-pVDZ] for the parallel structure and +19.4 or +27.9 cm(-1) for one linear structure. For the second linear structure, the H-Xe stretching frequency is redshifted by -8.6 or -9.4 cm(-1) at these levels of theory. Based on the calculations, the experimental band shifted by +5.8 cm(-1) (1492.2 cm(-1)) most likely corresponds to the HXeCCH...CO2 parallel structure. The band with larger blueshift of +31.9 cm(-1) (1518.3 cm(-1)) can be due to another matrix site of the same structure or to the blueshifting linear structure.     

High kinetic stability of HXeBr upon interaction with carbon dioxide: HXeBr···CO2 complex in a xenon matrix and HXeBr in a carbon dioxide matrix

We investigate the conditions when noble-gas hydrides can be found in real environments and report on the preparation and identification of the HXeBr···CO(2) complex in a xenon matrix and HXeBr in a carbon dioxide matrix. The H-Xe stretching mode of the HXeBr···CO(2) complex in a xenon matrix is observed at 1557 cm(-1), showing a spectral shift of +53 cm(-1) from the HXeBr monomer. The calculations at the CCSD(T)/aug-cc-pVTZ-PP(Xe,Br) level of theory give two stable structures for the HXeBr···CO(2) complex with frequency shifts of +55 and +103 cm(-1), respectively. On the basis of the calculations, the experimentally observed band is assigned to the more stable structure with a "parallel" geometry. The HXeBr molecule was prepared in a carbon dioxide matrix and has the H-Xe stretching frequency of 1646 cm(-1), meaning a strong matrix shift and stabilization of the H-Xe bond. The deuterated species DXeBr in a carbon dioxide matrix absorbs at 1200 cm(-1). This is the first case where a noble-gas hydride is prepared in a molecular solid. The thermal stabilities of HXeBr and HXeBr···CO(2) complex in a xenon matrix and HXeBr in a carbon dioxide matrix were examined. We have found a high thermal stability of HXeBr in carbon dioxide ice (at least up to 100 K), i.e., under conditions that may occur in nature.     

HXeOBr in a xenon matrix

We report on a new noble-gas molecule HXeOBr prepared in a low-temperature xenon matrix from the HBr and N(2)O precursors by UV photolysis and thermal annealing. This molecule is assigned with the help of deuteration experiments and ab initio calculations including anharmonic methods. The H-Xe stretching frequency of HXeOBr is observed at 1634 cm(-1), which is larger by 56 cm(-1) than the frequency of HXeOH identified previously. The experiments show a higher thermal stability of HXeOBr molecules in a xenon matrix compared to HXeOH.     

Experimental evidence for the formation of HXeCCH: the first hydrocarbon with an inserted rare-gas atom

Combined FTIR and EPR studies of acetylene irradiated with fast electrons in a solid xenon matrix provide experimental evidence for the formation of HXeCCH, a novel-type organic molecule with an inserted rare-gas atom. The new species resulting from the reaction of H atoms with CCH radicals in xenon was characterized by an intense IR absorption at 1486.0 cm(-1) corresponding to Xe-H stretching.     

Selective and reversible control of a chemical reaction with narrow-band infrared radiation: HXeCC radical in solid xenon

The light-induced H + XeC2 <--> HXeCC reaction is studied in solid Xe, and the full optical control of this reaction is demonstrated. By narrow-band excitation in the IR spectral region, HXeCC radicals can be decomposed to a local metastable configuration and then selectively recovered by resonant excitation of the XeC2 vibrations. The novel recovery process is explained by short-range mobility of the reagents promoted by vibrational energy redistribution near the absorbing XeC2 molecule. This means that a chemical reaction can be selectively promoted in a desired place where the chosen absorber locates. The obtained results make a strong case of solid-state reactive vibrational excitation spectroscopy of weak radiationless transitions.     

Polarization and experimental configuration analyses of sum frequency generation vibrational spectra, structure, and orientational motion of the air/water interface

Here we report a detailed study on spectroscopy, structure, and orientational distribution, as well as orientational motion, of water molecules at the air/water interface, investigated with sum frequency generation vibrational spectroscopy (SFG-VS). Quantitative polarization and experimental configuration analyses of the SFG data in different polarizations with four sets of experimental configurations can shed new light on our present understanding of the air/water interface. Firstly, we concluded that the orientational motion of the interfacial water molecules can only be in a limited angular range, instead of rapidly varying over a broad angular range in the vibrational relaxation time as suggested previously. Secondly, because different vibrational modes of different molecular species at the interface has different symmetry properties, polarization and symmetry analyses of the SFG-VS spectral features can help the assignment of the SFG-VS spectra peaks to different interfacial species. These analyses concluded that the narrow 3693 cm(-1) and broad 3550 cm(-1) peaks belong to C(infinityv) symmetry, while the broad 3250 and 3450 cm(-1) peaks belong to the symmetric stretching modes with C2v symmetry. Thus, the 3693 cm(-1) peak is assigned to the free OH, the 3550 cm(-1) peak is assigned to the singly hydrogen-bonded OH stretching mode, and the 3250 and 3450 cm(-1) peaks are assigned to interfacial water molecules as two hydrogen donors for hydrogen bonding (with C2v symmetry), respectively. Thirdly, analysis of the SFG-VS spectra concluded that the singly hydrogen-bonded water molecules at the air/water interface have their dipole vector directed almost parallel to the interface and is with a very narrow orientational distribution. The doubly hydrogen-bonded donor water molecules have their dipole vector pointing away from the liquid phase.     

Theoretical study of HKrOX (X = F, Cl, Br and I): structure, anharmonic vibrational spectroscopy, stability and bonding

The noble-gas molecules, HKrOX (with X = F, Cl, Br and I), have been investigated by ab initio calculation. Equilibrium geometry, harmonic and anharmonic vibrational frequencies, energies, partial charges are calculated. All HKrOX molecules studied here are bound equilibrium structures with Cs symmetry. The frequency calculation indicates that the H-Kr stretching mode is anharmonic and is very likely to be observed in the experiments. The two-body decomposition reaction is exothermic and lead to products of Kr as well as HOX, while the three-body decomposition reaction is also exothermic with respect to the neutral decomposition products (H + Kr + OX). Moreover, HKrOX is kinetically stable with respect to the decomposition reactions due to the enough high energy barriers, which indicates the possibility to identify these HKrOX compounds in noble-gas matrices. The bonding in HKrOX is studied by QTAIM analysis and the localized molecular orbital energy decomposition analysis (LMO-EDA) method at the MP2 level of theory with a large basis set. The results show that HKrOX is a typical ionic bond, denoted as (HKr)(+)(OX)(-), and the electrostatic interaction between (HKr)(+) and (OX)(-) makes the main contribution to the ionic bond.     

Theoretical study of the molecular structure and normal coordinate analysis of hydrogen cyanide addition compound with boron trifluoride, HCN-BF(3)

An extensive HF, MP2, B3LYP and CCSD study of the molecular structure and normal vibrations have been performed for the HCN-BF(3) molecule. Calculations with a wide range of basis sets were classified into two groups based on the optimized N-B bond distance. The results for Group A are compared with the experimental structure of the solid phase molecules. The N-B lengths of Group A are approximately linear related to the N-B-F valence angles and also to the N-B stretching frequencies. HF/DZV calculation was used to represent the solid phase model. The N-B lengths of Group B are close to those of the gas phase molecule and both N-B-F angles and N-B sensitive frequencies have roughly the same values. Differences in the chemical bond between gaseous and solid phase HCN-BF(3) are discussed based on the calculated force constants, vibrational frequencies and potential energy distributions. Vibration mode analysis indicates that the nu(4) mode in the 600-700 cm(-1) region can be assigned to the BF(3) symmetric deformation, which shifts upon (10)B/(11)B isotopic substitution. The nu(5) mode which is insensitive to isotope substitution and changes band position with the N-B distance is assigned to the N-B bond stretching vibration.     

Stability of noble-gas hydrocarbons in an organic liquid-like environment: HXeCCH in acetylene

Noble-gas hydrides such as HXeCCH are prepared in cryogenic noble-gas matrices where they are stable. Molecular dynamics simulations reported here predict that HXeCCH is chemically stable in clusters of acetylene, and that stability prevails for temperatures of at least 150 K, at which the clusters are liquid-like. The HXeCCH(C(2)H(2))(n) clusters are studied for sizes up to n = 7. Ab Initio Molecular Dynamics trajectories of 10 ps duration are computed using BLYP-D DFT potential. The liquid-like nature of the system at 150 K is reflected in large amplitude motion of intermolecular distances and orientations. In addition, structures, energetics, NBO charges and bonding analysis at equilibrium are also reported. Complexation is found to be energetically favorable, and to increase the stability of the HXeCCH molecule. The significance of the existence of stable liquid-like complexes of noble-gas hydrides is discussed.     

A combined theoretical and experimental study of the reaction products of laser-ablated thorium atoms with CO: first identification of the CThO, CThO(-), OthCCO, OTh(eta(3)-CCO), and Th(CO)(n) (n = 1-6) molecules

Laser-ablated thorium atoms have been reacted with CO molecules during condensation in excess neon. Absorptions at 617.7 and 812.2 cm(-1) are assigned to Th-C and Th-O stretching vibrations of the CThO molecule. Absorptions at 2048.6, 1353.6, and 822.5 cm(-1) are assigned to the OThCCO molecule, which is formed by CO addition to CThO and photochemical rearrangement of Th(CO)(2). The OThCCO molecule undergoes further photoinduced rearrangement to OTh(eta(3)-CCO), which is characterized by C-C, C-O, and Th-O stretching vibrations at 1810.8, 1139.2, and 831.6 cm(-1). The Th(CO)(n) (n = 1-6) complexes are formed on deposition or on annealing. Evidence is also presented for the CThO(-) and Th(CO)(2)(-) anions, which are formed by electron capture of neutral molecules. Relativistic density functional theory (DFT) calculations of the geometry structures, vibrational frequencies, and infrared intensities strongly support the experimental assignments. It is found that CThO is an unprecedented actinide-containing carbene molecule with a triplet ground state and an unusual bent structure ( angleCThO = 109 degrees ). The OThCCO molecule has a bent structure while its rearranged product OTh(eta(3)-CCO) is found to have a unique exocyclic structure with side-bonded CCO group. We also find that both Th(CO)(2) and Th(CO)(2)(-) are, surprisingly, highly bent, with the angleC-Th-C bond angle being close to 50 degrees; the unusual geometries are the result of extremely strong Th-to-CO back-bonding, which causes significant three-centered bonding among the Th atom and the two C atoms.     

Infrared absorption and electron paramagnetic resonance studies of vinyl radical in noble-gas matrices

Vinyl radicals produced by annealing-induced reaction of mobilized hydrogen atoms with acetylene molecules in solid noble-gas matrices (Ar, Kr, and Xe) were characterized by Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The hydrogen atoms were generated from acetylene by UV photolysis or fast electron irradiation. Two vibrational modes of the vinyl radical (nu7 and nu5) were assigned in IR absorption studies. The assignment is based on data for various isotopic substitutions (D and 13C) and confirmed by comparison with the EPR measurements and density-functional theory calculations. The data on the nu7 mode is in agreement with previous experimental and theoretical results whereas the nu5 frequency agrees well with the computational data but conflicts with the gas-phase IR emission results.     

Experimental and computational study of HXeY...HX complexes (X, Y = Cl and Br): an example of exceptionally large complexation effect

The complexes of xenon hydrides HXeY (Y = Cl and Br) with hydrogen halides HX (X = Cl and Br) have been studied both computationally and experimentally in a xenon matrix. The experiments revealed three new complexes: HXeBr...HBr, HXeBr...HCl, and HXeCl...HCl. The experimental assignments were done on the basis of the strong H-Xe stretching absorption of HXeY (Y = Cl and Br) molecules and supported by theoretical results. We experimentally obtained monomer-to-complex blue-shifts of this vibrational mode for all the studied systems (up to approximately 150 cm (-1)). The electronic structure calculations revealed three local structures for each HNgY...HX complexes and their computed interaction energies varied between -460 and -2800 cm (-1). The computational estimates of the vibrational shifts were in agreement with the experimental values. We also found possible experimental absorption belonging to HXeBr...(HBr) 2 trimer and its vibrational shift (+245 cm (-1)) is similar to the computational estimate of a cyclic ternary complex (+252 cm (-1)).     

Vibrational behavior of adsorbed CO2 on single-walled carbon nanotubes

We present theoretical and experimental evidence for CO(2) adsorption on different sites of single walled carbon nanotube (SWNT) bundles. We use local density approximation density functional theory (LDA-DFT) calculations to compute the adsorption energies and vibrational frequencies for CO(2) adsorbed on SWNT bundles. The LDA-DFT calculations give a range of shifts for the asymmetric stretching mode from about -6 to -20 cm(-1) for internally bound CO(2), and a range from -4 to -16 cm(-1) for externally bound CO(2) at low densities. The magnitude of the shift is larger for CO(2) adsorbed parallel to the SWNT surface; various perpendicular configurations yield much smaller theoretical shifts. The asymmetric stretching mode for CO(2) adsorbed in groove sites and interstitial sites exhibits calculated shifts of -22.2 and -23.8 cm(-1), respectively. The calculations show that vibrational mode softening is due to three effects: (1) dynamic image charges in the nanotube; (2) the confining effect of the adsorption potential; (3) dynamic dipole coupling with other adsorbate molecules. Infrared measurements indicate that two families of CO(2) adsorption sites are present. One family, exhibiting a shift of about -20 cm(-1) is assigned to internally bound CO(2) molecules in a parallel configuration. This type of CO(2) is readily displaced by Xe, a test for densely populated adsorbed species, which are expected to be present on the highest adsorption energy sites in the interior of the nanotubes. The second family exhibits a shift of about -7 cm(-1) and the site location and configuration for these species is ambiguous, based on comparison with the theoretical shifts. The population of the internally bound CO(2) may be enhanced by established etching procedures that open the entry ports for adsorption, namely, ozone oxidation followed by annealing in vacuum at 873 K. Xenon displacement experiments indicate that internally bound CO(2) is preferentially displaced relative to the -7 cm(-1) shifted species. The -7 cm(-1) shifted species is assigned to CO(2) adsorbed on the external surface based on results from etching and Xe displacement experiments.     

HXeBr分子的振动频率和离解途径的理论研究

采用MP2和CCSD(T)方法对HXeBr分子的振动光谱进行了理论研究. 计算结果表明, 经非谐性和基质效应修正后的H—Xe伸缩振动、弯曲振动以及Xe—Br伸缩振动频率分别为1492, 509和174 cm-1, 与实验结果吻合得较好. 此外分别采用单参考组态的CCSD(T)方法和多参考组态耦合簇(MR-AQCC)方法研究了HXeBr分子的稳定性和离解途径. 研究结果表明, 离解途径HXeBr→Xe＋HBr和HXeBr→H＋Xe＋Br的能垒分别为1.39和0.89 eV, 三体离解途径是HXeBr分子的主要离解途径.     

Resonance Raman spectroscopic study of nitrophorin 1, a nitric oxide-binding heme protein from Rhodnius prolixus, and its nitrosyl and cyano adducts.

The resonance Raman (RR) spectra of nitrophorin 1 (NP1) from the saliva of the blood-sucking insect Rhodnius prolixus, in the absence and presence of nitric oxide (NO) and in the presence of cyanide (CN(-)), have been studied. The NP1 displayed RR spectra characteristic of six-coordinate high-spin (6cHS) ferric heme at room temperature and six-coordinate low-spin heme (6cLS) at low temperature (77 K). NO and CN(-) each bind to Fe(III), both ligands forming 6cLS complexes with NP1. The Fe(III)-NO stretching and bending vibrational frequencies of nitrosyl NP1 were identified at 591 and 578 cm(-1), respectively, on the basis of 15NO isotope shifts. These frequencies are typical of Fe-NO ferric heme proteins, indicating that the NP1 nitrosyl adduct has typical bond strength. Thus, the small NO release rate displayed by NP1 must be due to other protein interactions. Room and cryogenic temperature (77 K) RR spectroscopy and 13C, 15N, and 13C15N isotope substitutions have been used to determine vibrational mode frequencies associated with the Fe(III)-CN(-) bond for the cyano adducts at 454, 443, 397, and 357 cm(-1). The results were analyzed by normal mode calculations to support the assignment of the modes and to assess the NO and CN(-) binding geometries. The observed isotope shifts for the cyano NP1 are smaller than expected and reveal vibrational coupling of Fe(III)-CN(-) modes with heme modes. We also find that the observed frequencies are consistent with the presence of a nearly linear Fe(III)CN(-) linkage (173 degrees ) coexisting with a population with a bent structure (155 degrees ).     

Raman properties of chlorophyll d, the major pigment of Acaryochloris marina: studies using both Raman spectroscopy and density functional theory

The Raman spectroscopy of purified chlorophyll (Chl) d extracted from Acaryochloris marina has been measured over the wide region of 250-3200 cm(-1) at 77 K following excitation of its Soret band at 488 nm and analyzed with the aid of hybrid density-functional vibrational analyses. A Raman peak specific to Chl d, which arises from the formyl group 3(1) C=O stretching, was clearly observed at 1659 cm(-1) with medium intensity. Peaks due to other C=O stretching vibrations of the 13(1) keto-, 13(3) ester- and 17(3) groups were also observed. Four very strong peaks were observed in the range of 1000-1600 cm(-1), assigned to the CC stretching and mixtures of the CH3 bend and CN stretching. CCC and NCC bending contribute to medium intensity peaks at 986 and 915 cm(-1). Out-of-plane CH bending at Chl d methine sites 10, 5 and 20 contribute to observed peaks at 885, 864 and 853 cm(-1), respectively. A few modes involving the MgN stretching and MgNC bending motions were observed in the very low frequency range. Density functional theory (DFT) calculations have been used to make assignments on the observed Raman spectrum and the DFT results have been found to be in good agreement with the experimental results.