A kinetic study of the reactions of Fe+ with N2O, N2, O2, CO2 and H2O, and the ligand-switching reactions Fe+.X + Y --> Fe+.Y + X (X = N2, O2, CO2; Y = O2, H2O)

A series of reactions involving Fe(+) ions were studied by the pulsed laser ablation of an iron target, with detection of ions by quadrupole mass spectrometry at the downstream end of a fast flow tube. The reactions of Fe(+) with N(2)O, N(2) and O(2) were studied in order to benchmark this new technique. Extending measurements of the rate coefficient for Fe(+) + N(2)O from 773 K to 185 K shows that the reaction exhibits marked non-Arrhenius behaviour, which appears to be explained by excitation of the N(2)O bending vibrational modes. The recombination of Fe(+) with CO(2) and H(2)O in He was then studied over a range of pressure and temperature. The data were fitted by RRKM theory combined with ab initio quantum calculations on Fe(+).CO(2) and Fe(+).H(2)O, yielding the following results (120-400 K and 0-10(3) Torr). For Fe(+) + CO(2): k(rec,0) = 1.0 x 10(-29) (T/300 K)(-2.31) cm(6) molecule(-2) s(-1); k(rec,infinity) = 8.1 x 10(-10) cm(3) molecule(-1) s(-1). For Fe(+) + H(2)O: k(rec,0) = 5.3 x 10(-29) (T/300 K)(-2.02) cm(6) molecule(-2) s(-1); k(rec,infinity) = 2.1 x 10(-9) (T/300 K)(-0.41) cm(3) molecule(-1) s(-1). The uncertainty in these rate coefficients is determined using a Monte Carlo procedure. A series of exothermic ligand-switching reactions were also studied at 294 K: k(Fe(+).N(2) + O(2)) = (3.17 +/- 0.41) x 10(-10), k(Fe(+).CO(2) + O(2)) = (2.16 +/- 0.35) x 10(-10), k(Fe(+).N(2) + H(2)O) = (1.25 +/- 0.14) x 10(-9) and k(Fe(+).O(2) + H(2)O) = (8.79 +/- 1.30) x 10(-10) cm(3) molecule(-1) s(-1), which are all between 36 and 52% of their theoretical upper limits calculated from long-range capture theory. Finally, the role of these reactions in the chemistry of meteor-ablated iron in the upper atmosphere is discussed. The removal rates of Fe(+) by N(2), O(2), CO(2) and H(2)O at 90 km altitude are approximately 0.1, 0.07, 3 x 10(-4) and 1 x 10(-6) s(-1), respectively. The initially formed Fe(+).N(2) and Fe(+).O(2) are converted into the H(2)O complex at approximately 0.05 s(-1). Fe(+).H(2)O should therefore be the most abundant single-ligand Fe(+) complex in the mesosphere below 90 km.     

A theoretical study of the ion-molecule chemistry of K+.X complexes (X = O, O2, N2, CO2, H2O): implications for the upper atmosphere

High-level ab initio calculations were carried out on a series of K+.X cluster ions (X = O, O2, N2, CO2, H2O) and X.K+.Y ions. Rice-Ramsberger-Kassel-Markus theory was then used to estimate the rate coefficients for a series of recombination and ligand-switching reactions that govern the ion-molecule chemistry of K+ in the upper mesosphere and lower thermosphere. These rate coefficients were then included in an atmospheric model of potassium chemistry. The important result is that K+ forms weakly bound clusters with N2, O2, and O (the major atmospheric species), with binding energies between 10 and 22 kJ mol(-1). Even under atmospheric conditions (200 K and 10(-3) Torr), these cluster dissociate in less than 1 s. This prevents the formation by ligand-switching of the more stable CO2 and H2O clusters, which could then undergo dissociative recombination with electrons to produce K. The result is that K+ ions have a much longer lifetime against neutralization in the upper atmosphere than other metallic ions such as Na+ and Fe+.     

A kinetic study of the reactions of Ca+ ions with O3, O2, N2, CO2 and H2O

The reactions between Ca(+)(4(2)S(1/2)) and O(3), O(2), N(2), CO(2) and H(2)O were studied using two techniques: the pulsed laser photo-dissociation at 193 nm of an organo-calcium vapour, followed by time-resolved laser-induced fluorescence spectroscopy of Ca(+) at 393.37 nm (Ca(+)(4(2)P(3/2)-4(2)S(1/2))); and the pulsed laser ablation at 532 nm of a calcite target in a fast flow tube, followed by mass spectrometric detection of Ca(+). The rate coefficient for the reaction with O(3) is essentially independent of temperature, k(189-312 K) = (3.9 +/- 1.2) x 10(-10) cm(3) molecule(-1) s(-1), and is about 35% of the Langevin capture frequency. One reason for this is that there is a lack of correlation between the reactant and product potential energy surfaces for near coplanar collisions. The recombination reactions of Ca(+) with O(2), CO(2) and H(2)O were found to be in the fall-off region over the experimental pressure range (1-80 Torr). The data were fitted by RRKM theory combined with quantum calculations on CaO(2)(+), Ca(+).CO(2) and Ca(+).H(2)O, yielding the following results with He as third body when extrapolated from 10(-3)-10(3) Torr and a temperature range of 100-1500 K. For Ca(+) + O(2): log(10)(k(rec,0)/cm(6) molecule(-2) s(-1)) = -26.16 - 1.113log(10)T- 0.056log(10)(2)T, k(rec,infinity) = 1.4 x 10(-10) cm(3) molecule(-1) s(-1), F(c) = 0.56. For Ca(+) + CO(2): log(10)(k(rec,0)/ cm(6) molecule(-2) s(-1)) = -27.94 + 2.204log(10)T- 1.124log(10)(2)T, k(rec,infinity) = 3.5 x 10(-11) cm(3) molecule(-1) s(-1), F(c) = 0.60. For Ca(+) + H(2)O: log(10)(k(rec,0)/ cm(6) molecule(-2) s(-1)) = -23.88 - 1.823log(10)T- 0.063log(10)(2)T, k(rec,infinity) = 7.3 x 10(-11)exp(830 J mol(-1)/RT) cm(3) molecule(-1) s(-1), F(c) = 0.50 (F(c) is the broadening factor). A classical trajectory analysis of the Ca(+) + CO(2) reaction is then used to investigate the small high pressure limiting rate coefficient, which is significantly below the Langevin capture frequency. Finally, the implications of these results for calcium chemistry in the mesosphere are discussed.     

PuX2+(X=O,H,N,C)分子离子的势能函数与稳定性

用密度泛函B3LYP方法对PuX2+(X=O,H,N,C)分子离子进行了理论研究,结果表明:PuO2+,PuH2+,PuN2+和PuC2+分子离子能稳定存在,基态电子状态是X5∑-(PuO2+),X8∑-(PuH2+),X4∑+(PuN2+)和X9∑-(PuC2+),势能函数为Murrell-Sorbie势函数,并导出了相应的几何性质,力学性质和光谱数据.     

A method of describing rotation around (Y)C(sp2)-X bonds (X = C,O, Y = C (sp2), O) in molecular mechanics

Institute for Organic and Physical Chemistry, Kola Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 5, pp. 52–56, September–October, 1991.     

Ca+催化的N2O+CO反应机理的理论研究

采用B3LYP/cc-pVTZ理论水平系统研究了Ca+离子催化N2O+CO→N2+CO2反应的微观机理.反应分两步进行:第一步Ca+夺取N2O中的O原子有两条反应通道,其中优势通道为Ca+金属离子与N2O分子中O作用,形成线性分子复合物,活化N2O分子中的N-O键,之后的反应路径为O-N键断裂机理;第二步为CaO+金属...     

Growing multiconfigurational potential energy surfaces with applications to X + H2 (X = C,N,O) reactions

A previously developed method, based on a Shepard interpolation procedure to automatically construct a quantum mechanical potential energy surface (PES), is extended to the construction of multiple potential energy surfaces using multiconfigurational wave functions. These calculations are accomplished with the interface of the PES-building program, GROW, and the GAMESS suite of electronic structure programs. The efficient computation of multiconfigurational self-consistent field surfaces is illustrated with the C + H2, N + H2, and O + H2 reactions.     

A comparative computational study of FKrCCH...Y, FCCKrH...Y, and FCCH...Y complexes (Y = BF, CO, N2, OH2, OH(CH3), O(CH3)2)

The structural and spectroscopic changes in complexes of FCCKrH...Y and FKrCCH...Y (Y = BF, CO, N(2), OH(2), OH(CH(3)), O(CH(3))(2)) were computed at the MP2∕6-31++G(d,p) level of theory and compared with the corresponding properties for FCCH...Y. The computed bond length changes and frequency shifts on complexation were rationalized by comparing with a perturbation model, which gives quantitative agreement with the standard ab initio results. A recently proposed model also gives a reasonable qualitative account of the observed trends in these complexes.     

ChemInform Abstract: Theoretical Study of Mg+—X and [X—Mg—Y]+ Complexes Important in the Chemistry of Ionospheric Magnesium (X,Y: H2O,CO2, N2, O2, and O).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.     

Ab initio studies of H2PXYH molecules (X,Y = O,S)

Ab initio molecular orbital theory is applied to the study of P? O and P? S bonding in the hypervalent phosphinic (H₂POOH), phosphinothioic (H₂POSH), and phosphinodithioic (H₂PSSH) acid molecules. Intramolecular proton exchange reactions are followed using the intrinsic reaction coordinate and Self-Consistent-Field energy localized orbitals. The P? O and PS bonds are characterized via force constants, phosphorus d orbital populations, and localized orbitals and are best described as either normal single bonds or dative bonds augmented by π back donation from the oxygen or sulfur lone pairs. The anions of these acids are also investigated, and they are found to contain only dative bonds to sulfur and oxygen.     

Transition state structure and energetics of the N(2)O + X (X = Cl,Br) reactions

The structural and vibrational properties of the transition state of the N(2)O + X (X = Cl,Br) reactions have been characterized by ab initio methods using density functional theory. We have employed Becke's hybrid functional (B3LYP), and transition state optimizations were performed with 6-31G(d), 6-311G(2d,2p), 6-311+G(3d,2p), and 6-311+G(3df,2p) basis sets. For the chlorine atom reaction the coupled-cluster method (CCSD(T)) with 6-31G(d) basis set was also used. All calculations resulted in transition state structures with a planar cis arrangement of atoms for both reactions. The geometrical parameters of transition states at B3LYP are very similar, and the reaction coordinates involve mainly the breaking of the N-O bond. At CCSD(T)/6-31G(d) level a contribution of the O-Cl forming bond is also observed in the reaction coordinate. In addition, several highly accurate ab initio composite methods of Gaussian-n (G1, G2, G3), their variations (G2(MP2), G3//B3LYP), and complete basis set (CBS-Q, CBS-Q//B3LYP) series of models were applied to compute reaction energetics. All model chemistries predict exothermic reactions. The G3 and G2 methods result in the smallest deviations from experiment, 1.8 and 0 kcal mol(-1), for the enthalpies of reaction for N(2)O reaction with chlorine and bromine, respectively. The G3//B3LYP and G1 methods perform best among the composite methods in predicting energies of the transition state, with a deviation of 1.9 and 3.0 kcal mol(-1), respectively, in the activation energies for the above processes. However, the B3LYP/6-311+G(3df,2p) method gives smaller deviations of 0.4 and -1.0 kcal mol(-1), respectively. The performance of the methodologies applied in predicting transition state energies was analyzed.     

Urea-water-anion Lattices Part 1. Crystal structures of (C2H5)4N+X−·(NH2)2CO·2 H2O (X=Cl,Br, CN), an isomorphous series of layer-type inclusion complexes

The title ternary complexes (1, X=Cl;2, X=Br;3, X=CN) have been prepared and characterized by X-ray crystallography. Crystal data: space groupP2₁/n,Z=4;1,a=7.505(2),b=14.556(4),c=14.453(3) Å, =98.13(2)^o, andR _F=0.088 for 1831 observed MoK data;2,a=7.483(1),b=14.643(6),c=14.443 Å, =98.25(2)^o, andR _F=0.113 for 923 data;3,a=7.490(2),b=14.646(5),c=14.594(5) Å, =98.85(5)^o, andR _F=0.082 for 915 data. In the isomorphous crystal structure of1 and2, ordered (C₂H₅)₄N⁺ cations are sandwiched between puckered layers matching the (020) family of planes, each being constructed from the cross-linking of planar zigzag chains of hydrogen-bonded urea molecules by the water molecules and halide ions. Compound3 has the same structure except that its cyanide group is disordered. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82066 (30 pages).Operated under contract DE-AC02-76CH00016 with the U.S. Department of Energy, Office of Basic Energy Science.     

Theoretical study of the potential energy surfaces of the Van Der Waals H2O-X2+ (X = Cl or Br) complexes

An ab initio study of the interactions between H2O and Cl2+ and H2O and Br2+ has been performed. We present calculations using both the UMP2 level and the UCCSD(T) level of correlation with the aug-cc-pVTZ basis. The aug-cc-pVQZ basis was tested for selected geometries and was found to yield results similar to the smaller basis. For the H2O-Cl2+ cation, a C2v structure has been identified as the minimum, with De = 6500 cm-1 (78 kJ/mol). A low-lying excited state has De = 6000 cm-1 (72 kJ/mol). The adiabatic and vertical ionization energies of the complex are 10.7 and 11.0 eV, compared to the experimental adiabatic value, 11.5 eV, for free chlorine. For the H2O-Br2+ cation, the calculations are more subtle due to second-order Jahn-Teller effects and result in a Cs structure at the minimum, with De = 6300 cm-1 (75 kJ/mol), yielding an adiabatic ionization energy of 9.9 eV compared to the corresponding experimental value, 10.5 eV, for free bromine. The relatively large binding energies give rise to strong normal mode couplings such that the halogen stretching mode becomes mixed with the water bending and other intermolecular modes, resulting in very large frequency shifts. Vertical ionization energies and ion vibrational frequencies also are reported and used to discuss possible experiments to obtain more precise data for each of the complexes.     

(M4H3X)2B2O2: hydrometal complexes (M = Ni, Mg) containing double tetracoordinate planar nonmetal centers (X = C, N)

Geometrical optimizations and electronic structural analyses of the -O(2)B(2)- bridged hydrometal complexes (M(4)H(3)C)(2)B(2)O(2) and (M(4)H(3)N)(2)B(2)O(2)(2+) (M = Ni, Mg) containing double tetracoordinate planar nonmetals (TPN) have been performed using the density functional theory at the B3LYP/6-311+G(d,p) level. Theoretical evidence of the possibility of double TPN centers coexisting in one planar molecule is presented.     

Reaction paths of the [2+2] cycloaddition of X=C=Y molecules (X, Y=S or O or CH2). Ab initio study

The reaction paths of [2+2] cycloaddition of the X=C=Y cumulenes were modeled at the MP2/aug-cc-pVDZ level. Cycloadditions of allene and CO2, CS2, or OCS lead in part to the same four-membered products as dimerizations of either ketene or thioketene or addition of ketene and thioketene, respectively. All the reactions studied are concerted and mostly asynchronous. The majority of the allene cycloadditions studied are endoergic and proceed with much higher activation barriers than do the alternative (thio)ketene additions. In comparison with the energy of the substrates, the four-membered cycles incorporating S-atoms are stabilized more than the analogous structures with O-atoms built into the rings. There are also some products that are thermodynamically disfavored, yet seem to be obtainable thanks to a relatively low barrier of the reaction. The AIM analysis of the electron density distribution in the transition state structures allowed distinguishing pericyclic from pseudopericyclic and nonplanar-pseudopericyclic types of reaction.     

A Theoretical Study of the Ion—Molecule Chemistry of K+×X Complexes (X: O,O2, N2, CO2, H2O): Implications for the Upper Atmosphere.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

A concerted three-body formation X+Y+C2H4 in the photodissociation of CH2XCH2Y (X,Y=Br,Cl) at 193 nm

The photodissociation of CH2XCH2Y (X,Y=Br,Cl) through absorption of 193 nm photons was investigated using product translational spectroscopy. No stable CH2BrCH2 or CH2ClCH2 was detected. The recorded time-of-flight spectra indicate that these internally excited radicals dissociated into Y+C2H4 in a concerted reaction with the first C-X bond rupture. Product anisotropy implies that the overall reaction time for three-body formation is in a fraction of rotational period. According to an asynchronous concerted reaction model, the measured spectra were simulated with product translational energy distributions coupled by asymmetric angular distributions. For the mixed halide, CH2BrCH2Cl, triple products Br+Cl+C2H4 can be originated from the cleavage of either the C-Br bond or the C-Cl bond. The results are discussed and where appropriate, comparisons with previous investigations of the related molecules are included.     

Theoretical study of binding interactions and vibrational Raman spectra of water in hydrogen-bonded anionic complexes: (H2O)n- (n = 2 and 3), H2O...X- (X = F, Cl, Br, and I), and H2O...M- (M = Cu, Ag, and Au)

Binding interactions and Raman spectra of water in hydrogen-bonded anionic complexes have been studied by using the hybrid density functional theory method (B3LYP) and ab initio (MP2) method. In order to explore the influence of hydrogen bond interactions and the anionic effect on the Raman intensities of water, model complexes, such as the negatively charged water clusters ((H2O)n-, n = 2 and 3), the water...halide anions (H2O...X-, X = F, Cl, Br, and I), and the water-metal atom anionic complexes (H2O...M-, M = Cu, Ag, and Au), have been employed in the present calculations. These model complexes contained different types of hydrogen bonds, such as O-H...X-, O-H...M-, O-H...O, and O-H...e-. In particular, the last one is a dipole-bound electron involved in the anionic water clusters. Our results showed that there exists a large enhancement in the off-resonance Raman intensities of both the H-O-H bending mode and the hydrogen-bonded O-H stretching mode, and the enhancement factor is more significant for the former than for the latter. The reasons for these spectral properties can be attributed to the strong polarization effect of the proton acceptors (X-, M-, O, and e-) in these hydrogen-bonded complexes. We proposed that the strong Raman signal of the H-O-H bending mode may be used as a fingerprint to address the local microstructures of water molecules in the chemical and biological systems.