OOCO+ cation I: characterization of its isomers and lowest electronic states

Accurate ab initio calculations are performed in order to investigate the stable isomers of OOCO+ and its electronic states at both the molecular and asymptotic regions. These calculations are done using large basis sets and configuration interaction methods. Our theoretical computations predict the presence of four stable forms: A global minimum where a weakly bound charge transfer complex (OOOC+) may be found. Few tenths of cm(-1) above in energy, the OOCO+ very weakly bound isomer is predicted. At 1.75 eV above OOCO+, a strongly bound centrosymmetric isomer (c-CO3+) is located. For energies >8 eV, a third isomer of C(2v) symmetry is found where one oxygen is in the center. The one-dimensional potential energy surface cuts of these electronic states reveal the existence of shallow potential wells for OOCO+ and OOOC+ and of deep potential wells for the two other forms, where electronically excited molecules can be formed at least transiently. Finally, the electronic states of each isomer should interact by spin-orbit, vibronic, Renner-Teller, and Jahn-Teller couplings in competition with isomerization processes converting one form to another.     

Ion chemistry of NOO+

The kinetics for the reactions of NOO+ ions with neutral molecules having ionization potentials (IPs) from 9.27 to 15.58 eV was measured in a selected ion flow tube at 298 K. The NOO+ ions are produced from the reaction of N3+ + O2 and have been reacted with the following: NO, C6F6, CS2, CF3I, C3F6, OCS, C2H6, Xe, SO2, O3, N2O, CO2, Kr, CO, D2, and N2. Numerous types of reactions were observed with the various neutral reagents, including production of NO+ (which may involve loss of an O from the ion or addition of O to the neutral reactant, although the two channels could not be distinguished here), charge transfer, isomerization of NOO+ to ONO+, and hydride abstraction. High level theoretical calculations of the structures and energetics of the various isomers, electronic states, and transition states of NOO and NOO+ were performed to better understand the observed reactivity. All neutral species with an IP< or =11.18 eV were observed to react with NOO+ in part by charge transfer. Detailed calculations showed that the recommended adiabatic and vertical IPs of NOO are 10.4 and 11.7 eV, respectively, at the MRCISDQ/AVQZ level of theory. The observed experimental limit for charge transfer of 11.18 eV agreed well with the energetics of the final products obtained from theory if dissociation of the neutral metastable product occurred, i.e., the products were X+ +[O(3P) + NO(2Pi)], where [O(3P)+NO(2Pi)] formed via dissociation of metastable NOO. Charge exchange with neutral reagent X would, therefore, be exothermic if IP(X)<[IPad(NOO)-DeltaE(O+NO)-NOO]= approximately 11.1 eV, where IPad(NOO) is the adiabatic IP. The potential energy surface for the reaction of NOO+ with C2H6 was also calculated, indicating that two pathways for formation of HNO2 + C2H5 (+) exist.     

Reaction mechanism of CO oxidation on Cu(2)O(111): A density functional study

The possible reaction mechanisms for CO oxidation on the perfect Cu(2)O(111) surface have been investigated by performing periodic density functional theoretical calculations. We find that Cu(2)O(111) is able to facilitate the CO oxidation with different mechanisms. Four possible mechanisms are explored (denoted as M(ER1), M(ER2), M(LH1), and M(LH2), respectively): M(ER1) is CO((gas))+O(2(ads))→CO(2(gas)); M(ER2) is CO((gas))+O(2(ads))→CO(3(ads))→O((ads))+CO(2(gas)); M(LH1) refers to CO((ads))+O(2(ads))→O((ads))+CO(2(ads)); and M(LH2) refers to CO((ads))+O(2(ads))→OOCO((ads))→O((ads))+CO(2(ads)). Our transition state calculations clearly reveal that M(ER1) and M(LH2) are both viable; but M(ER1) mechanism preferentially operates, in which only a moderate energy barrier (60.22 kJ/mol) needs to be overcome. When CO oxidation takes place along M(ER2) path, it is facile for CO(3) formation, but is difficult for its decomposition, thereby CO(3) species can stably exist on Cu(2)O(111). Of course, the reaction of CO with lattice O of Cu(2)O(111) is also considered. However, the calculated barrier is 600.00 kJ/mol, which is too large to make the path feasible. So, we believe that on Cu(2)O(111), CO reacts with adsorbed O, rather than lattice O, to form CO(2). This is different from the usual Mars-van Krevene mechanism. The present results enrich our understanding of the catalytic oxidation of CO by copper-based and metal-oxide catalysts.     

Catalytic activity of Pd ensembles over Au(111) surface for CO oxidation: a first-principles study

Employing the first-principles pseudopotential plane-wave methods and nudged-elastic-band simulations, we studied the reaction of CO oxidation on Pd-decorated Au(111) surface. We found that the contiguous Pd ensembles are required for the CO + O(2) reaction. Interestingly, Pd dimer is an active site for the two-step reaction of CO+O(2)→OOCO→CO(2)+O, and a low energy barrier (0.29 eV) is found for the formation of the intermediate metastable state (OOCO) compared to the barrier of 0.69 eV on Pd trimer. Furthermore, the residual atomic O in the CO + O(2) reaction can be removed by another CO on Pd dimer with the barrier of 0.56 eV close to the value of 0.52 eV on Pd monomer via Langmuir-Hinshelwood mechanism. The higher energy barriers (0.96 and 0.64 eV) are also found for the CO + O reaction on Pd trimers. The calculated results indicate Pd dimer is highly reactive for CO oxidation by O(2) via association mechanism on Pd-decorated Au(111) surface.     

A study of the reaction of N+ with O2: experimental quantification of NO+(a 3Sigma+) production (298-500 K) and computational study of the overall reaction pathways

The product branching ratios for NO+(X 1Sigma+) and NO+(a 3Sigma+) produced from the reaction of N+ with O2 have been measured at 298 and 500 K in a selected ion flow tube. Approximately 0.5% of the total products are in NO+(a) at both temperatures, despite the fact that the reaction to form NO+(a) is 0.3 eV exothermic. High-level ab initio calculations of the potential energy surfaces for the N+ + O2 reaction show that the reaction from N+(3P) + O2(3Sigma(g)) reactants starts with an efficient early stage charge transfer to the N(2D) + O2+(X 2Pi) channel, which gives rise to the O2+(X 2Pi) product and, at the same time, serves as the starting point for all of the reaction channels leading to NO+ and O+ products. Pathways to produce NO+(a 3Sigma+) are found to be less favorable than pathways leading to the major product NO+(X 1Sigma+). Production of N(2D) has implications for the concentration of NO in the mesosphere.     

Ab initio potential energy surfaces of the ion-molecule reaction: C2H2 + O+

High level ab initio calculations using complete active space self-consistent field and multi reference single and double excitation configuration interaction methods with cc-pVDZ (correlation consistent polarized valence double zeta) and cc-pVTZ (triple zeta) basis sets have been performed to elucidate the reaction mechanism of the ion-molecule reaction, C2H2(1Sigmag+) + O+(4S), for which collision experiment has been performed by Chiu et al. [J. Chem. Phys. 109, 5300 (1998)]. The minor low-energy process leading to the weak spin-forbidden product C2H2+ (2Piu) + O(1D) has been studied previously and will not be discussed here. The major pathways to form charge-transfer (CT) products, C2H2+ (2Piu) + O(3P) (CT1) and C2H2+ (4A2) + O(3P) (CT2), and the covalently bound intermediates are investigated. The approach of the oxygen atom cation to acetylene goes over an energy barrier TS1 of 29 kcal/mol (relative to the reactant) and adiabatically leads the CT2 product or a weakly bound intermediate Int1 between CT2 products. This transition state TS1 is caused by the avoided crossing between the reactant and CT2 electronic states. As the C-O distance becomes shorter beyond the above intermediate, the C1 reaction pathway is energetically more favorable than the Cs pathway and goes over the second transition state TS2 of a relative energy of 39 kcal/mol. Although this TS connects diabatically to the covalent intermediate Int2, there are many states that interact adiabatically with this diabatic state and these lead to the other charge-transfer product CT1 via either of several nonadiabatic transitions. These findings are consistent with the experiment, in which charge transfer and chemical reaction products are detected above 35 and 39 kcal/mol collision energies, respectively.     

Adsorption of O2 and oxidation of CO at Au nanoparticles supported by TiO2(110)

Density functional theory calculations are performed for the adsorption of O2, coadsorption of CO, and the CO+O2 reaction at the interfacial perimeter of nanoparticles supported by rutile TiO2(110). Both stoichiometric and reduced TiO2 surfaces are considered, with various relative arrangements of the supported Au particles with respect to the substrate vacancies. Rather stable binding configurations are found for the O2 adsorbed either at the trough Ti atoms or leaning against the Au particles. The presence of a supported Au particle strongly stabilizes the adsorption of O2. A sizable electronic charge transfer from the Au to the O2 is found together with a concomitant electronic polarization of the support meaning that the substrate is mediating the charge transfer. The O2 attains two different charge states, with either one or two surplus electrons depending on the precise O2 adsorption site at or in front of the Au particle. From the least charged state, the O2 can react with CO adsorbed at the edge sites of the Au particles leading to the formation of CO2 with very low (approximately 0.15 eV) energy barriers.     

Ab initio potential-energy surfaces of O2(X3Sigmag -, a1Deltag, b1Sigmag +) +O2 (X3Sigmag -, a1Deltag, b1Sigmag +): mechanism of quenching of O2 (a 1Deltag)

Ab initio computational studies were carried out in order to explore the possible mechanisms of quenching of O(2)(a (1)Delta(g)) by O(2)(X (3)Sigma(g) (-)): the self-quenching of O(2)(a (1)Delta(g)) and other energy-transfer processes involving two O(2) molecules. All eighteen states arising from two O(2) molecules in the X (3)Sigma(g) (-), a (1)Delta(g), and b (1)Sigma(g) (+) states are considered. After scans at the state-averaged complete active space self-consistent field method to identify possible regions of crossing between states belonging to different asymptotes, complete active state second-order perturbation theory high-symmetry optimization and low-symmetry scans established that four different minima on the seams of crossing (MSXs), arising between the a+a manifold and the X+b manifold and responsible for self-quenching: O(2)(a (1)Delta(g))+O(2)(a (1)Delta(g))-->O(2)(X (3)Sigma(g) (-))+O(2)(b (1)Sigma(g) (+)), have coplanar C(2h) or C(2v) symmetries and are only 0.45 eV barrier relative to the a+a asymptote and energetically easily accessible. The rate constant for this process was estimated based on the Landau-Zener formalism. The MSXs for quenching of O(2)(a (1)Delta(g)) by the ground state O(2)(X (3)Sigma(g) (-)):O(2)(a (1)Delta(g))+O(2)(X (3)Sigma(g) (-))-->O(2)(X (3)Sigma(g) (-))+O(2)(X (3)Sigma(g) (-)) require higher energies and the process is not likely to be important.     

Competition of electron transfer, dissociation, and bond-forming processes in the reaction of the CO(2)(2+) dication with neutral CO(2)

The bimolecular reactivity of the CO(2)(2+) dication with neutral CO(2) is investigated using triple quadrupole and ion-ion coincidence mass spectrometry. Crucial for product analysis is the use of appropriate isotope labelling in the quadrupole experiments in order to distinguish the different reactive pathways. The main reaction corresponds to single-electron transfer from the neutral reagent to the dication, i.e. CO(2)(2+) + CO(2) --> 2CO(2)(+); this process is exothermic by almost 10 eV, if ground state monocations are formed. Interestingly, the results indicate that the CO(2)(+) ion formed when the dication accepts an electron dissociates far more readily than the CO(2)(+) ion formed from the neutral CO(2) molecule. This differentiation of the two CO(2)(+) products is rationalized by showing that the population of the key dissociative states of the CO(2)(+) monocation will be favoured from the CO(2)(2+) dication rather than from neutral CO(2). In addition, two bond-forming reactions are observed as minor channels, one of which leads to CO(+) and O(2)(+) as ionic products and the other affords a long-lived C(2)O(3)(2+) dication.     

Gas-phase reactions of atomic lanthanide cations with CO2 and CS2: room-temperature kinetics and periodicities in reactivity

Gas-phase reactions of atomic lanthanide cations (excluding Pm+) have been surveyed systematically with CO2 and CS2 using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Observations are reported for reactions with La+, Ce+, Pr+, Nd+, Sm+, Eu+, Gd+, Tb+, Dy+, Ho+, Er+, Tm+, Yb+, and Lu+ at room temperature (295 +/- 2 K) in helium at a total pressure of 0.35 +/- 0.02 Torr. The observed primary reaction channels correspond to X-atom transfer (X = O, S) and CX2 addition. X-atom transfer is the predominant reaction channel with La+, Ce+, Pr+, Nd+, Gd+, Tb+, and Lu+, and CX2 addition occurs with the other lanthanide cations. Competition between these two channels is seen only in the reactions of CS2 with Nd+ and Lu+. Rate coefficient measurements indicate a periodicity in the reaction efficiencies of the early and late lanthanides. With CO2 the observed trends in reactivity across the row and with exothermicity follow trends in the energy required to achieve two unpaired non-f valence electrons by electron promotion within the Ln+ cation that suggest the presence of a kinetic barrier, in a manner much like those observed previously for reactions with isoelectronic N2O. In contrast, no such barrier is evident for S-atom transfer from the valence isolectronic CS2 molecule which proceeds at unit efficiency, and this is attributed to the much higher polarizability of CS2 compared to CO2 and N2O. Up to five CX2 molecules were observed to add sequentially to selected Ln+ and LnX+ cations.     

Elastic and charge transfer processes in H+ + CO collisions

Proton and hydrogen atom time-of-flight spectra in collision energy range of E(trans) = 9.5-30 eV show that the endoergic charge transfer process in the H+ + CO system is almost an order of magnitude less probable than the elastic scattering [G. Niedner-Schatteburg and J. P. Toennies, Adv. Chem. Phys. LXXXII, 553 (1992)]. Ab initio computations at the multireference configuration interaction level have been performed to obtain the ground- and several low-lying excited electronic state potential energy curves in three different molecular orientations namely, H+ approaching the O-end and the C-end (collinear), and H+ approaching the CO molecule in perpendicular configuration with fixed CO internuclear distance. Nonadiabatic coupling terms between the ground electronic state (H+ + CO) and the three low-lying excited electronic states (H + CO+) have been computed and the corresponding diabatic potentials have been obtained. A time-dependent wavepacket dynamics study is modeled first involving only the ground and the first excited states and then involving the ground and the three lowest excited states at the collision energy of 9.5 eV. The overall charge transfer probability have been found to be approximately 20%-30% which is in qualitative agreement with the experimental findings.     

Spin-orbit coupling in O2(upsilon)+O2 collisions: I. Electronic structure calculations on dimer states involving the X 3Sigmag-, a 1Deltag, and b 1Sigmag+ states of O2

The importance of vibrational-to-electronic (V-E) energy transfer mediated by spin-orbit coupling in the collisional removal of O2(X 3Sigmag-,upsilon>or=26) by O2 has been reported in a recent communication [F. Dayou, J. Campos-Martinez, M. I. Hernandez, and R. Hernandez-Lamoneda, J. Chem. Phys. 120, 10355 (2004)]. The present work provides details on the electronic properties of the dimer (O2)2 relevant to the self-relaxation of O2(X 3Sigmag-,upsilon>0) where V-E energy transfer involving the O2(a 1Deltag) and O2(b 1Sigmag+) states is incorporated. Two-dimensional electronic structure calculations based on highly correlated ab initio methods have been carried out for the potential-energy and spin-orbit coupling surfaces associated with the ground singlet and two low-lying excited triplet states of the dimer dissociating into O2(X 3Sigmag-)+O2(X 3Sigmag-), O2(a 1Deltag)+O2(X 3Sigmag-), and O2(b 1Sigmag+)+O2(X 3Sigmag-). The resulting interaction potentials for the two excited triplet states display very similar features along the intermolecular separation, whereas differences arise with the ground singlet state for which the spin-exchange interaction produces a shorter equilibrium distance and higher binding energy. The vibrational dependence is qualitatively similar for the three studied interaction potentials. The spin-orbit coupling between the ground and second excited states is already nonzero in the O2+O2 dissociation limit and keeps its asymptotic value up to relatively short intermolecular separations, where the coupling increases for intramolecular distances close to the equilibrium of the isolated diatom. On the other hand, state mixing between the two excited triplet states leads to a noticeable collision-induced spin-orbit coupling between the ground and first excited states. The results are discussed in terms of specific features of the dimer electronic structure (including a simple four-electron model) and compared with existing theoretical and experimental data. This work gives theoretical insight into the origin of electronic energy-transfer mechanisms in O2+O2 collisions.     

Reduction of O2 to superoxide anion (O2.-) in water by heteropolytungstate cluster-anions

Fundamental information concerning the mechanism of electron transfer from reduced heteropolytungstates (POM(red)) to O2, and the effect of donor-ion charge on reduction of O2 to superoxide anion (O2.-), is obtained using an isostructural series of 1e--reduced donors: alpha-X(n+)W12O40(9-n)-, X(n+) = Al3+, Si4+, P5+. For all three, a single rate expression is observed: -d[POM(red)]/dt = 2k12[POM(red)][O2], where k12 is for the rate-limiting electron transfer from POM(red) to O2. At pH 2 (175 mM ionic strength), k12 increases from 1.4 +/- 0.2 to 8.5 +/- 1 to 24 +/- 2 M-1s-1 as Xn+ is varied from P5+ (3red) to Si4+ (2red) to Al3+ (1red). Variable-pH data (for 1red) and solvent-kinetic isotope (KIE = kH/kD) data (all three ions) indicate that protonated superoxide (HO2.) is formed in two steps--electron transfer, followed by proton transfer (ET-PT mechanism--rather than via simultaneous proton-coupled electron transfer (PCET). Support for an outersphere mechanism is provided by agreement between experimental k12 values and those calculated using the Marcus cross relation. Further evidence is provided by the small variation in k12 observed when Xn+ is changed from P5+ to Si4+ to Al3+, and the driving force for formation of O2.- (aq), which increases as cluster-anion charge becomes more negative, increases by nearly +0.4 V (a decrease of >9 kcal mol-1 in DeltaG degrees ). The weak dependence of k12 on POM reduction potentials reflects the outersphere ET-PT mechanism: as the anions become more negatively charged, the "successor-complex" ion pairs are subject to larger anion-anion repulsions, in the order [(3(ox)3-)(O2.-)]4- < [(2(ox)4-)(O2.-)]5- < [(1(ox)5-)(O2.-)]6-. This reveals an inherent limitation to the use of heteropolytungstate charge and reduction potential to control rates of electron transfer to O2 under turnover conditions in catalysis.     

Carbon-to-carbon identity proton transfer from allene, ketene, ketenimine, and thioketene to their respective conjugate anions in the gas phase. An ab initio study.

Gas-phase acidities of CH2=C=X (X = CH2, NH, O, and S) and barriers for the identity proton transfers (X=C=CH2 + HC triple bond C-X- right harpoon over left harpoon -X-C triple bond CH + CH2=C=X) as well as geometries and charge distributions of CH2=C=X, HC triple bond C-X- and the transition states of the proton transfer were determined by ab initio methods at the MP2/6-311+G(d,p)//MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory. The acidities were also calculated at the CCSD(T)/6-311+G(2df,p) level. A major objective of this study was to examine how the enhanced unsaturation of CH2=C=X compared to that of CH3CH=X may affect acidities, transition state imbalances, and intrinsic barriers of the identity proton transfer. The results show that the acidities are all higher while the barriers are lower than for the corresponding CH3CH=X series. The transition states are all imbalanced but less so than for the reactions of CH3CH=X.     

Base-induced decomposition of alkyl hydroperoxides in the gas phase. Part 3. Kinetics and dynamics in HO- + CH3OOH, C2H5OOH, and tert-C4H9OOH reactions

The E(CO)2 elimination reactions of alkyl hydroperoxides proceed via abstraction of an alpha-hydrogen by a base: X(-) + R(1)R(2)HCOOH --> HX + R(1)R(2)C=O + HO(-). Efficiencies and product distributions for the reactions of the hydroxide anion with methyl, ethyl, and tert-butyl hydroperoxides are studied in the gas phase. On the basis of experiments using three isotopic analogues, HO(-) + CH3OOH, HO(-) + CD3OOH, and H(18)O(-) + CH3OOH, the overall intrinsic reaction efficiency is determined to be 80% or greater. The E(CO)2 decomposition is facile for these methylperoxide reactions, and predominates over competing proton transfer at the hydroperoxide moiety. The CH3CH2OOH reaction displays a similar E(CO)2 reactivity, whereas proton transfer and the formation of HOO(-) are the exclusive pathways observed for (CH3)3COOH, which has no alpha-hydrogen. All results are consistent with the E(CO)2 mechanism, transition state structure, and reaction energy diagrams calculated using the hybrid density functional B3LYP approach. Isotope labeling for HO(-) + CH3OOH also reveals some interaction between H2O and HO(-) within the E(CO)2 product complex [H2O...CH2=O...HO(-)]. There is little evidence, however, for the formation of the most exothermic products H2O + CH2(OH)O(-), which would arise from nucleophilic condensation of CH2=O and HO(-). The results suggest that the product dynamics are not totally statistical but are rather direct after the E(CO)2 transition state. The larger HO(-) + CH3CH2OOH system displays more statistical behavior during complex dissociation.     

A crossed molecular beam imaging study of the O(1D2)+HCl-->OH+Cl(2P J=3/2, 1/2) reaction.

A crossed molecular beam study is presented for the O((1)D(2))+HCl-->OH+Cl((2)P(J)) reaction at the collision energy of 6 kcal mol(-1). State-resolved doubly differential cross sections are obtained for the Cl((2)P(J=3/2) ) and Cl*((2)P(J=1/2) ) products by velocity-map ion imaging. Both products are slightly more forward scattered, which suggests a reaction mechanism without a long-lived intermediate in the ground electronic state. A small fraction (23 %) of the energy release into the translational degree of freedom indicates strong internal excitation of the counterpart OH radical. The contribution of the electronic excited states of O--HCl to the overall reaction is also examined from the doubly differential cross sections.     

Quantum theory of atoms in molecules charge-charge flux-dipole flux models for the infrared intensities of X(2)CY (X = H, F, Cl; Y = O, S) molecules

The molecular dipole moments, their derivatives, and the fundamental IR intensities of the X2CY (X = H, F, Cl; Y = O, S) molecules are determined from QTAIM atomic charges and dipoles and their fluxes at the MP2/6-311++G(3d,3p) level. Root-mean-square errors of +/-0.03 D and +/-1.4 km mol(-1) are found for the molecular dipole moments and fundamental IR intensities calculated using quantum theory of atoms in molecules (QTAIM) parameters when compared with those obtained directly from the MP2/6-311++G(3d,3p) calculations and +/-0.05 D and 51.2 km mol(-1) when compared with the experimental values. Charge (C), charge flux (CF), and dipole flux (DF) contributions are reported for all the normal vibrations of these molecules. A large negative correlation coefficient of -0.83 is calculated between the charge flux and dipole flux contributions and indicates that electronic charge transfer from one side of the molecule to the other during vibrations is accompanied by a relaxation effect with electron density polarization in the opposite direction. The characteristic substituent effect that has been observed for experimental infrared intensity parameters and core electron ionization energies has been applied to the CCFDF/QTAIM parameters of F2CO, Cl2CO, F2CS, and Cl2CS. The individual atomic charge, atomic charge flux, and atomic dipole flux contributions are seen to obey the characteristic substituent effect equation just as accurately as the total dipole moment derivative. The CH, CF, and CCl stretching normal modes of these molecules are shown to have characteristic sets of charge, charge flux, and dipole flux contributions.     

Ligand effects on structures and spectroscopic properties of pyridine-2-aldoxime complexes of Re(CO)3(+): DFT/TDDFT theoretical studies

The series of novel rhenium(I) tricarbonyl mixed-ligand complexes Re(X)(CO)(3)(N^N) (N^N = pyridine-2-aldoxime; X = -Cl, 1; X = -CN, 2; and X = -C≡C, 3) has been investigated theoretically to explore the ligand X effect on their electronic structures and spectroscopic properties. The contribution of the X ligand to the highest occupied molecular orbital (HOMO) and HOMO-1 decreases in the order of 3 > 1 > 2, in line with the π-donating abilities of the X: -C≡C > -Cl > -CN. The reorganization energy (λ) calculations show that 1 and 3 will result in the higher efficiency of organic light-emitting diodes than 2. The lowest-lying absorptions of 1 and 3 can be assigned to the {[d(xz), d(yz)(Re) + π(CO) + π(X)] → [π* (N^N)]} transition with mixing metal-to-ligand, ligand-to-ligand, and X ligand-to-ligand charge transfer (MLCT/LLCT/XLCT) character, whereas this absorption at 354 nm (H-1 → L) of 2 is assigned to {[d(xz), d(yz)(Re) + π(CO) + π(N^N)] → [π* (N^N)]} transition with MLCT/LLCT/ILCT (intraligand charge transfer). Furthermore, the absorptions are red-shifted in the order 2, 1, and 3, with the increase of π-donating abilities of X ligands. The solvent effects cause red shifts of the absorption and emission spectra with decreasing solvent polarity.     

Reaction mechanisms of C2Cl3 + NO2 via nitro and nitrite adducts

The atmospherically and environmentally important reaction of chlorinated vinyl radical with nitrogen dioxide (C 2Cl 3 + NO 2) is investigated by step-scan time-resolved Fourier transform infrared emission spectroscopy and electronic structure calculations. Vibrationally excited products of CO, NO, Cl 2CO, and NO 2 are observed in the IR emission spectra. Geometries of the major intermediates and transition states along the potential energy surface are optimized at the B3LYP/6-311G(d) level, and their energies are refined at the CCSD(T)/6-311+G(d) level. The reaction mechanisms are characterized to be barrierless addition-elimination via nitro (C 2Cl 3-NO 2) and nitrite (C 2Cl 3-ONO) adducts. Four energetically accessible reaction routes are revealed, i.e., the decomposition of the nitrite adduct forming C 2Cl 3O + NO and its sequential dissociation to CO + NO + CCl 3, the elimination of ClNO from the nitrite adduct leading to ClNO + Cl 2CCO, the Cl-atom shift of the nitrite adduct followed by the decomposition to CCl 3CO + NO, and the O-atom shift of the nitro adduct followed by C-C bond cleavage forming ClCNO + Cl 2CO. In competition with these reactive fluxes, the back-decomposition of nitro or nitrite adducts leads to the prompt formation of vibrationally excited NO 2 and the long-lived reaction adducts facilitate the vibrational energy transfer. Moreover, the product channels and mechanisms of the C 2Cl 3 + NO 2 reaction are compared with the C 2H 3 + NO 2 reaction to explore the effect of chlorine substitution. It is found that the two reactions mainly differ in the initial addition preferentially by the N-attack forming nitro adducts (only N-attack is plausible for the C 2H 3 + NO 2 reaction) or the O-attack forming nitrite adducts (O-attack is slightly more favorable and N-attack is also plausible for the C 2Cl 3 + NO 2 reaction). The addition selectivity can be fundamentally correlated to the variation of the charge density of the end carbon atom of the double bond induced by chlorine substitution due to the electron-withdrawing effect of chlorine groups.     

Gas-phase reactions of atomic lanthanide cations with D2O: room-temperature kinetics and periodicity in reactivity.

Reactions of atomic lanthanide cations (excluding Pm+) with D2O have been surveyed in the gas phase using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer to measure rate coefficients and product distributions in He at 0.35+/-0.01 Torr and 295+/-2 K. Primary reaction channels were observed corresponding to O-atom transfer, OD transfer and D2O addition. O-atom transfer is the predominant reaction channel and occurs exclusively with Ce+, Nd+, Sm+, Gd+, Tb+ and Lu+. OD transfer is observed exclusively with Yb+, and competes with O-atom transfer in the reactions with La+ and Pr+. Slow D2O addition is observed with early lanthanide cation Eu+ and the late lanthanide cations Dy+, Ho+, Er+ and Tm+. Higher-order sequential D2O addition of up to five D2O molecules is observed with LnO+ and LnOD+. A delay of more than 50 kcal mol(-1) is observed in the onset of efficient exothermic O-atom transfer, which suggests the presence of kinetic barriers of perhaps this magnitude in the exothermic O-atom transfer reactions of Dy+, Ho+, Er) and Tm+ with D2O. The reaction efficiency for O-atom transfer is seen to decrease as the energy required to promote an electron to make two non-f electrons available for bonding increases. The periodic trend in reaction efficiency along the lanthanide series matches the periodic trend in the electron-promotion energy required to achieve a d1s1 or d2 excited electronic configuration in the lanthanide cation, and also the periodic trends across the lanthanide row reported previously for several alcohols and phenol. An Arrhenius-like correlation is also observed for the dependence of D2O reactivity on promotion energy for early lanthanide cations, and exhibits a characteristic temperature of 2600 K.