Primary branching ratios for the low-temperature reaction of state-prepared N2+ with CH4, C2H2, and C2H4

Product branching ratios (BRs) are reported for ion-molecule reactions of state-prepared nitrogen cation (N(2)(+)) with methane (CH(4)), acetylene (C(2)H(2)). and ethylene (C(2)H(4)) at low temperature using a modified ion imaging apparatus. These reactions are performed in a supersonic nozzle expansion characterized by a rotational temperature of 40 ± 5K. For the N(2)(+) + CH(4) reaction, a BR of 0.83:0.17 is obtained for the dissociative charge-transfer (CT) reaction that gives rise to the formation of CH(3)(+) and CH(2)(+) product ions, respectively. The N(2)(+) + C(2)H(2) ion-molecule reaction proceeds through a nondissociative CT process that results in the sole formation of C(2)H(2)(+) product ions. The reaction of N(2)(+) with C(2)H(4) leads to the formation of C(2)H(3)(+) and C(2)H(2)(+) product ions with a BR of 0.74:0.26, respectively. The reported BR for the N(2)(+) + C(2)H(4) reaction is supportive of a nonresonant dissociative CT mechanism similar to the one that accompanies the N(2)(+) + CH(4) reaction. No dependence of the branching ratios on N(2)(+) rotational level was observed. In addition to providing direct insight into the dynamics of the state-prepared N(2)(+) ion-molecule reactions with the target neutral hydrocarbon molecules, the reported low-temperature BRs are also important for accurate modeling of the nitrogen-dominated upper atmosphere of Saturn's moon, Titan.     

Gas-phase halonium metathesis and its competitors. Skeletal rearrangements of cationic adducts of saturated ketones

The methyl cation and CF(3)(+) attack saturated, acyclic ketones to make vibrationally excited adduct ions. Despite their high internal energies and short lifetimes, these adducts undergo deep-seated rearrangements that parallel slower processes in solution. Observed pathways include alkene and alkane expulsions, in addition to (in the case of CF(3)(+)) the precedented loss of CF(2)O + HF. For the vast majority of ketones, the principal charged products are the CF(3)(+) adducts of lighter carbonyl compounds, ions that are not easily prepared by other avenues. Evidence for ion structures comes from collisionally activated unimolecular decomposition and bimolecular ion-molecule reactions. Typical examples are di-n-propyl and diisopropyl ketones (both of which produce CH(3)CH=OCF(3)(+) as the principal ion-molecule reaction product) and pentamethylacetone (which produces (CH(3))(2)C=OCF(3)(+) as virtually the sole ion-molecule reaction product). Isotopic labeling experiments account for mechanisms, and DFT calculations provide a qualitative explanation for the relative abundances of products from unimolecular decompositions of the chemically activated CF(3)(+) adduct ions that are initially formed.     

Gas phase synthesis, structure and unimolecular reactivity of silver iodide cluster cations, Ag(n)I(m)(+) (n = 2-5, 0 < m < n)

Multistage mass spectrometry (MS(n)) experiments reveal that gas phase silver iodide cluster cations, Ag(n)I(m)(+), are readily built up in a stepwise fashion via ion-molecule reactions between mass selected silver (Ag(3)(+) and Ag(5)(+)) or silver hydride (Ag(2)H(+) and Ag(4)H(+)) cluster cations and allyl iodide, in contrast to their reactions with methyl iodide, which solely result in ligation of the clusters. The stoichiometries of these clusters range from 1 < or = n < or = 5 and 1 < or = m < or = 4, indicating the formation of several new subvalent silver iodide clusters. Collision induced dissociation (CID) experiments were carried out on each of these clusters to shed some light on their possible structures. The products arising from CID of the Ag(n)I(m)(+) clusters are highly dependent on the stoichiometry of the cluster. Thus the odd-electron clusters Ag(4)I(2)(+) and Ag(5)I(+) fragment via loss of a silver atom. In contrast, the even-electron cluster ions all fragment via loss of AgI. In addition, Ag(2)I(2) loss is observed for the Ag(4)I(3)(+) and Ag(5)I(2)(+) clusters, while loss of Ag(3)I(3) occurs for the stoichiometric Ag(5)I(4)(+) cluster. DFT calculations were carried out on these Ag(n)I(m)(+) clusters as well as the neutrals associated with the ion-molecule and CID reactions. A range of different isomeric structures were calculated and their structures are described. A noteworthy aspect is that ligation of these silver clusters by I can have a profound effect on the geometry of the silver cluster. For example, D(3h) Ag(3)(+) becomes C(2v) Ag(3)I(+), which in turn becomes C(2h) Ag(3)I(2)(+). Finally, the DFT predicted thermochemistry supports the different types of reaction channels observed in the ion-molecule reactions and CID experiments.     

Photoproduct channels from BrCD2CD2OH at 193 nm and the HDO + vinyl products from the CD2CD2OH radical intermediate

We present the results of our product branching studies of the OH + C(2)D(4) reaction, beginning at the CD(2)CD(2)OH radical intermediate of the reaction, which is generated by the photodissociation of the precursor molecule BrCD(2)CD(2)OH at 193 nm. Using a crossed laser-molecular beam scattering apparatus with tunable photoionization detection, and a velocity map imaging apparatus with VUV photoionization, we detect the products of the major primary photodissociation channel (Br and CD(2)CD(2)OH), and of the secondary dissociation of vibrationally excited CD(2)CD(2)OH radicals (OH, C(2)D(4)/CD(2)O, C(2)D(3), CD(2)H, and CD(2)CDOH). We also characterize two additional photodissociation channels, which generate HBr + CD(2)CD(2)O and DBr + CD(2)CDOH, and measure the branching ratio between the C-Br bond fission, HBr elimination, and DBr elimination primary photodissociation channels as 0.99:0.0064:0.0046. The velocity distribution of the signal at m/e = 30 upon 10.5 eV photoionization allows us to identify the signal from the vinyl (C(2)D(3)) product, assigned to a frustrated dissociation toward OH + ethene followed by D-atom abstraction. The relative amount of vinyl and Br atom signal shows the quantum yield of this HDO + C(2)D(3) product channel is reduced by a factor of 0.77 ± 0.33 from that measured for the undeuterated system. However, because the vibrational energy distribution of the deuterated radicals is lower than that of the undeuterated radicals, the observed reduction in the water + vinyl product quantum yield likely reflects the smaller fraction of radicals that dissociate in the deuterated system, not the effect of quantum tunneling. We compare these results to predictions from statistical transition state theory and prior classical trajectory calculations on the OH + ethene potential energy surface that evidenced a roaming channel to produce water + vinyl products and consider how the branching to the water + vinyl channel might be sensitive to the angular momentum of the β-hydroxyethyl radicals.     

Reaction mechanism of HCN+ + C2H4: a theoretical study

The complex doublet potential energy surface for the ion-molecule reaction of HCN(+) with C(2)H(4) is investigated at the B3LYP/6-311G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels. The initial association between HCN(+) and C(2)H(4) forms three energy-rich addition intermediates, 1 (HCNCH(2)CH(2)(+)), 2 (HC-cNCH(2)CH(2)(+)), and 3 (N-cCHCH(2)CH(2)(+)), which are predicted to undergo subsequent isomerization and decomposition steps. A total of nine kinds of dissociation products, including P(1) (HCN + C(2)H(4)(+)), P(2) (HCNCHCH(2)(+) + H), P(3) (NCCH(2) + CH(3)(+)), P(4) (CN + C(2)H(5)(+)), P(5) (NCCHCH(2)(+) + H(2)), P(6) (HNCCHCH(2)(+) + H), P(7) (c-CHCCH(2)N(+) + H(2)), P(8) (c-NHCCH(2)C(+) + H(2)), and P(9) (HNCCCH(+) + H(2) + H), are obtained. Among the nine products, P(1) is the most abundant product. P(2) is the second feasible product but is much less competitive than P(1). P(3), P(4), P(5), and P(6) may have the lowest yields observed. Other products, P(7), P(8), and P(9), may become feasible at high temperature. Because the intermediates and transition states involved in the most favorable pathway all lie below the reactant, the HCN(+) + C(2)H(4) reaction is expected to be rapid, which is confirmed by experiment. The present calculation results may provide a useful guide for understanding the mechanism of HCN(+) toward other unsaturated hydrocarbons.     

Electron-stimulated sputtering of thin amorphous solid water films on Pt(111)

The electron-stimulated sputtering of thin amorphous solid water films deposited on Pt(111) is investigated. The sputtering appears to be dominated by two processes: (1) electron-stimulated desorption of water molecules and (2) electron-stimulated reactions leading to the production of molecular hydrogen and molecular oxygen. The electron-stimulated desorption of water increases monotonically with increasing film thickness. In contrast, the total sputtering--which includes all electron-stimulated reaction channels--is maximized for films of intermediate thickness. The sputtering yield versus thickness indicates that erosion of the film occurs due to reactions at both the water/vacuum interface and the Pt/water interface. Experiments with layered films of D2O and H2O demonstrate significant loss of hydrogen due to reactions at the Pt/water interface. The electron-stimulated sputtering is independent of temperature below approximately 80 K and increases rapidly at higher temperatures.     

Site-dependent electron-stimulated reactions in water films on TiO2(110)

Electron-stimulated reactions in thin [<3 ML (monolayer)] water films adsorbed on TiO(2)(110) are investigated. Irradiation with 100 eV electrons results in electron-stimulated dissociation and electron-stimulated desorption (ESD) of adsorbed water molecules. The molecular water ESD yield increases linearly with water coverage theta for 0< or =theta< or =1 ML and 11 ML, the water ESD yield per additional water molecule adsorbed (i.e., the slope of the ESD yield versus coverage) is 3.5 times larger than for theta<1 ML. In contrast, the number of water molecules dissociated per incident electron increases linearly for theta< or =2 ML without changing slope at theta=1 ML. The total electron-stimulated sputtering rate, as measured by postirradiation temperature programmed desorption of the remaining water, is larger for theta>1 ML due to the increased water ESD for those coverages. The water ESD yields versus electron energy (for 5-50 eV) are qualitatively similar for 1, 2, and 40 ML water films. In each case, the observed ESD threshold is at approximately 10 eV and the yield increases monotonically with increasing electron energy. The results indicate that excitations in the adsorbed water layer are primarily responsible for the ESD in thin water films on TiO(2)(110). Experiments on "isotopically layered" films with D(2)O adsorbed on the Ti(4+) sites (D(2)O(Ti)) and H(2)O adsorbed on the bridging oxygen atoms (H(2)O(BBO)) demonstrate that increasing the water coverage above 1 ML rapidly suppresses the electron-stimulated desorption of D(2)O(Ti) and D atoms, despite the fact that the total water ESD and atomic hydrogen ESD yields increase with increasing coverage. The coverage dependence of the electron-stimulated reactions is probably related to the different bonding geometries for H(2)O(Ti) and H(2)O(BBO) and its influence on the desorption probability of the reaction products.     

Activation of the C-I and C-OH bonds of 2-iodoethanol by gas phase silver cluster cations yields subvalent silver-iodide and -hydroxide cluster cations

The gas phase ion-molecule reactions of silver cluster cations (Ag(n)(+)) and silver hydride cluster cations (Ag(m)H(+)) with 2-iodoethanol have been examined using multistage mass spectrometry experiments in a quadrupole ion trap mass spectrometer. These clusters exhibit size selective reactivity: Ag(2)H(+), Ag(3)(+), and Ag(4)H(+) undergo sequential ligand addition only, while Ag(5)(+) and Ag(6)H(+) also promote both C-I and C-OH bond activation of 2-iodoethanol. Collision induced dissociation (CID) of Ag(5)HIO(+), the product of C-I and C-OH bond activation by Ag(5)(+), yielded Ag(4)OH(+), Ag(4)I(+) and Ag(3)(+), consistent with a structure containing AgI and AgOH moieties. Ag(6)H(+) promotes both C-I and C-OH bond activation of 2-iodoethanol to yield the metathesis product Ag(6)I(+) as well as Ag(6)H(2)IO(+). The metathesis product Ag(6)I(+) also promotes C-I and C-OH bond activation.DFT calculations were carried out to gain insights into the reaction of Ag(5)(+) with ICH(2)CH(2)OH by calculating possible structures and their energies for the following species: (i) initial adducts of Ag(5)(+) and ICH(2)CH(2)OH, (ii) the subsequent Ag(5)HIO(+) product, (iii) CID products of Ag(5)HIO(+). Potential adducts were probed by allowing ICH(2)CH(2)OH to bind in different ways (monodentate through I, monodentate through OH, bidentate) at different sites for two isomers of Ag(5)(+): the global minimum "bowtie" structure, 1, and the higher energy trigonal bipyramidal isomer, 2. The following structural trends emerged: (i) ICH(2)CH(2)OH binds in a monodentate fashion to the silver core with little distortion, (ii) ICH(2)CH(2)OH binds to 1 in a bidentate fashion with some distortion to the silver core, and (iii) ICH(2)CH(2)OH binds to 2 and results in a significant distortion or rearrangement of the silver core. The DFT calculated minimum energy structure of Ag(5)HIO(+) consists of an OH ligated to the face of a distorted trigonal bipyramid with I located at a vertex, while those for both Ag(4)X(+) (X = OH, I) involve AgX bound to a Ag(3)(+) core. The calculations also predict the following: (i) the ion-molecule reaction of Ag(5)(+) and ICH(2)CH(2)OH to yield Ag(5)HIO(+) is exothermic by 34.3 kcal mol(-1), consistent with the fact that this reaction readily occurs under the near thermal experimental conditions, (ii) the lowest energy products for fragmentation of Ag(5)HIO(+) arise from loss of AgI, consistent with this being the major pathway in the CID experiments.     

Metastable decomposition and hydrogen migration of ethane dication produced in an intense femtosecond near-infrared laser field

We investigated a formation channel of triatomic molecular hydrogen ions from ethane dication induced by irradiation of intense laser fields (800 nm, 100 fs, ～1 × 10(14) W∕cm(2)) by using time of flight mass spectrometry. Hydrogen ion and molecular hydrogen ion (H,D)(n)(+) (n = 1-3) ejected from ethane dications, produced by double ionization of three types of samples, CH(3)CH(3), CD(3)CD(3), and CH(3)CD(3), were measured. All fragments were found to comprise components with a kinetic energy of ～3.5 eV originating from a two-body Coulomb explosion of ethane dications. Based on the signal intensities and the anisotropy of the ejection direction with respect to the laser polarization direction, the branching ratios, H(+):D(+) = 66:34, H(2)(+):HD(+):D(2)(+) = 63:6:31, and H(3)(+):H(2)D(+):HD(2)(+):D(3)(+) = 26:31:34:9 for the decomposition of C(2)H(3)D(3)(2+), were determined. The ratio of hydrogen molecules, H(2):HD:D(2) = 31:48:21, was also estimated from the signal intensities of the counter ion C(2)(H,D)(4)(2+). The similarity in the extent of H∕D mixture in (H,D)(3)(+) with that of (H,D)(2) suggests that these two dissociation channels have a common precursor with the C(2)H(4)(2+)...H(2) complex structure, as proposed theoretically in the case of H(3)(+) ejection from allene dication [A. M. Mebel and A. D. Bandrauk, J. Chem. Phys. 129, 224311 (2008)]. In contrast, the (H,D)(2)(+) ejection path with a lower extent of H∕D mixture and a large anisotropy is expected to proceed essentially via a different path with a much rapid decomposition rate. For the Coulomb explosion path of C-C bond breaking, the yield ratios of two channels, CH(3)CD(3)(2+)→ CH(3)(+) + CD(3)(+) and CH(2)D(+) + CHD(2)(+), were 81:19 and 92:8 for the perpendicular and parallel directions, respectively. This indicates that the process occurs at a rapid rate, which is comparable to hydrogen migration through the C-C bond, resulting in smaller anisotropy for the latter channel that needs H∕D exchange.     

Isotope effects on the unimolecular dissociation of ionized 3-methyl-2-butanol: reactions via a long-lived C-H-C hydrogen-bridged ion-neutral complex

A pronounced isotope effect causes metastable CD3CHOHCH(CH3)2+* ions to expell C3H6D2 in preference to C3H7D in a ratio of approximately 33:1; a number of related compounds show similar effects. High-level ab initio calculations suggest that the reactant alcohol molecular ion possesses an extraordinarily long alpha-carbon-carbon bond and that the reaction proceeds via the formation of an intermediate hydrogen-bridged complex of propane and ionized vinyl alcohol, in which the bridging hydrogen atom is almost midway between the two carbon termini. The isotopic preference reflects the difference between the zero-point vibrational energies of the isotopically different product pairs rather than kinetic isotope effects on the hydrogen atom transfer reactions that precede dissociation.     

C2H3Cl分子团簇内部离子-分子反应产生C4H5Cl+的研究

用同步辐射对（Ｃ２Ｈ３Ｃｌ）２分子团簇进行了光电离研究，发现该团簇内部发生了离子－分子化学反应，生成了十分稳定的反应产物Ｃ４Ｈ５Ｃｌ＾＋，不再是ｖａｒｄｅｒＷａａｌｓ弱键络合物，本文对反主尖机理进行了初步探讨。     

Guided-ion beam and theoretical study of the potential energy surface for activation of methane by W+

A guided-ion beam tandem mass spectrometer is used to study the reactions, W(+) + CH(4) (CD(4)) and [W,C,2H](+) + H(2) (D(2)), to probe the [W,C,4H](+) potential energy surface. The reaction W(+) + CH(4) produces [W,C,2H](+) in the only low-energy process. The analogous reaction in the CD(4) system exhibits a cross section with strong differences at the lowest energies caused by zero-point energy differences, demonstrating that this reaction is slightly exothermic for CH(4) and slightly endothermic for CD(4). The [W,C,2H](+) product ion reacts further at thermal energies with CH(4) to produce W(CH(2))(x)(+) (x = 2-4). At higher energies, the W(+) + CH(4) reaction forms WH(+) as the dominant ionic product with smaller amounts of WCH(3)(+), WCH(+), and WC(+) also formed. The energy dependent cross sections for endothermic formation of the various products are analyzed and allow the determination of D(0)(W(+)-CH(3)) approximately 2.31 +/- 0.10 eV, D(0)(W(+)-CH(2)) = 4.74 +/- 0.03 eV, D(0)(W(+)-CH) = 6.01 +/- 0.28 eV, and D(0)(W(+)-C) = 4.96 +/- 0.22 eV. We also examine the reverse reaction, [W,C,2H](+) + H(2) (D(2)) --> W(+) + CH(4) (CH(2)D(2)). Combining the cross sections for the forward and reverse processes yields an equilibrium constant from which D(0)(W(+)-CH(2)) = 4.72 +/- 0.04 eV is derived. Theoretical calculations performed at the B3LYP/HW+/6-311++G(3df,3p) level yield thermochemistry in reasonable agreement with experiment. These calculations help identify the structures and electronic states of the species involved and characterize the potential energy surface for the [W,C,4H](+) system.     

环丙烷衍生物在D2O离子体系中的H/D交换反应

在D2O化学反应气条件下研究了环丙烷衍生物的H/D交换反应特性.发现了三种新的产物离子[M+1]+、[M+2]+和[M+3]+.应用碰撞诱导碎裂(CID)技术研究了这些离子的碎裂反应特性.实验结果表明三种新的产物离子是由反应物与试剂离子之间发生H/D交换反应生成的.并获得了环丙烷衍生物结构中活泼氢位置及其数量的信息.     

Ab initio study of C + H3+ reactions

The reaction C + H3+ --> CH(+) + H2 is frequently used in models of dense interstellar cloud chemistry with the assumption that it is fast, i.e. there are no potential energy barriers inhibiting it. Ab initio molecular orbital study of the triplet CH3+ potential energy surface (triplet because the reactant carbon atom is a ground state triplet) supports this hypothesis. The reaction product is 3 pi CH+; the reaction is to exothermic even though the product is not in its electronic ground state. No path has been found on the potential energy surface for C + H3+ --> CH2(+) + H reaction.     

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.     

C_2H_3Cl分子团簇内部离子-分子反应产生C_4H_5Cl~ 的研究

用同步辐射对（C2H3Cl）分子团簇进行了光电离研究，发现该团簇内部发生了离子－分子化学反应，生成了十分稳定的反应产物C4H5Cl＋，不再是varderWaals弱键络合物．本文对反应机理进行了初步探讨     

The syntheses of carbocations by use of the noble-gas oxidant, [XeOTeF5][Sb(OTeF5)6]: the syntheses and characterization of the CX3+ (X = Cl, Br, OTeF5) and CBr(OTeF5)2+ cations and theoretical studies of CX3+ and BX3 (X = F, Cl, Br, I, OTeF5)

The CCl(3)(+) and CBr(3)(+) cations have been synthesized by oxidation of a halide ligand of CCl(4) and CBr(4) at -78 degrees C in SO(2)ClF solvent by use of [XeOTeF(5)][Sb(OTeF(5))(6)]. The CBr(3)(+) cation reacts further with BrOTeF(5) to give CBr(OTeF(5))(2)(+), C(OTeF(5))(3)(+), and Br(2). The [XeOTeF(5)][Sb(OTeF(5))(6)] salt was also found to react with BrOTeF(5) in SO(2)ClF solvent at -78 degrees C to give the Br(OTeF(5))(2)(+) cation. The CCl(3)(+), CBr(3)(+), CBr(OTeF(5))(2)(+), C(OTeF(5))(3)(+), and Br(OTeF(5))(2)(+) cations and C(OTeF(5))(4) have been characterized in SO(2)ClF solution by (13)C and/or (19)F NMR spectroscopy at -78 degrees C. The X-ray crystal structures of the CCl(3)(+), CBr(3)(+), and C(OTeF(5))(3)(+) cations have been determined in [CCl(3)][Sb(OTeF(5))(6)], [CBr(3)][Sb(OTeF(5))(6)].SO(2)ClF, and [C(OTeF(5))(3)][Sb(OTeF(5))(6)].3SO(2)ClF at -173 degrees C. The CCl(3)(+) and CBr(3)(+) salts were stable at room temperature, whereas the CBr(n)(OTeF(5))(3-n)(+) salts were stable at 0 degrees C for several hours. The cations were found to be trigonal planar about carbon, with the CCl(3)(+) and CBr(3)(+) cations showing no significant interactions between their carbon atoms and the fluorine atoms of the Sb(OTeF(5))(6)(-) anions. In contrast, the C(OTeF(5))(3)(+) cation interacts with an oxygen of each of two SO(2)ClF molecules by coordination along the three-fold axis of the cation. The solid-state Raman spectra of the Sb(OTeF(5))(6)(-) salts of CCl(3)(+) and CBr(3)(+) have been obtained and assigned with the aid of electronic structure calculations. The CCl(3)(+) cation displays a well-resolved (35)Cl/(37)Cl isotopic pattern for the symmetric CCl(3) stretch. The energy-minimized geometries, natural charges, and natural bond orders of the CCl(3)(+), CBr(3)(+), CI(3)(+), and C(OTeF(5))(3)(+) cations and of the presently unknown CF(3)(+) cation have been calculated using HF and MP2 methods have been compared with those of the isoelectronic BX(3) molecules (X = F, Cl, Br, I, and OTeF(5)). The (13)C and (11)B chemical shifts for CX(3)(+) (X = Cl, Br, I) and BX(3) (X = F, Cl, Br, I) were calculated by the GIAO method, and their trends were assessed in terms of paramagnetic contributions and spin-orbit coupling.     

Reaction of HOD+ with NO2: effects of OD and OH stretching, bending, and collision energy on reactions on the singlet and triplet potential surfaces

Integral cross sections and product recoil velocity distributions were measured for the reaction of HOD(+) with NO(2), in which the HOD(+) reactant was prepared in its ground state and with mode-selective excitation in the 001 (OH stretch), 100 (OD stretch), and 010 (bend) modes. In addition, we measured the 300 K thermal kinetics in a selected ion flow tube reactor and report product branching ratios different from previous measurements. Reaction is found to occur on both the singlet and triplet surfaces with near-unit efficiency. At 300 K, the product branching indicates that triplet → singlet transitions occur in about 60% of triplet-coupled collisions, which we attribute to long interaction times mediated by complexes on the triplet surface. Because the collision times are much shorter in the beam experiments, the product distributions show no signs of such transitions. The dominant product on the singlet surface is charge transfer. Reactions on the triplet surface lead to NO(+), NO(2)H(+), and NO(2)D(+). There is also charge transfer, producing NO(2)(+) (a(3)B(2)); however, this triplet NO(2)(+) mostly predissociates. The NO(2)H(+)/NO(2)D(+) cross sections peak at low collision energies and are insignificant above ~1 eV due to OH/OD loss from the nascent product ions. The effects of HOD(+) vibration are mode-specific. Vibration inhibits charge transfer, with the largest effect from the bend. The NO(2)H(+)/NO(2)D(+) channels are also vibrationally inhibited, and the mode dependence reveals how energy in different reactant modes couples to the internal energy of the product ions.     

Gas-phase ion chemistry in the ternary SiH4-C3H6-NH3 system

The gas-phase ion chemistry of propene-ammonia and silane-propene-ammonia mixtures was studied by ion trap mass spectrometry. As far as the binary mixture is concerned, the effect of different molar ratios of the reactants on the trend of ion species formed was evaluated, the ion-molecule reaction processes were identified and the rate constants for the main processes were measured. The results were compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-ammonia mixture the mechanisms of formation of Si(m)C(n)N(p)H(q)(+) clusters were elucidated and the rate constants of the most important steps were measured. For some species, selected by double isolation (MS/MS), the low abundance of the ions allowed us to determine the reaction paths but not the rate constants. Ternary ions are mainly formed by reactions of Si(m)C(n)H(q)(+) ions with ammonia, whereas a minor contribution comes from reactions of Si(m)N(p)H(q)(+) ions with propene. On the other hand, the C(n)N(p)H(q)(+) ions showed a very low reactivity and no step leading to ternary ion species was identified. The formation of hydrogenated ternary ions with Si, C and N has a basic importance in relation to their possible role as precursors of amorphous silicon carbides doped with nitrogen obtained by deposition from silane-propene-ammonia mixtures properly activated.     

Gas-phase ion-molecule reactions of metal-carbide cations MCn+ (M=Y and La; n=2, 4, and 6) with benzene and cyclohexane investigated by FTICR mass spectrometry and DFT calculations

Yttrium- and lanthanum-carbide cluster cations YC(n)(+) and LaC(n)(+) (n = 2, 4, and 6) are generated by laser ablation of carbonaceous material containing Y(2)O(3) or La(2)O(3). YC(2)(+), YC(4)(+), LaC(2)(+), LaC(4)(+), and LaC(6)(+) are selected to undergo gas-phase ion-molecule reactions with benzene and cyclohexane. The FTICR mass spectrometry study shows that the reactions of YC(2)(+) and LaC(2)(+) with benzene produce three main series of cluster ions. They are in the form of M(C(6)H(4))(C(6)H(6))(n)(+), M(C(8)H(4))(C(6)H(6))(n)(+), and M(C(8)H(6))(C(6)H(6))(m)(+) (M = Y and La; n = 0-3; m = 0-2). For YC(4)(+), LaC(4)(+), and LaC(6)(+), benzene addition products in the form of MC(n)(C(6)H(6))(m)(+) (M = Y and La; n = 4, 6; m = 1, 2) are observed. In the reaction with cyclohexane, all the metal-carbide cluster ions are observed to form metal-benzene complexes M(C(6)H(6))(n)(+) (M = Y and La; n= 1-3). Collision-induced-dissociation experiments were performed on the major reaction product ions, and the different levels of energy required for the fragmentation suggest that both covalent bonding and weak electrostatic interaction exist in these organometallic complexes. Several major product ions were calculated using DFT theory, and their ground-state geometries and energies were obtained.