Reactions of Cu+(1S, 3D) with CH3Cl, CH2ClF, CHClF2, and CClF3

Gaseous transport properties of the ground and excited Cr, Co and Ni cations in He: Ab initio study of electronic state chromatography

The electronic state chromatography (ESC) effect allows the differentiation of ions in their ground and metastable states by their gaseous mobilities in the limit of low electrostatic fields. It is investigated here by means of accurate transport calculations with ab initio ion-atom potentials for the Cr, Co and Ni cations in He buffer gas near room temperature. The values for the open-shell ions in degenerate states are shown to be well approximated by using the single isotropic interaction potential. Minimalistic implementation of the multireference configuration interaction (MRCI) method is enough to describe the zero-field transport properties of metastable ions in the 3dm-14s configuration, such as Cr+(a6D), Co+(a5F) and Ni+(4F), due to their weak and almost isotropic interaction with He atom and the low sensitivity of the measured mobilities to the potential well region. By contrast, interactions involving the ions in the ground 3dm states, such as Cr+(a6S), Co+(a3F) and Ni+(2D), are strong and anisotropic; the MRCI potentials poorly describe their transport coefficients. Even the coupled cluster with singles, doubles and non-iterative triples [CCSD(T)] approach taking into account vectorial spin-orbit coupling may not be accurate enough, as shown here for Ni+(2D). The sensitivity of ion mobility and the ESC effect to interaction potentials, similarities in ion-He interactions of the studied ions in distinct configurations, accuracy and possible improvements of the ab initio schemes, and control of the ESC effect by macroscopic parameters are discussed. Extensive sets of improved interaction potentials and transport data are generated.

Near-Thermal Reactions of Au+(1S,3D) and AuX+ with CH3X (X = Br, I): A Combined Experimental and Computational Analysis

Reactions of Au⁺(¹S,³D) and AuX⁺ with CH₃X (X = I and Br) were performed in the gas phase by utilizing a selected-ion drift cell reactor. These experiments were done at room temperature as well as reduced temperature (∼200 K) at a total pressure of 3.5 Torr in helium. Rate coefficients, product sequencing, and branching fractions were obtained for all reactions to evaluate reaction efficiencies and higher-order processes. Reactions of both Au⁺ states proceed with moderate efficiencies as compared to the average dipole orientation model with these neutral substrates. Results from this work revealed that, dependent on the reacting partner, Au⁺(¹S) exhibits, among others, halogen abstraction, HX elimination, and association. By comparison, Au⁺(³D) participates primarily in charge transfer and halogen abstraction. Dependent on the halogen ligand, AuX⁺ ions induce several processes, including association, charge transfer, halogen loss, and halogen substitution. AuI⁺ reacting with CH₃Br resulted in association exclusively, whereas the AuI⁺/CH₃I and AuBr⁺/CH₃Br systems exhibited halogen loss as the dominant process. By contrast, all possible bimolecular pathways occurred in the reaction of AuBr⁺ with CH₃I. Observed products indicate that displacement of bromine by iodine on gold is favored in ionic products, consistent with the thermochemical preference for formation of the Au⁺-I bond. All AuX⁺ reactions proceed at maximum efficiency. Potential energy surfaces calculated at the B3LYP/def2-TZVPP level of theory for the AuX⁺ reactions are in good agreement with the available thermochemistry for these species and with previously calculated structures and energetics. Experimental and computational results are consistent with a mechanism for the AuX⁺/CH₃Y systems where bimolecular products occur either via direct loss of the halogen originally on Au or via a common intermediate resulting from methyl migration in which the Au center is three-coordinate.

Systematic Ligand Effects in the Reactions of Fe+(6D) and FeX+(5Δ) with CF3X (X = Cl, Br, I). Ion Mobility Measurements of FeX+(5Δ) (X = F, Cl, Br, I) in He

The gas phase reactions of Fe⁺(⁶D) and FeX⁺(⁵Δ) with CF₃X (X = Cl, Br, I) were examined using a selected-ion drift cell reactor under near-thermal energetic conditions. All reactions were carried out in a uniform electric field at a total pressure of 3.5 Torr at room temperature. In addition, reduced zero-field mobilities were measured for FeX⁺(⁵Δ) (X = F, Cl, Br, I) in He, yielding values of 14.2 ± 0.4, 13.7 ± 0.3, 13.3 ± 0.2, and 13.0 ± 0.3 cm²·V^-1·s^-1, respectively. Fe⁺(⁶D) reacts slowly with CF₃Cl and CF₃Br, producing an adduct exclusively with the former and FeBr⁺ with the latter. Conversely, Fe⁺(⁶D) exhibits efficient chemistry with CF₃I to yield FeI⁺, FeCF₃⁺, and FeFI⁺ in parallel reactions. Dependent on the halogen, FeX⁺(⁵Δ) reactions display one or more of four different processes: F^- abstraction, X^- abstraction, halogen switching, and association. In general, the presence of the halogen ligand enhances the rate of reaction over that of Fe⁺(⁶D) with the same molecular substrate. With CF₃Cl, this ligand effect is observed to vary systematically with the electron-withdrawing capability of the halogen. This is illustrated by the correlation between reaction efficiency and the charge distribution on FeX⁺(⁵Δ) as determined from DFT calculations. Specific reaction outcomes for the FeX⁺(⁵Δ) reactions lead to upper and lower bounds on XFe-Y bond strengths (X, Y = F, Cl, Br, I) that are generally consistent with one another and with known trends.

State-Specific Reactions of Cu(+)((1)S,(3)D) with SF6 and SF5Cl

State-specific reactions of Cu(+)((1)S,(3)D) were carried out in a selected ion drift cell apparatus with SF6 and SF5Cl. Copper ions were prepared in a glow discharge utilizing Ne as the working gas. Analysis of Cu(+) states using ion mobility mass spectrometry (IMS) indicated the presence of both Cu(+)(3d(10)) and Cu(+)(3d(9)4s(1)) configurations attributable to the (1)S ground and (3)D first excited states of this metal ion, respectively. State-specific product formation in reactions of these ions with the two neutral substrates of interest here was determined using IMS along with both known and calculated energetic requirements for product formation. These experiments indicate that Cu(+)((1)S) associates with both SF6 and SF5Cl; however, the process is approximately four times as efficient with the latter neutral under these conditions. Association is also observed as a minor product between Cu(+)((3)D) and both neutral reactants. Inefficient formation of SF3(+) occurs as the sole bimolecular product from SF6 via Cu(+)((3)D). In contrast, Cu(+)((3)D) reacts with SF5Cl in rapid parallel bimolecular processes yielding SF3(+) and CuCl(+). These results also indicate that CuCl(+) initiates additional higher-order processes which result in SF5(+) and SF4Cl(+). The energetics associated with the formation of SF3(+) suggest that a copper halide neutral byproduct must also be formed, requiring a more complex mechanism than simple dissociative charge-transfer.

State-specific reactions of Cu(+)((1)S,(3)D,(1)D) with the super greenhouse gas SF5CF3

State-specific reactions of the potent greenhouse gas SF5CF3 with Cu(+) were carried out in a selected ion drift cell apparatus. Copper ions were prepared in a glow discharge utilizing Ne as the working gas. Analysis of these ions using ion mobility mass spectrometry (IMS) indicated the presence of both Cu(+)(3d(10)) and Cu(+)(3d(9)4s(1)) configurations. Subsequent analysis indicates that the 3d(10) configuration consists of Cu(+)((1)S) exclusively whereas the 3d(9)4s(1)configuration is composed primarily of Cu(+)((3)D) with small contributions from Cu(+)((1)D). State-specific product formation in reactions of these ions with SF5CF3 was determined using IMS along with the known energetic requirements for product formation. These experiments reveal that Cu(+) excited states initiate fragmentation of SF5CF3 to yield SF2(+), SF3(+), SF5(+), and CF3(+), where SF3(+) represents the largest branching fraction at 90% of the total bimolecular product formation. The energetics associated with the formation of these ions suggest that molecular Cu-containing products must also be formed in all cases, indicating that the governing reaction mechanisms are more complicated than simple dissociative charge transfer. Production of SF2(+) and SF3(+) are shown to proceed via Cu(+)((3)D) and can be rationalized with a two-step mechanism proceeding through the common intermediate SF3CF3(+). Production of CF3(+) can be explained using this same mechanism but is also energetically possible from Cu(+)((1)D) in a more direct process. Energetic requirements indicate that Cu(+)((1)D) is the sole source of SF5(+) with concomitant formation of CuCF3. Cu(+)((1)S) exhibits adduct formation exclusively, but IMS spectra of the resulting Cu(+)·SF5CF3 suggest that as many as three association structures are formed.

Near-thermal reactions of Au(+)(1S,3D) with CH3X (X = F,Cl)

Reactions of Au(+)((1)S) and Au(+)((3)D) with CH(3)F and CH(3)Cl have been carried out in a drift cell in He at a pressure of 3.5 Torr at both room temperature and reduced temperatures in order to explore the influence of the electronic state of the metal on reaction outcomes. State-specific product channels and overall two-body rate constants were identified using electronic state chromatography. These results indicate that Au(+)((1)S) reacts to yield an association product in addition to AuCH(2)(+) in parallel steps with both neutrals. Product distributions for association vs HX elimination were determined to be 79% association/21% HX elimination for X = F and 50% association/50% HX elimination when X = Cl. Reaction of Au(+)((3)D) with CH(3)F also results in HF elimination, which in this case is thought to produce (3)AuCH(2)(+). With CH(3)Cl, Au(+)((3)D) reacts to form AuCH(3)(+) and CH(3)Cl(+) in parallel steps. An additional product channel initiated by Au(+)((3)D) is also observed with both methyl halides, which yields CH(2)X(+) as a higher-order product. Kinetic measurements indicate that the reaction efficiency for both Au(+) states is significantly greater with CH(3)Cl than with CH(3)F. The observed two-body rate constant for depletion of Au(+)((1)S) by CH(3)F represents less than 5% of the limiting rate constant predicted by the average dipole orientation model (ADO) at room temperature and 226 K, whereas CH(3)Cl reacts with Au(+)((1)S) at the ADO limit at both room temperature and 218 K. Rate constants for depletion of Au(+)((3)D) by CH(3)F and CH(3)Cl were measured at 226 and 218 K respectively, and indicate that Au(+)((3)D) is consumed at approximately 2% of the ADO limit by CH(3)F and 69% of the ADO limit by CH(3)Cl. Product formation and overall efficiency for all four reactions are consistent with previous experimental results and available theoretical models.

Theoretical survey of the potential energy surface of methyl nitrite + Cu+ reaction

The gas-phase reaction of methyl nitrite with Cu+ has been investigated using density functional theory. The geometries and energies of all the stationary points involved in the reaction have been investigated at the B3LYP/6-311+G(2df,2pd) level. Seven different structures of the encounter complexes could be formed when Cu+ attacking at different electronegative heteroatoms of trans and cis conformational isomers of methyl nitrite, in which the inner oxygen attacks account for the most stable complexes. Extensive conversions could take place for these complexes converting into each other. Various mechanisms leading to the loss of NO and HNO are analyzed in terms of the topology of the potential energy surface. The reaction proceeds exclusively from the inner oxygen attachments, followed by four different mechanisms, i.e., direct dissociation, direct H abstraction, N-O activation, and C-H activation, where the former two provide direct channels for the respective losses of NO and HNO, the third one accounts for both of the losses, and C-H activation is unlikely to be important due to the energetics.

Ion mobility of ground and excited states of laser-generated transition metal cations

The application of ion mobility to separate the electronic states of first-, second-, and third-row transition metal cations generated by the laser vaporization/ionization (LVI) technique is presented. The mobility measurements for most of the laser-generated transition metal cations reveal the presence of two or three mobility peaks that correspond to ground and excited states of different electronic configurations. The similarity of the measured reduced mobilities for the metal cations generated by LVI, electron impact, and glow discharge ion sources indicates that the same electronic configurations are produced regardless of the ion source. However, in comparison with electron impact of volatile organometallic compounds, the LVI populates fewer excited states due to the thermal nature of the process. Significant contributions to the production and populations of excited states of Ni+, Nb+, and Pt+ cations have been observed in the presence of argon during the LVI process and attributed to the Penning ionization mechanism. The origin of the mobility difference between the ground and the excited states is mainly due to the different interaction with helium. The ratio of the reduced mobilities of the excited and ground states decreases as one goes from the first- to the second- to the third-row transition metal cations. This trend is attributed to the ion size, which increases in the order 6sd(n-1) > 5sd(n-1) > 4sd(n-1). This work helps to understand the mechanisms by which transition metal cations react in the gas phase by identifying the ground and excited states that can be responsible for their reactivity.

Ion mobility studies of electronically excited States of atomic transition metal cations: development of an ion mobility source for guided ion beam experiments

The design of an ion mobility source developed to couple to a guided ion beam tandem mass spectrometer is presented. In these exploratory studies, metal ions are created continuously by electron ionization of the volatile hexacarbonyls of the three group 6 transition metals. These ions are focused into a linear hexapole ion trap, which collects the ions and then creates high intensity pulses of ions, avoiding excessive ion losses resulting from the low duty cycle of pulsed operation. The ion pulses are injected into a six-ring drift cell filled with helium where ions having different electronic configurations can separate because they have different ion mobilities. Such separation is observed for chromium ions and compares favorably with the pioneering work of Kemper and Bowers (J. Phys. Chem.1991, 95, 5134). The results are then extended to Mo(+) and W(+), which also show efficient configuration separation. The source conditions needed for high intensities and good configuration separation are discussed in detail and suggestions for further improvements are also provided.