Inductively Coupled Plasma/selected-ion Flow Tube Research Articles

Ligation Kinetics as a Probe for Non-Covalent Electrostatic Bonding and Electron Solvation of Alkali and Alkaline Earth Cations with Ammonia.

Mono-ligation kinetics were measured for ammonia reacting with atomic cations in the first two groups of the periodic table (K+, Rb+, Cs+ and Ca+, Sr+, Ba+). Also, mono-ligation energies were computed using density functional theory (DFT) in an attempt to assess the role of non-covalent electrostatic interactions in these chemical reactions. The measurements were performed at room temperature in helium bath gas at 0.35Torr using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients are reported for ammonia addition, the only reaction channel that was observed with all these cations. A systematic decrease in the rate of addition of NH3 was observed for both group 1 and 2 cations going down the periodic table. The computational studies predict a decrease in the adduct binding energy and an increase in the bond separation going down groups 1 and 2 of the periodic table and provide some insight into the role of the extra selectron in the group 2 radical cations in ligand bonding. A correlation is seen between the efficiency of ligation and the binding energy of the adduct ion and attributed to the lifetime of the intermediate encounter complex against back dissociation which is dependent on its well depth. Higher-order additions of ammonia were also observed. Remarkable differences in the extent and kinetics were seen between the group 1 and 2 cations, and these were attributed to the occurrence of ammonia solvation of the extra s electron in the higher-order adducts of the alkaline earth cations.

Ligation kinetics as a probe for relativistic effects in ion chemistry: Gas-phase ligation of late atomic transition metal cations with OCS and CH3Cl at room temperature

The kinetics of ligation with OCS and CH3Cl were measured to assess the role of relativistic effects in these chemical reactions with the three d10s1 transition metal cations Zn+, Cd+ and Hg+ as well as the three d10 coinage cations Cu+, Ag+ and Au+ and the three d9 cations Ni+, Pd+ and Pt+. Measurements were performed at 295K in helium bath gas at 0.35Torr using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients are reported for OCS and CH3Cl ligation of Zn+, Cd+ and Hg+ and for OCS ligation with the adjacent d10 coinage metal cations. A strong rate enhancement is observed for Hg+ and Au+, similar to that we have reported recently for Pt+ and Au+ reacting with other ligands. We attribute this rate enhancement to the enhancement in the Hg+-OCS, Au+-OCS and Hg+-CH3Cl binding energies expected from relativistic effects. Comparisons are made with the measured rates of ligation of the adjacent main group d10s2 atomic metal cations Ga+, In+ and Tl+ with OCS and CH3Cl and which don’t exhibit a relativistic effect. Further comparisons are made with the rates of ligation of Zn+, Cd+ and Hg+ with CH4, CH3F, and D2O that we reported previously and these also exhibit relativistic effects with Hg+. The relativistic effect is obfuscated by electron transfer to Hg+ with NO, NO2, CS2, NH3, C6H6, C6F6 and C5H5N as we measured previously. Ligation with O2, CO, CO2, N2O and SF6, is immeasurably slow, too slow to exhibit a relativistic effect with Hg+ under our experimental conditions. Furthermore, the additional new measurements with OCS and CH3Cl provide examples of the occurrence of bimolecular channels in competition with ligation, such as S atom transfer with OCS and H2 or HCl elimination with CH3Cl. Finally, we compare the maximum computed relativistic contraction of the 6s shell reported for Au with the occurrence of a maximum in the rate coefficient of ligation for the third-row transition metal cations Pt+, Au+ and Hg+.

Ligation kinetics as a probe for relativistic effects: Ligation of atomic coinage metal cations with ammonia

The kinetics for ammonia ligation of the three (d10) transition metal coinage cations Cu+, Ag+ and Au+ were measured in an attempt to assess the role of relativistic effects in reaction kinetics. Measurements of several main-group cations were included for comparison: the alkali (s0) cations K+, Rb+ and Cs+, the alkaline-earth (s1) cations Ca+, Sr+ and Ba+ and the p0 atomic cations Ga+, In+ and Tl+. Measurements were performed at room temperature in helium bath gas at 0.35Torr using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. The atomic cations are produced at ca. 5500K in an ICP source and are allowed to decay radiatively and to thermalize by collisions with argon and helium atoms prior to reaction. Rate coefficients are reported for ammonia addition, the only reaction channel that was observed with all these cations. A strong enhancement in the rate of addition of NH3 to Au+ was observed for the coinage metal cation period in contrast to the continuous decline in rate down the periodic table that was seen for the main group s0, s1 and p0 cations. We attribute this rate enhancement to the enhancement in the Au+-NH3 binding energy expected from relativistic effects. Comparisons are made with the periodic trends that we have reported previously for the rates of ligation of the coinage metal cations with O2, D2O, N2O, CO2, CS2, CH3F and SF6 and that we measured with pyridine. For seven of the nine ligands that were investigated, rate enhancement with Au+ provided an indirect experimental measure of relativistic effects.

Ligation kinetics as a probe for relativistic effects in ion chemistry: Gas-phase ligation of Ni+, Pd+ and Pt+ at room temperature

The kinetics of ammonia ligation for the three d9 transition metal cations Ni+, Pd+ and Pt+ were measured in an attempt to assess the role of relativistic effects in these chemical reactions. Measurements were performed at room temperature in helium bath gas at 0.35Torr using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. The atomic cations are produced at ca. 5500K in an ICP source and are allowed to decay radiatively and to thermalize by collisions with argon and helium atoms prior to reaction. Rate coefficients are reported for ammonia and pyridine addition, the only reaction channel that was observed with these cations. A strong enhancement in the rate of addition of NH3 to Pt+ was observed for these cations similar to the enhancement recently reported for Au+ in the adjacent coinage metal cation period. We attribute this rate enhancement to the enhancement in the Pt+-NH3 binding energy expected from relativistic effects. Comparisons are made with the periodic trends in the rates of ligation of the d9 atomic metal cations that we also measured with pyridine and that we reported previously with O2, D2O, CS2 and SF6. Rate enhancement with Pt+ was observed for five of the six ligands that were investigated in total and this was attributed to the relativistic stability enhancement of the ligated Pt+. Computational studies were performed with Density Functional Theory (DFT) for M+L, with M=Ni, Pd and Pt and L=NH3, that predict an increase in the binding energy De and a decrease in equilibrium bond separation re in going from Pd+L to Pt+L when relativistic effects are included.

ICP-SIFT/MS study of gas-phase reactions of atomic metal cations with pyridine at room temperature: Kinetics and periodicities in reactivity

Chemical reactions of 18 singly-charged atomic metal ions with pyridine were studied in the gas phase at room temperature (295±2K) in helium at a total pressure of 0.35±0.02Torr using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Observations are reported for 4 group I and II main group cations and 14 group III–VII transition metal cations. Addition of up to 5 pyridine molecules is observed with the number added generally decreasing from left to right on the periodic table, from 5 to 3, with the exception of group I cations which add only 2. The number of added pyridine molecules shows a good correlation with the ligand field stabilization energy (LFSE); atomic metal cations with a higher stabilization energy add more pyridine molecules. Some atomic metal cations exhibit pyridine ring cleavage, predominantly by elimination of acetylene, C2H2, with one example of HCN elimination usually observed in pyridine ring cleavage. The reaction efficiency was measured to be high, mostly ≥50%, for both addition and ring cleavage. The exceptions are the group I metal cations for which addition is 10 times slower.

ICP-SIFT/MS study of gas-phase reactions of lanthanide cations with benzene: Room-temperature kinetics and periodicities in reactivity

The gas-phase reactivity of atomic lanthanide cations (excluding Pm+) has been surveyed systematically with benzene using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer with an added facility for collisional dissociation of product ions. Observations are reported with La+, Ce+, Pr+, Nd+, Sm+, Eu+, Gd+, Tb+, Dy+, Ho+, Er+, Tm+, Yb+ and Lu+ at room temperature (295±2K) in helium at a total pressure of 0.35±0.02Torr. All the Ln+ ions were observed to add benzene exclusively and rapidly with efficiencies ≥28%. Sequential addition of C6H6 was seen to saturate with the formation of Ln+(C6H6)3. Measured onset energies were high (>33kcalmol−1) for the dissociation of La+C6H6, Ce+C6H6, Pr+C6H6, Gd+C6H6 and Tb+C6H6 and low (<20 kcalmol−1) for the dissociation of the remaining Ln+C6H6 cations.The reaction efficiency for the formation of Ln+C6H6 and the measured onset of benzene removal from Ln+C6H6 by collisional dissociation were seen to correlate with the electron promotion energy required to achieve a two non-f electron configuration in Ln+. These results are interpreted in terms of schematic triple minimum potential energy profiles in which the electron promotion energy can act as a “gate” for the conversion between an electrostatically bound adduct, an adduct of the sd-hybridized lanthanide cation and one achieved by a CH bond insertion of Ln+. The ICP/SIFT results are compared with results of FT/ICR measurements at low pressure.

Energy transfer from electronically excited atomic platinum cations to hydrogen and deuterium molecules in the gas phase at room temperature

A novel, efficient quenching reaction for excited atomic platinum cations with hydrogen gas has been identified experimentally with an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The rate and extent of quenching is monitored using the state-selective reaction of Pt+ with N2O and the quenching with molecular hydrogen appears to be very efficient at room temperature, the rate coefficient was measured to be approximately 3×10−10cm3molecule−1s−1. For comparative purposes, experiments also were performed with deuterium and nitrogen. The higher mass isotope deuterium appears to be slightly more efficient as a quenching agent than hydrogen, while N2 is completely ineffective as a quenching agent. An inspection of energy resonance as a criterion for collisional quenching to occur, an approach fraught with uncertainty, indicated that such a criterion is hardly useful even with the application of spectroscopic selection rules for rovibrational transitions in the diatomic quench gas. The elucidation of a quenching mechanism involving the formation and dissociation of an inserted, or partially inserted, vibrationally excited intermediate will require full computations of the relevant potential energy surfaces.

Nitrogen Dioxide Reactions with 46 Atomic Main-Group and Transition Metal Cations in the Gas phase: Room Temperature Kinetics and Periodicities in Reactivity

Experimental results are reported for the gas-phase room-temperature kinetics of chemical reactions between nitrogen dioxide (NO(2)) and 46 atomic main-group and transition metal cations (M(+)). Measurements were taken with an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer in helium buffer gas at a pressure of 0.35 ± 0.01 Torr and at 295 ± 2 K. The atomic cations were produced at ca. 5500 K in an ICP source and allowed to decay radiatively and to thermalize to room temperature by collisions with Ar and He atoms prior to reaction with NO(2). Measured apparent bimolecular rate coefficients and primary reaction product distributions are reported for all 46 atomic metal cations and these provide an overview of trends across and down the periodic table. Three main types of reactions were observed: O-atom transfer to form either MO(+) or NO(+), electron transfer to form NO(2)(+), and addition to form MNO(2)(+). Bimolecular O-atom transfer was observed to predominate. Correlations are presented between reaction efficiency and the O-atom affinity of the metal cation and between the prevalence of NO(+) product formation and the electron recombination energy of the product metal oxide cation. Some second-order reactions are evident with metal cations that react inefficiently. Most interesting of these is the formation of the MNO(+) cation with Rh(+) and Pd(+). The higher-order chemistry with NO(2) is very diverse and includes the formation of numerous NO(2) ion clusters and a number of tri- and tetraoxide metal cations. Group 2 metal dioxide cations (CaO(2)(+), SrO(2)(+), BaO(2)(+)) exhibit a unique reaction with NO(2) to form MO(NO)(+) ions perhaps by NO transfer from NO(2) concurrent with O(2) formation by recombination of a NO(2) and an oxide oxygen.

Nitrogen dioxide reactions with atomic lanthanide cations and their monoxides: gas-phase kinetics at room temperature

Results of experimental investigations are reported for the gas-phase kinetics of chemical reactions between nitrogen dioxide (NO(2)) and 14 different atomic cations of the lanthanide series, Ln(+) (Ln = La-Lu, excluding Pm), and their monoxides, LnO(+). Measurements were taken with an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer in helium buffer-gas at a pressure of 0.35 +/- 0.01 Torr and at 295 +/- 2 K. The atomic lanthanide cations were produced at ca. 5500 K in an ICP source and allowed to decay radiatively and to thermalize by collisions with Ar and He atoms prior to reaction with NO(2). The atomic ions were observed to react rapidly with NO(2) with large rate coefficients, k > 2 x 10(-10) cm(3) molecule(-1) s(-1), and almost exclusively by oxygen-atom abstraction to produce lanthanide-oxide LnO(+) cations. In contrast to results of previous studies with many other molecules, the reaction efficiency exhibits essentially no dependence upon the energy required to promote an electron to achieve a d(1)s(1) excited electronic configuration, in which two non-f electrons are available to Ln(+) for chemical bonding. Apparently the radical character of NO(2) (X (2)A(1)) leads to the efficient formation of LnO(+) by the end-on abstraction of an oxygen atom by Ln(+). In the reactions with La(+), Ce(+), Pr(+) and Gd(+) an additional minor channel (less than 2%) leads to the formation of NO(+). The LnO(+) product ions participate in various secondary and higher order reactions with NO(2) resulting in the formation of ions of the type LnO(x)(NO)(y)(NO(2))(z)(+) with x = 1-2, y = 0-2, and z = 0-2, as well as the ions NO(+) and NO(2)(+).

Gas-Phase Reactions of Atomic Lanthanide Cations with Ammonia: Room-Temperature Kinetics and Periodicity in Reactivity

Reactions of (14) atomic lanthanide cations (excluding Pm(+)) with ammonia have been surveyed in the gas phase by 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 H(2) elimination with formation of the protonated lanthanum nitride and NH(3) addition. H(2) elimination was seen only in the reactions with La(+), Ce(+), Gd(+), and Tb(+) and occurs with these ions exclusively. NH(3) addition was seen with Pr(+), Nd(+), Sm(+), Eu(+), Dy(+), Ho(+), Er(+), Tm(+), Yb(+), and Lu(+). Higher-order sequential addition of up to five NH(3) molecules was observed with the Ln(+)(NH(3)) and LnNH(+) ions. The reaction efficiency of the primary reactions 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 quite closely the periodic trend in the electron-promotion energy required to achieve a d(1)s(1) or d(2) excited electronic configuration in the lanthanide cation. With La(+), Ce(+), Gd(+), and Tb(+), the electrostatic attraction between the atomic lanthanide cation and ammonia is sufficiently strong to provide enough energy to achieve electron promotion and to overcome any barriers to subsequent N-H bond insertion and H(2) loss, but this is not the case with the other lanthanide cations with which collisional stabilization of the intermediate adduct ion, with or without insertion of Ln(+), predominates.

Reactions of Atomic Cations with Methane: Gas Phase Room-Temperature Kinetics and Periodicities in Reactivity

Reactions of methane have been measured with 59 atomic metal cations at room temperature in helium bath gas at 0.35 Torr using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The atomic cations were produced at approximately 5500 K in an ICP source and allowed to decay radiatively and to thermalize by collisions with argon and helium atoms prior to reaction. Rate coefficients and product distributions are reported for the reactions of fourth-row atomic cations from K(+) to Se(+), of fifth-row atomic cations from Rb(+) to Te(+) (excluding Tc(+)), of sixth-row atomic cations from Cs(+) to Bi(+), and of the lanthanide cations from La(+) to Lu(+) (excluding Pm(+)). Two primary reaction channels were observed: C-H bond insertion with elimination of H(2), and CH(4) addition. The bimolecular H(2) elimination was observed in the reactions of CH(4) with As(+), Nb(+), and some sixth-row metal cations, i.e., Ta(+), W(+), Os(+), Ir(+), Pt(+); secondary and higher-order H(2) elimination was observed exclusively for Ta(+), W(+), and Ir(+) ions. All other transition-metal cations except Mn(+) and Re(+) were observed to react with CH(4) exclusively by addition, and up to two methane molecules were observed to add sequentially to most transition-metal ions. CH(4) addition was also observed for Ge(+), Se(+), La(+), Ce(+), and Gd(+) ions, while the other main-group and lanthanide cations did not react measurably with methane.

Gas-Phase Reactions of Sulfur Hexafluoride with Transition Metal and Main Group Atomic Cations: Room-Temperature Kinetics and Periodicities in Reactivity

Gas-phase reactions of SF(6) were investigated with 46 different atomic metal and main group cations at room temperature using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. The atomic ions were produced at about 5500 K in the ICP source and allowed to decay radiatively and to thermalize by collisions with argon and helium atoms prior to reaction downstream in a flow tube in helium buffer gas at 0.35 +/- 0.01 Torr and 295 +/- 2 K. Rate coefficients and product distributions were measured for the reactions of fourth-row atomic ions from K(+) to Se(+), of fifth-row atomic ions from Rb(+) to Te(+) (excluding Tc(+)), and of sixth-row atomic ions from Cs(+) to Bi(+). The early transition metal ions react with SF(6) very efficiently (k/k(c) = 0.56-0.96) to produce MF(m)(+) (m = 1-4) and SF(n)(+) (n = 1-4) ions, whereas the late transition metal ions react much less efficiently (k/k(c) < 0.2) to form M(+)(SF(6)) adduct ions. Reactions of SF(6) with Ca(+), Sr(+), Ba(+), Ge(+), and As(+) proceed efficiently (k/k(c) = 0.35-0.85) through various channels, while all other main group metal ions are inert toward sulfur hexafluoride. Primary and secondary adduct formation was observed to exhibit equilibrium kinetics, and the standard free energy change for SF(6) addition is found to correlate with the efficiency of addition according to log[k/k(c)] = -8.7 + 7.8 log[-DeltaG(o)/(kcal mol(-1))]. Several MF(m)(+) ions were observed to react further with SF(6) to produce MF(m+k)(+), SF(n)(+), and MF(m)(+)(SF(6)) as secondary products.

Activation of X–H and X–D bonds (X = O, N, C) by alkaline-earth metal monoxide cations: experiment and theory

Experimental investigations are reported for reactions of MO (+) (M = Ca, Sr, and Ba) with elemental hydrides water, ammonia and methane proceeding in the gas phase at 295 +/- 3 K in helium buffer gas at a pressure of 0.35 +/- 0.01 Torr. Measurements were taken with an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer and a novel electrospray ion source/ion selection quadrupole/selected-ion flow tube/triple quadrupole (ESI/qQ/SIFT/QqQ) mass spectrometer. All three alkaline-earth metal oxide ions exclusively abstract a H-atom from the three hydrides with rate coefficients > 1 x 10(-11) cm(3) molecule(-1) s(-1). Formation of metal hydroxide ion was followed by sequential addition of water or ammonia, but not methane. Density functional calculations have provided potential energy surfaces for the X-H bond activations leading to H-atom abstraction as well as those for O-atom transfer and H(2)O elimination (with ammonia and methane). A comparison of experimental and theoretical isotope effects points toward a mechanism involving the direct atom transfer from XH and XD to O in MO (+)via a three-centered transition structure.

Catalytic Oxidation of H2 by N2O in the Gas Phase: O-Atom Transport with Atomic Metal Cations

Twenty-five atomic cations, M (+), that lie within the thermodynamic window for O-atom transport catalysis of the oxidation of hydrogen by nitrous oxide, have been checked for catalytic activity at room temperature with kinetic measurements using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Only 4 of these 25 atomic cations were seen to be catalytic: Fe (+), Os (+), Ir (+), and Pt (+). Two of these, Ir (+) and Pt (+), are efficient catalysts, while Fe (+) and Os (+) are not. Eighteen atomic cations (Cr (+), Mn (+), Co (+), Ni (+), Cu (+), Ge (+), Se (+), Mo (+), Ru (+), Rh (+), Sn (+), Te (+), Re (+), Pb (+), Bi (+), Eu (+), Tm (+), and Yb (+)) react too slowly at room temperature either in their oxidation with N 2O to form MO (+) or in the reduction of MO (+) by H 2. Many of these reactions are known to be spin forbidden and a few actually may lie outside the thermodynamic window. Three alkaline-earth metal monoxide cations, CaO (+), SrO (+), and BaO (+), were observed to favor MOH (+) formation in their reactions with H 2. A potential-energy landscape is computed for the oxidation of H 2 with N 2O catalyzed by Fe (+)( (6)D) that vividly illustrates the operation of an ionic catalyst and qualitatively accounts for the relative inefficiency of this catalyst.

On the chemical resolution of the 87Rb + (s 0)/ 87Sr + (s 1) isobaric interference: A kinetic search for an optimum reagent

Room-temperature reactions of the atomic cations Sr + and Rb + have been surveyed systematically with a variety of gases using an Inductively-Coupled Plasma/Selected-Ion Flow Tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients and product distributions have been measured in He buffer gas at 0.35 Torr and 295 K for reactions of Sr + and Rb + with CH 3F, CH 3Cl, N 2O, CO 2, CS 2, SF 6, D 2O and NH 3. Rb + (s 0) is seen to be quite inert with these molecules and reacts either slowly by molecule addition or not at all, while Sr + (s 1) is much more reactive with all these 8 molecules, especially with CH 3F, CH 3Cl, N 2O and SF 6. Sr + reacts with CH 3F and SF 6 by F-atom transfer, with CH 3Cl by Cl-atom transfer and with N 2O by O-atom transfer, and the reaction rate coefficients are all quite high, k ≥ 1.4 × 10 −11 cm 3 molecules −1 s −1. The extreme differences in reactivity with CH 3F, SF 6, CH 3Cl and N 2O provide a chemical basis for the separation of isobaric interferences of 87Rb + and 87Sr + often encountered in ICP–MS. Among these four molecules, SF 6 exhibits the largest difference in reactivity, almost a factor of 10 4, and so is identified as the kinetically recommended reagent for the chemical resolution of the isobaric interference of 87Rb + and 87Sr +.

Packing atomic metal cations with C 60: Mass spectrometric observation of M +(C 60) n with M = Sr and Mo and n = 0–4

The atomic cations of Sr and Mo have been observed to add sequentially up to four molecules of C 60 in helium at 0.35 Torr and room temperature in the flow tube of a modified inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The available center-of-mass energy in collision-induced dissociation experiments of approximately 1.3 eV failed to remove C 60 from M +(C 60) 4. A structure is proposed for M +(C 60) 4 cations in which the bonding involves η 6 interaction of the metal with the C 60 ligands and η 2-to-η 2 interactions between the C 60 ligands.

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.

Gas-Phase Reactions of Atomic Lanthanide Cations with Sulfur Hexafluoride: Periodicity in Reactivity

Room-temperature reactions of sulfur hexafluoride (SF6) have been surveyed systematically with atomic lanthanide cations (Ln+, excluding Pm+) in the gas phase, using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients and product distributions were measured in helium at a pressure of 0.35 Torr and temperature of 295 K. All the Ln+ cations were observed to react efficiently (k/kc > 0.24) and predominantly by single and multiple F atom and fluoride abstraction to produce both LnFn+ and SFn+(where n = 1, 2, 3). The observed periodic trend in reaction efficiency along the lanthanide row matches the periodic trend in the electron-promotion energy of the Ln+ cation. A remarkable Arrhenius-like correlation is observed for the dependence of reactivity on promotion energy: the early and late lanthanide cations exhibit effective temperatures of 45 500 and 14 000 K, respectively. SFn+ product ions are observed to be unreactive with SF6, whereas up to two molecules of SF6 have been observed to add to LnFn+ product ions under the experimental operating conditions of the ICP/SIFT tandem mass spectrometer.

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.

Carbon Disulfide Reactions with Atomic Transition-Metal and Main-Group Cations: Gas-Phase Room-Temperature Kinetics and Periodicities in Reactivity

The reactions of 46 atomic-metal cations with CS2 have been investigated at room temperature using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients and products were measured for the reactions of fourth-period atomic ions from K+ to Se+, of fifth-period atomic ions from Rb+ to Te+ (excluding Tc+), and of sixth-period atomic ions from Cs+ to Bi+. Primary reaction channels were observed leading to S-atom transfer, CS2 addition and, with Hg+, electron transfer. S-atom transfer appears to be thermodynamically controlled and occurs exclusively, and with unit efficiency, in the reactions with most early transition-metal cations (Sc+, Ti+, Y+, Zr+, Nb+, La+, Hf+, Ta+, and W+) and with several main-group cations (As+, Sb+) and less efficiently with Se+, Re+ and Os+. Other ions, including most late transition and main-group metal cations, react with CS2 with measurable rates mostly through CS2 addition or not at all (K+, Rb+, Cs+). Traces of excited states (< 10%) were seen from an inspection of the observed product ions to be involved in the reactions with Mo+, Te+, Ba+ and Au+ and possibly Pt+ and Ir+. The primary products YS+, ZrS+, NbS+, HfS+, TaS+, WS+, ReS+ and OsS+ react further by S-atom transfer to form MS2(+), and TaS2(+) reacts further to form TaS3(+). CS2 addition occurs with the cations MCS2(+), MS+, MS2(+), CS2(+), and TaS3(+) to form M+(CS2)(n) (n < or = 4), MS+(CS2)(n) (n < or = 4), MS2(+)(CS2)(n) (n < or = 3), (CS2)2(+) and TaS3(+)(CS2). Up to four CS2 molecules add sequentially to bare metal cations and monosulfide cations, and three to disulfide cations. Equilibrium constant measurements are reported that provide some insight into the standard free energy change for CS2 ligation. Periodic variations in deltaG degrees are as expected from the variation in electrostatic attraction, which follows the trend in atomic-ion size and the trend in repulsion between the orbitals of the atomic cations and the occupied orbitals of CS2.