Showing papers by "P. B. Armentrout published in 1992"
TL;DR: In this paper, a qualitative theoretical treatment of the singlet and triplet potential energy curves that arise when a single bond formed by an electron pair is cleaved either homolytically or H2-2H dissociation is presented.
Abstract: : When considering the fragmentation of a single bond, the attractive singlet and repulsive triplet potential energy curves of the prototype H2 - 2 H dissociation often come to mind. For species in which homolytic bond cleavage is energetically favored, such comparisons are reasonable. For other species where heterolytic cleavage gives lower-energy products, the H2 analogy is inappropriate. This paper offers a qualitative theoretical treatment of the singlet and triplet potential energy curves that arise when a single bond formed by an electron pair is cleaved either homolytically or heterolytically. This analysis is shown to provide insight into several problems involving transition metal systems: transition metal carbonyls, metal ion-ligand complexes, and transition metal dimers.
196 citations
TL;DR: In this paper, the kinetic energy dependence of the collision-induced dissociation (CID) of Ti+n (n=2−22) with Xe was studied by using a guided ion beam mass spectrometer.
Abstract: The kinetic energy dependence of the collision‐induced dissociation (CID) of Ti+n (n=2–22) with Xe is studied by using a guided ion beam mass spectrometer. Examination of the CID cross section behavior over a broad collision energy range demonstrates that Ti+n clusters dissociate exclusively by sequential loss of Ti atoms. Bond energies of ionic titanium clusters, D0(Ti+n−1–Ti), are determined from measurements of the CID thresholds. D0(Ti+n−1–Ti) are found to change significantly as a function of cluster size, with local maxima at n=7, 13, and 19. This pattern of highly stable cluster ions suggests that titanium cluster ions favor icosahedral structures.
166 citations
TL;DR: In this article, the authors measured the cross sections for collision-induced dissociation of SFx+ (x=1−5) with Xe using guided ion beam mass spectrometry.
Abstract: Guided ion beam mass spectrometry is used to measure the cross sections for collision‐induced dissociation of SFx+ (x=1–5) with Xe. The energy dependences of the cross sections are analyzed to give the following 0 K bond dissociation energies (BDEs): D°(SF4+–F)=4.60±0.10 eV, D°(SF3+–F)=0.36±0.05 eV, D°(SF2+–F)=4.54±0.08 eV, D°(SF+–F)=4.17±0.10 eV, and D°(S+–F)=3.56±0.05 eV. The ionization energies, IE(SF)=10.16±0.17 eV, IE(SF3)=8.18±0.07 eV, IE(SF4)=11.69±0.06 eV, and IE(SF5)=9.60±0.05 eV, are also measured from analysis of endothermic charge–transfer reactions. From these BDEs and IEs, we derive heats of formation for the sulfur fluoride ions and neutrals that provide a self‐consistent set of thermochemical data for the sulfur fluoride species. In some cases, the thermochemical values determined here are considerably different from available literature values. These differences are discussed in detail.
107 citations
TL;DR: In this article, the kinetic energy dependence of the collision-induced dissociation (CID) of Ni+n (n=2−18) with xenon was studied by using a guided ion beam mass spectrometer.
Abstract: The kinetic energy dependence of the collision‐induced dissociation (CID) of Ni+n (n=2–18) with xenon is studied by using a guided ion beam mass spectrometer. Bond energies of nickel cluster ions, D0(Ni+n−1–Ni), are determined from measurements of the CID thresholds. Bond energies for neutral nickel clusters, D0(Nin−1–Ni), are derived by combining these ionic bond energies with literature values of ionization energies for Nin. Both D0(Ni+n−1–Ni) and D0(Nin−1–Ni) are found to increase nonmonotonically as a function of cluster size, with local maxima at n=3, 7, and 13 for ionic clusters and at n=6 and 13 for neutral clusters. Examination of the cluster size dependence of nickel cluster bond energies leads to speculations on the likely cluster geometric structures. Examination of the general dissociation behavior over a broad collision energy range shows that nickel cluster ions dissociate primarily by sequential atom loss, although exceptions are noted.
90 citations
79 citations
TL;DR: In this article, the authors studied the reaction of N+4 ions with H2, HD, and D2 under single-collision conditions in a guided ion beam mass spectrometer.
Abstract: Reactions of N+4 ions with H2, HD, and D2 are studied from thermal to 5 eV kinetic energy under single‐collision conditions in a guided‐ion beam mass spectrometer. Reactant ions are formed in a flow tube source to ensure thermalization. Despite being exothermic by 1.5 eV, formation of N2H+ (N2D+) is observed to proceed with an activation barrier that we measure to be 0.09±0.03 eV at 0 K, independent of the hydrogen isotopomer used. Possible reaction mechanisms are discussed, and the present results are compared to previous flow and drift tube measurements. Effects of collisional reheating on the derivation of thermochemistry in drift‐tube experiments are discussed. We also discuss the difficulty of deriving reliable thermochemistry from pseudo‐Arrhenius plots when the mathematical form of the cross section excitation function is unknown.
60 citations
TL;DR: In this article, the authors measured the cross sections of gas-phase endothermic reactions between MO+ (M=Sc, Y, and La) and NO_2 in a guided ion beam mass spectrometer.
57 citations
TL;DR: In this article, threshold collisional activation of FeC 2 H 6 + was studied in a guided-ion beam mass spectrometer, where parent ions are formed by reaction of Fe + with either ethane or acetone in a flow tube ion source which ensures their thermalization.
Abstract: Threshold collisional activation (TCA) of FeC 2 H 6 + is studied in a guided-ion beam mass spectrometer. Parent ions are formed by reaction of Fe + with either ethane or acetone in a flow tube ion source which ensures their thermalization. We present evidence that ions formed in the two ways have different structures corresponding to Fe + -ethane and Fe + -dimethyl, respectively
45 citations
TL;DR: In this article, the authors measured cross sections as a function of reagent collision energy for the reaction of Al + ( 1 S) with NO 2, N 2 O, and CO 2 by using guided-ion-beam mass spectrometry.
Abstract: Cross sections as a function of reagent collision energy are measured for the reaction of Al + ( 1 S) with NO 2 , N 2 O, and CO 2 by using guided-ion-beam mass spectrometry. In the NO 2 system, NO + +AlO and AlO + +NO are formed in endothermic reactions. The threshold for the former reaction is used to measure the bond energy, D o 0 (AlO)=123.1±1.0 kcal/mol, in good agreement with the presently accepted value of 121.2±2.2 kcal/mol.
39 citations
TL;DR: In this article, the authors studied the reactions of protonated water dusters with deuterated ammonia by using guided ion beam mass spectrometry and determined the reaction cross-sections as a function of collision energy from thermal energy to over 10eV.
35 citations
TL;DR: Guided ion beam mass spectrometry was used to study the reactions of ground-state Cr{sup +}({sup 6}S) with propane, butane, methylpropane, dimethylpropane and selectivity deuteriated propane and methylpropANE as discussed by the authors.
Abstract: Guided ion beam mass spectrometry is used to study the reactions of ground-state Cr{sup +}({sup 6}S) with propane, butane, methylpropane, dimethylpropane, and selectivity deuteriated propane and methylpropane. Thermal energy reactions of Cr{sup +}({sup 6}S) with 4-octyne are also investigated. Ground-state Cr{sup +} ions undergo no bimolecular reactions at thermal energies with any of the alkanes, but do react at elevated kinetic energies. The only products formed at thermal energy in the alkane systems are the collisionally stabilized adduct complexes. Approximate lifetimes for these adducts are determined. Analyses of the endothermic processes in the alkane systems yields 298 K bond energies for several chromium-ligand species. These include the neutral and ionic chromium methyl species [D{degrees}(Cr-CH{sub 3}) = 37.9 {+-} 2.0 kcal/mol and D{degrees}(Cr{sup +}-CH{sub 3}) = 30.3 {+-} 1.7 kcal/mol], several other chromium ion-alkyl species [D{degrees}(Cr{sup +}-C{sub 2}H{sub 5}) = 35.0 {+-} 2.1 kcal/mol, D{degrees}(Cr{sup +}-1-C{sub 3}H{sub 7}) = 32.1 {+-} 1.4 kcal/mol, D{degrees} (Cr{sup +}-2-C{sub 3}H{sub 7}) = 28.5 {+-} 1.3 kcal/mol], and chromium ion-vinyl and -various alkylidenes [D{degrees}(Cr{sup +}-C{sub 2}H{sub 3}) = 59.0 {+-} 2.3 kcal/mol, D{degrees}[Cr{sup +}=CHCH{sub 3}] = 52 {+-} 3 kcal/mol, D{degrees}[Cr{sup +}=CHCH{sub 2}CH{sub 3}] = 36 {+-} 3 kcal/mol, D{degrees}[Cr{sup +}=C(CH{sub 3}){sub 2}] = 39more » {+-} 3 kcal/mol]. The observed reactivity requires unusual reaction mechanisms that are discussed in detail. 60 refs., 9 figs., 4 tabs.« less
TL;DR: In this article, the reaction proceeds at the rate predicted by the classical ion-molecule capture collision theory at thermal energy, but exceeds this prediction at energies above 1 eV.
Abstract: Reactions of N+2 ions with H2, HD, and D2 are studied under single‐collision conditions in a guided‐ion beam mass spectrometer over a much broader range of interaction energies than in any previous study, including the low energy region of thermal to 01 eV Reactant ions are formed in a flow tube source to ensure thermalization Possible reaction mechanism are discussed, and the present results are compared to previous measurements We find that the reaction proceeds at the rate predicted by the classical ion–molecule capture collision theory at thermal energy, but exceeds this prediction at energies above 01 eV This behavior is discussed and attributed to details of the interaction between the N+2+H2 surface and the N2+H+2 surface along which the hydrogen atom transfer reaction proceeds Intramolecular isotope effects and product ion dissociation behavior suggest that the reaction occurs via a direct mechanism with no long‐lived intermediate at elevated energies
TL;DR: In this article, the effect of electronic energy as well as kinetic energy on the reactivity of atomic chromium ions is examined and reveals several interesting aspects of Cr{sup +} chemistry.
Abstract: Guided ion beam mass spectrometry is used to study the reactions of excited states of Cr{sup +} with propane, butane, methylpropane, and dimethylpropane. The effect of electronic energy as well as kinetic energy on the reactivity of atomic chromium ions is examined and reveals several interesting aspects of Cr{sup +} chemistry. The present results include the first direct evidence for reaction of the Cr{sup +}({sup 6}D) first excited state. Most interesting is the observation that the excited quartet states of Cr{sup +} react with alkanes very differently than ground-state Cr{sup +}({sup 6}S) activates only C-C bonds of alkanes, while in the present study we find that the excited Cr{sup +}({sup 6}S). Previously we found that Cr{sup +}({sup 6}S) activates only C-C bonds of alkanes, while in the present study we find that the excited Cr{sup +}({sup 4}d, {sup 4}g) states activates both C-H and C-C bonds of alkanes. The reactivity of the {sup 6}D first excited state of Cr{sup +} is similar to that of the {sup 6}S ground state. These reaction systems are currently the only examples where electronic excitation of a transition-metal ion drastically changes the products formed. 32 refs., 4 figs., 5 tabs.
TL;DR: In this paper, the adiabatic ionization energy (IE) of NO2 was measured to be 9.60±0.03 eV by studying the charge transfer reactions of Zn+, NO+, and CH3I+ with NO2 and those of NO+2 with α,α,α-trifluorotoluene and CH 3I using guided ion-beam mass spectrometry.
Abstract: The adiabatic ionization energy (IE) of NO2 is measured to be 9.60±0.03 eV by studying the charge‐transfer reactions of Zn+, NO+, and CH3I+ with NO2 and those of NO+2 with α,α,α‐trifluorotoluene and CH3I using guided ion‐beam mass spectrometry. This value confirms the accuracy of a very precise spectroscopic value measured by Haber et al. [J. Chem. Phys. 144, 58 (1988)] and Tanaka and Jursa [J. Chem. Phys. 36, 2493 (1962)], IE(NO2)=9.586±0.002 eV, but is much lower than many other measurements that are limited by very unfavorable Franck–Condon factors. The mechanism that allows the charge‐transfer reactions to occur at the thermodynamic limit is discussed by examining qualitative potential‐energy surfaces for the charge‐transfer processes.
TL;DR: In this paper, the reaction of ground-state Si + (2 P) with methylsilane (SiH 3 CH 3 ) was studied from thermal to 10-eV kinefic energy by using guided ion beam mass spectrometry.
Abstract: Reaction of ground-state Si + ( 2 P) with methylsilane (SiH 3 CH 3 ) is studied from thermal to 10-eV kinefic energy by using guided ion beam mass spectrometry. The major products at thermal energies are SiCH 3 + , Si 2 HCH 3 + , and, above 1 eV, SiH 2 CH 3 + . Labeling experiments involving 30 Si + provide additional mechanistic information that SiCH 3 + formed via three different mechanisms
01 Jan 1992
TL;DR: The concept of intrinsic metal-ligand bond energy is defined and used to consider the strengths of bonds in coordinatively saturated metal-linear compounds in this paper, and studies of the thermochemistry of proposed reactive intermediates for the reactions of Fe+ and Co+ with small alkanes are discussed with an emphasis on understanding the potential energy surfaces for C-H and C-C bond activation processes.
Abstract: Dissociation energies for a variety of bonds between transition metals and simple ligands comprised of hydrogen, carbon, nitrogen, and oxygen have been measured by using the technique of guided ion beam mass spectrometry. For species that form covalent bonds with the metals, the bond energies are found to correlate with the energy necessary to promote the bare metal atom or ion into an electron configuration suitable for bonding. The trends in the bond energies of M+ to isoelectronic series of ligands, CH3, NH2 and OH or CH2, NH and 0, are used to quantify the contributions of covalent and dative bonding for these ligands. The strength of the dative interactions is found to depend on the number of electron lone-pairs on the ligands and the number of empty or half-filled d orbitals on the metal. The concept of an intrinsic metal-ligand bond energy is defined and used to consider the strengths of bonds in coordinatively saturated metal-ligand compounds. Initial studies that address the metal-ligand bond energies in such species more directly include measurements of the sequential bond energies of M(CO)X + (x = 1–6), M(H20)x + (x = 1–4) and M(CH4)X + (x = 1–4). Variations in these bond energies as the number of ligands increases are interpreted by considering how the valence electrons on the metal reorganize to accommodate the ligand shell. Finally, studies of the thermochemistry of proposed reactive intermediates for the reactions of Fe+ and Co+ with small alkanes are discussed with an emphasis on understanding the potential energy surfaces for C-H and C-C bond activation processes.
TL;DR: In this paper, the reaction of CO + 2 with 0 2 over a range of kinetic energies with a guided ion beam apparatus and with a variable-temperature selected-ion flow drift tube was investigated.
08 Sep 1992
TL;DR: In this paper, the MPD-REMPI and time-of-flight photoelectron spectra (TOF•PES) of Fe(C5H5)2, Co(C 5H5), and Ni(Ni) were obtained in the range 380-390 nm and 445-455 nm, respectively.
Abstract: Laser multiphoton dissociation–resonance‐enhanced multiphoton ionization (MPD–REMPI) and time‐of‐flight photoelectron spectra (TOF‐PES) of Fe(C5H5)2, Co(C5H5)2, and Ni(C5H5)2 have been obtained in the range 380–390 nm, and the MPD–REMPI of Fe(C5H5)2 and Co(C5H5)2 have been obtained in the range 445–455 nm. The only ions produced by the pulsed dye laser are Fe+, Co+, and Ni+. Transitions observed in the MPD–REMPI spectra are assigned to resonant states of the neutral atoms. Final states of the atomic ions are determined from the TOF‐PES spectra. For Ni and Co, there appears to be a propensity for core preservation of the resonant state upon ionization if the resonant state has an electron configuration with an electron in a d‐type Rydberg orbital. For Fe, no such propensity is observed.
TL;DR: In this paper, the cross sections as a function of kinetic energy were measured for reaction of SiH4 with O+, O2+, and N2+ with O4S, O2+ (2Πg,v=0), N2+(2Σg+,v = 0).
Abstract: Guided ion beam mass spectrometry is used to measure the cross sections as a function of kinetic energy for reaction of SiH4 with O+(4S), O2+ (2Πg,v=0), N+(3P), and N2+(2Σg+,v=0). All four ions react with silane by dissociative charge-transfer to form SiHm+ (m=0−3), and all but N2+ also form SiXHm+ products where (m=0−3) andX=O, O2 or N. The overall reactivity of the O+, O2+, and N+ systems show little dependence on kinetic energy, but for the case of N2+, the reaction probability and product distribution relies heavily on the kinetic energy of the system. The present results are compared with those previously reported for reactions of the rare gas ions with silane [13] and are discussed in terms of vertical ionization from the 1t2 and 3a1 bands of SiH4. Thermal reaction rates are also provided and dicussed.
01 Jan 1992
TL;DR: In this paper, the reactions of both main group and transition metal atomic ions with H 2, D 2, and HD have been studied as a function of kinetic energy by using guided ion beam mass spectrometry.
Abstract: Reactions of both main group and transition metal atomic ions with H 2 , D 2 , and HD have been studied as a function of kinetic energy by using guided ion beam mass spectrometry For most ions, the observed behavior falls into several distinct groups (statistical, direct and impulsive) that can be used to characterize the potential energy surfaces for the reactions These categories facilitate the comparison of the reactivity of the main group metals to that for the transition metals
TL;DR: Guided ion beam mass spectrometry was used to study the reactions of ground-state Cr{sup +}({sup 6}S) with propane, butane, methylpropane, dimethylpropane and selectivity deuteriated propane and methylpropANE as discussed by the authors.
Abstract: Guided ion beam mass spectrometry is used to study the reactions of ground-state Cr{sup +}({sup 6}S) with propane, butane, methylpropane, dimethylpropane, and selectivity deuteriated propane and methylpropane. Thermal energy reactions of Cr{sup +}({sup 6}S) with 4-octyne are also investigated. Ground-state Cr{sup +} ions undergo no bimolecular reactions at thermal energies with any of the alkanes, but do react at elevated kinetic energies. The only products formed at thermal energy in the alkane systems are the collisionally stabilized adduct complexes. Approximate lifetimes for these adducts are determined. Analyses of the endothermic processes in the alkane systems yields 298 K bond energies for several chromium-ligand species. These include the neutral and ionic chromium methyl species [D{degrees}(Cr-CH{sub 3}) = 37.9 {+-} 2.0 kcal/mol and D{degrees}(Cr{sup +}-CH{sub 3}) = 30.3 {+-} 1.7 kcal/mol], several other chromium ion-alkyl species [D{degrees}(Cr{sup +}-C{sub 2}H{sub 5}) = 35.0 {+-} 2.1 kcal/mol, D{degrees}(Cr{sup +}-1-C{sub 3}H{sub 7}) = 32.1 {+-} 1.4 kcal/mol, D{degrees} (Cr{sup +}-2-C{sub 3}H{sub 7}) = 28.5 {+-} 1.3 kcal/mol], and chromium ion-vinyl and -various alkylidenes [D{degrees}(Cr{sup +}-C{sub 2}H{sub 3}) = 59.0 {+-} 2.3 kcal/mol, D{degrees}[Cr{sup +}=CHCH{sub 3}] = 52 {+-} 3 kcal/mol, D{degrees}[Cr{sup +}=CHCH{sub 2}CH{sub 3}] = 36 {+-} 3 kcal/mol, D{degrees}[Cr{sup +}=C(CH{sub 3}){sub 2}] = 39more » {+-} 3 kcal/mol]. The observed reactivity requires unusual reaction mechanisms that are discussed in detail. 60 refs., 9 figs., 4 tabs.« less
TL;DR: In this paper, the laser multiphoton dissociation (MPD) spectra of VOCl 3 have been obtained in the ranges 430-440 and 380-390 nm, and both the V + and VO + spectra are continuous and structureless.