Showing papers by "P. B. Armentrout published in 2020"
TL;DR: The ThO 2+ bond energy is larger than those of its transition metal congeners, TiO2+ and ZrO2+, which can be attributed partially to an actinide contraction, but also to contributions from the participation of f orbitals on thorium that are unavailable to the transition metal systems.
Abstract: Kinetic energy dependent reactions of ThO+ with O2 are studied using a guided ion beam tandem mass spectrometer. The formation of ThO2+ in the reaction of ThO+ with O2 is observed to be slightly endothermic and also exhibits two obvious features in the cross section. These kinetic energy dependent cross sections were modeled to determine a 0 K bond dissociation energy of D0(OTh+-O) = 4.94 ± 0.06 eV. This value is slightly larger but within experimental uncertainty of less precise previously reported experimental values. The higher energy feature in the ThO2+ cross section was also analyzed and suggests formation of an excited state of the product ion lying 3.1 ± 0.2 eV above the ground state. Additionally, the thermochemistry of ThO2+ was explored by quantum chemical calculations, including a full Feller-Peterson-Dixon (FPD) composite approach with correlation contributions up to CCSDT(Q) and four-component spin-orbit corrections, as well as more approximate CCSD(T) calculations including semiempirical estimates of spin-orbit energy contributions. The FPD approach predicts D0(OTh+-O) = 4.87 ± 0.04 eV, in good agreement with the experimental value. Analogous FPD results for ThO+, ThO, and ThO2 are also presented, including ionization energies for both ThO and ThO2. The ThO2+ bond energy is larger than those of its transition metal congeners, TiO2+ and ZrO2+, which can be attributed partially to an actinide contraction, but also to contributions from the participation of f orbitals on thorium that are unavailable to the transition metal systems.
17 citations
TL;DR: Evaluation of the uncertainty in the derivation from association kinetics measurements, including uncertainties in collisional energy transfer, calculated harmonic frequencies, and possible contribution of isomerization of the association complexes indicates than an uncertainty of ±0.2 eV should be expected, and an Uncertainty of better than±0.1 eV is unlikely to be reasonable.
Abstract: The bond dissociation energies at 0 K (BDE) of Au2+-CH4 and Au2CH4+-CH4 have been determined using two separate experimental methods. Analyses of collision-induced dissociation cross sections for Au2CH4+ + Xe and Au2(CH4)2+ + Xe measured using a guided ion beam tandem mass spectrometer (GIBMS) yield BDEs of 0.71 ± 0.05 and 0.57 ± 0.07 eV, respectively. Statistical modeling of association kinetics of Au2(CH4)0-2+ + CH4 + He measured from 200 to 400 K and at 0.3-0.9 Torr using a selected-ion flow tube (SIFT) apparatus yields slightly higher values of 0.81 ± 0.21 and 0.75 ± 0.25 eV. The SIFT data also place a lower limit on the BDE of Au2C2H8+-CH4 of 0.35 eV, likely an activated isomer, not Au2(CH4)2+-CH4. Particular emphasis is placed on determining the uncertainty in the derivation from association kinetics measurements, including uncertainties in collisional energy transfer, calculated harmonic frequencies, and possible contribution of isomerization of the association complexes. This evaluation indicates that an uncertainty of ±0.2 eV should be expected and that an uncertainty of better than ±0.1 eV is unlikely to be reasonable.
10 citations
TL;DR: Threshold collision-induced dissociation of Th(OH)3+(H2O)n (n = 1 - 4) with xenon was performed using a guided ion beam tandem mass spectrometer (GIBMS) and values agree reasonably well with values calculated at the B3LYP, B3PW91, and PBE0 levels of theory with cc-pVQZ basis sets.
Abstract: Threshold collision-induced dissociation of Th(OH)3+(H2O)n (n = 1-4) with xenon was performed using a guided ion beam tandem mass spectrometer. The primary dissociation pathway for all complexes is a loss of a single water molecule followed by the sequential loss of additional water molecules at higher collision energies. The data were analyzed using a statistical model after accounting for lifetime effects and reactant internal and kinetic energy distributions to obtain 0 K bond dissociation energies (BDEs). These were also converted using rigid rotor/harmonic oscillator approximations to yield thermodynamic values at room temperature. The 0 K BDEs of H2O ligands to Th(OH)3+ (IV) are experimentally determined for the first time as 106 ± 6, 89 ± 6, 76 ± 4, and 51 ± 4 kJ/mol for the first, second, third, and fourth water ligand added. These values agree reasonably well with values calculated at the B3LYP, B3PW91, and PBE0 levels of theory with aug-cc-pVQZ basis sets, whereas B3LYP-GD3BJ, MP2, and CCSD(T) single point energies with (without) counterpoise corrections systematically overestimate the bond energies by about 15 (20), 19 (25), and (18) kJ/mol, respectively.
7 citations
TL;DR: Results are consistent with the hypothesis that the distinction of in-plane and out-of-plane CS symmetry in the triatomic systems might be the explanation for the two endothermic features observed in the Re+ + O2 reaction.
Abstract: The kinetic energy dependent reactions of Re+ with SO2 were studied with guided ion beam tandem mass spectrometry. ReO+, ReO2+, and OReS+ species were observed as products, all in endothermic reactions. Modeling of the kinetic energy dependent cross sections yields 0 K bond dissociation energies (BDEs, in eV) of 4.78 ± 0.06 (Re+-O), 5.75 ± 0.02 (Re+-O2), and 4.35 ± 0.14 (Re+-SO). The latter two values can be combined with other information to derive the additional values 6.05 ± 0.05 (ORe+-O) and 4.89 ± 0.19 (ORe+-S). BDEs of ReO+ and ReO2+ agree with literature values whereas the values for OReS+ are the first measurements. The former result is obtained even though formation of ground state ReO+ is spin-forbidden. Quantum mechanical calculations at the B3LYP level of theory with a def2-TZVPPD basis set yield results that agree reasonably well with experimental values. Additional calculations at the BP86 and CCSD(T) levels of theory using def2-QZVPPD and aug-cc-pVxZ (x = T, Q, and 5) basis sets were performed to compare thermochemistry with experiment to determine that ReO2+ rather than the isobaric ReS+ is formed. Product ground states are 3Δ3(ReO+), 3B1(OReO+), 5Π-1(ReS+), and 3A''(OReS+) after including empirical spin-orbit corrections, which means that formation of ground state products is spin-forbidden for all three product channels. The potential energy surfaces for the ReSO2+ system were also explored at the B3LYP/def2-TZVPPD level and exhibited no barriers in excess of the endothermicities for all products. BDEs for rhenium oxide and sulfide diatomics and triatomics are compared and discussed. The present result for formation of ReO+ is compared to that for formation of ReO+ in the reactions of Re+ + O2 and CO, where the former system exhibited interesting dual cross section features. Results are consistent with the hypothesis that the distinction of in-plane and out-of-plane CS symmetry in the triatomic systems might be the explanation for the two endothermic features observed in the Re+ + O2 reaction.
6 citations
TL;DR: The kinetic-energy dependence of SO2 activated by Os+ was studied by guided ion beam tandem mass spectrometry and the PESs show that none of the reactions have barriers in excess of the product endothermicities.
Abstract: The kinetic-energy dependence of SO2 activated by Os+ was studied by guided ion beam tandem mass spectrometry. Species observed in endothermic reactions were OsO+, OsO2+ or OsS+, and OOsS+. The kin...
5 citations
TL;DR: Infrared action spectra of the product ions along with quantum-chemical calculations unambiguously show that dehydration consistently produces fragment ions containing an oxazoline moiety, contrast with the common oxazolone structure that would result from dehydration at the C-terminus analogous to the common b/y dissociation forming regular b2-type sequence ions.
5 citations
TL;DR: Spectral comparison for both metallated species indicates that the relative stability of the dominant zwitterionic species appears to be described more accurately than the MP2(full) level.
Abstract: Metallated gas-phase structures consisting of a deprotonated and an intact histidine (His) ligand, yielding M(His-H)(His)+, where M = Zn and Cd, were examined with infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light from a free-electron laser (FEL). In parallel, quantum chemical calculations identified several low-energy isomers for each complex. Experimental action spectra were compared to linear spectra calculated at the B3LYP level of theory using the 6-311+G(d,p) and def2-TZVP basis sets for the zinc and cadmium complexes, respectively. For both Zn and Cd species, the definitive assignment is complicated by conflicting relative energetics, which were calculated at B3LYP, B3LYP-GD3BJ, B3P86, and MP2(full) levels. Spectral comparison for both species indicates that the dominant conformation, [Nα,Nπ,CO-][CO2-](NπH+), has the deprotonated His chelating the metal at the amine nitrogen, π nitrogen of the imidazole ring, and the deprotonated carbonyl oxygen and that the intact His ligand adopts a salt-bridge bidentate binding motif, coordinating the metal with both carboxylate oxygens. There is also evidence for a conformation where the deprotonated His coordination is maintained, but the intact His ligand adopts a more canonical structure, coordinating with the metal atom at the amine nitrogen and π nitrogen, [Nα,Nπ,CO-][Nα,Nπ]gtgg. For both metallated species, B3LYP, B3P86, and B3LYP-GD3BJ levels of theory appear to describe the relative stability of the dominant zwitterionic species more accurately than the MP2(full) level.
5 citations
TL;DR: In this paper, the effects of multiple collisions, dissociation lifetimes, reactant internal and kinetic energy distributions, competition among channels, and evolution into sequential channels were examined for decomposition of the protonated tripeptide, GlyProAla (H+GPA), through collision-induced dissociation with Xe in a guided ion beam tandem mass spectrometer.
4 citations
TL;DR: Comparing the D2 data to that obtained previously in earlier experiments but unpublished shows that the earlier data, which utilized a surface ionization source of V+, and the state-selected data for V+(a5D2) are essentially identical in the threshold regions where they overlap, and this conclusion is validated by high-level ab initio calculations.
Abstract: Recent electronic state-selected measurements of the reactions of atomic vanadium cations with D2 and CO2 are reanalyzed to properly account for the kinetic energy distribution of the reactant neut...
4 citations