Showing papers by "Lester Andrews published in 2003"
TL;DR: The structure and properties of the monocarbides ScC, TiC, VC, CrC, MnC, FeC, CoC, NiC, CuC, ZnC and their negatively and positively charged ions together with 3d-metal monoxide cations are calculated by density functional theory (DFT) and hybrid DFT methods as mentioned in this paper.
Abstract: The structure and properties of the monocarbides ScC, TiC, VC, CrC, MnC, FeC, CoC, NiC, CuC, ZnC and their negatively and positively charged ions together with 3d-metal monoxide cations are calculated by density functional theory (DFT) and hybrid DFT methods. In addition to the spectroscopic constants, the computed properties include the electron affinities, ionization energies, and dissociation energies. These results along with our previous results for the neutral and negatively charged 3d-metal monoxides allow a detailed comparison of similarity and differences in the bonding of the metal oxides and carbides. These results are compared with results obtained using other theoretical approaches and with experiment. Chemical bonding, analyzed using the natural bond orbital scheme, was found to be rather different in the 3d-metal monocarbides and monoxides.
150 citations
TL;DR: This work provides the first evidence for noble gas-actinide complexes, and the first example of neutral complexes with four noble gas atoms bonded to one metal center, as well as four distinct CUO(Ar)(4-n)(Ng)(n) complexes.
Abstract: Laser-ablated U atoms react with CO in excess argon to produce CUO, which is trapped in a triplet state in solid argon at 7 K, based on agreement between observed and relativistic density functional theory (DFT) calculated isotopic frequencies (12C16O, 13C16O, 12C18O). This observation contrasts a recent neon matrix investigation, which trapped CUO in a linear singlet state calculated to be about 1 kcal/mol lower in energy. Experiments with krypton and xenon give results analogous to those with argon. Similar work with dilute Kr and Xe in argon finds small frequency shifts in new four-band progressions for CUO in the same triplet states trapped in solid argon and provides evidence for four distinct CUO(Ar)4-n(Ng)n (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes for each Ng. DFT calculations show that successively higher Ng complexes are responsible for the observed frequency progressions. This work provides the first evidence for noble gas−actinide complexes, and the first example of neutral complexes with four n...
120 citations
TL;DR: In this article, the authors identified new molecular anions from matrix infrared spectra with isotopic substitution (HD, D(2), and H(2) + D (2)) and comparison to frequencies calculated by density functional theory.
Abstract: Gold is noble, but excited gold is reactive. Reactions of laser-ablated copper, silver, and gold with H(2) in excess argon, neon, and pure hydrogen during condensation at 3.5 K give the MH molecules and the (H(2))MH complexes as major products and the MH(2)(-) and AuH(4)(-) anions as minor products. These new molecular anions are identified from matrix infrared spectra with isotopic substitution (HD, D(2), and H(2) + D(2)) and comparison to frequencies calculated by density functional theory. The stable linear MH(2)(-) anions are unique in that their corresponding neutral MH(2) molecules are higher in energy than M + H(2) and thus unstable to M + H(2) decomposition. Infrared spectra are observed for the bending modes of AuH(2), AuHD, and AuD(2) in solid H(2), HD, and D(2), respectively. The observation of square-planar AuH(4)(-) attests the stability of the higher Au(III) oxidation state for gold. The synthesis of CuH(2)(-) in solid compounds has potential for use in hydrogen storage.
83 citations
TL;DR: In this paper, a matrix-isolation infrared spectroscopy of chromium atoms with molecular hydrogen is investigated through a comparison with DFT (density functional theory) and MP2 calculations of vibrational fundamentals.
Abstract: Reactions of chromium atoms with molecular hydrogen are investigated through matrix-isolation infrared spectroscopy of products and complexes. Laser-ablated chromium atoms react with molecular hydrogen upon condensation in excess neon and argon and in pure hydrogen. The reaction products, CrH, (H2)CrH, CrH2, (H2)CrH2, and (H2)2CrH2 are identified by isotopic substitution (D2, HD, and H2+D2) and comparison with DFT (density functional theory) and MP2 calculations of vibrational fundamentals. The (H2)CrH complex with lower energy than CrH3 is trapped and no band is observed for CrH3. Reactions with H2 and D2 mixtures and with HD give different relative yields of the same mixed isotopic bands, which shows that exchange of dihydride and dihydrogen complex positions occurs in the energized [CrH4]* intermediate in the formation of (H2)CrH2. The major bands at 1529.5 cm-1 for H2 and 1112.2 cm-1 for D2 in neon and at 1521.3 cm-1 in pure hydrogen and 1106.9 cm-1 in pure deuterium are due to (H2)2CrH2 and (D2)2CrD2...
70 citations
TL;DR: In this paper, laser-ablated coinage metal atom reactions with H2 in excess argon, neon, and pure hydrogen are investigated through matrix infrared spectroscopy, and the reaction products are identified by isotopic substitution (D2, HD, and H2 + D2) and verified by DFT calculations of vibrational fundamentals.
Abstract: Laser-ablated coinage metal atom reactions with H2 in excess argon, neon, and pure hydrogen are investigated through matrix infrared spectroscopy. The reaction products are identified by isotopic substitution (D2, HD, and H2 + D2) and verified by DFT calculations of vibrational fundamentals. The MH and (H2)MH molecules are observed for all group 11 metals, and the trihydride complex (H2)AuH3 is stabilized in pure hydrogen. The (H2)CuH and (H2)AgH complexes exhibit weak H−H stretching fundamentals at 3805.9 and 3566.6 cm-1 and strong Cu−H and Ag−H stretching modes at 1861.4 and 1742.6 cm-1, respectively. In addition, (H2)CuH reacts further with Cu to give (H2)CuHCu, and Au (2P) inserts to form AuH2 in pure hydrogen. The cluster hydrides M2H and M2H- anions are also formed in these experiments.
50 citations
TL;DR: In this article, the reaction of laser-ablated Ga atoms and normal hydrogen during co-deposition at 3.5 K gave GaH as the major product and GaH2, GaH3, GaG4, Ga2H5, and GaG6 as minor products.
Abstract: Reactions of laser-ablated Ga atoms and normal hydrogen during co-deposition at 3.5 K give GaH as the major product and GaH2, GaH3, GaH2-, GaH4-, and Ga2H2 as minor products. Identifications are based on infrared spectra, isotopic substitution (D2, H2 + D2 mixtures, HD), comparisons to earlier work, and frequencies calculated by density functional theory. Mercury arc radiation destroyed the GaH2- and GaH4- anions, decreased GaH and increased GaH3, destroyed Ga2H2, and produced new bands due to Ga2H4, two Ga2H5 radical isomers, and Ga2H6. ArF laser irradiation at 193 nm was particularly effective in converting GaH to GaH3 and to Ga2H6. The GaH4- anion absorptions in solid hydrogen are compatible with solid NaGaH4 bands: Near-ultraviolet excitation of GaD2- with D2 present increases GaD4- absorptions. Warming these samples to remove the H2 matrix replaced sharp gallium hydride molecular absorptions with broad 1800−2000, 1300−1700, and 600−700 cm-1 bands due to higher oligomers containing terminal and bridg...
49 citations
TL;DR: In this article, the electronic and geometrical structure of FenCO, FenCO−, and FenCO+ (n=2-6) were computed using density functional theory (DFT), and several hybrid and pure DFT methods were tested on FeCO and Fe2CO where experimental data were available.
Abstract: The electronic and geometrical structure of the ground and excited states of FenCO, FenCO−, and FenCO+ (n=2–6) are computed using density functional theory (DFT). Several hybrid and pure DFT methods are tested on FeCO and Fe2CO where experimental data are available. The pure DFT methods are superior to hybrid methods in reproduction of experimental spectroscopic data, except for the dissociation energy of FeCO. CO is twofold coordinated in Fe2CO, Fe3CO, and Fe4CO, threefold coordinated in Fe5CO, and fourfold in Fe6CO. While the Boudouard-type disproportionation reaction FenCO+CO→FenC+CO2 is endothermic by 1.59, 1.10, and 0.55 eV for FeCO, Fe2CO, and Fe3CO, respectively, it becomes exothermic beginning with n=4. The reaction barrier decreases from 3.5 eV for FeCO to 1.3 eV for Fe4CO. The most exothermic (by 0.42 eV) reaction is Fe6CO++CO→Fe6C++CO2. It is found that the catalytic ability increases with clusters size due to the decreasing FenC–O (or increasing Fen–C) bond strength. The Fen–CO binding energy ...
45 citations
TL;DR: In this paper, the Pd-C2H2 π complex is characterized by a C−C and C−H stretching mode near 1710 cm-1 and a 39.8 kcal/mol binding energy predicted by DFT.
Abstract: Laser-ablated palladium atoms react with acetylene in excess argon to form the strong Pd-η2-(C2H2) and Pd-η2-(C2H2)2 π complexes. The C−C and C−H stretching modes and two C−H deformation modes are observed in the matrix infrared spectrum and identified through isotopic substitution (13C2H2, C2D2, C2HD) and density functional theory (DFT) isotopic frequency calculations. The Pd(C2H2) complex is characterized by a C−C stretching mode near 1710 cm-1 and a 39.8 kcal/mol binding energy predicted by DFT. The antisymmetric C−C stretching mode for Pd-η2-(C2H2)2 is observed at 1765 cm-1. The Pd2-η2-(C2H2) complex produced from the reaction of two Pd atoms with C2H2 is characterized by a C−C mode at 1566 cm-1. The interaction between atomic Pd and C2H2 involves a small amount of charge transfer based on NBO analysis, which is enhanced by a Pd2 dimer coordinated to C2H2. As a result, Pd2 dimer can reduce the C−C triple bond to a double bond. These complexes represent first steps in the Pd−C2H2 interaction culminatin...
37 citations
TL;DR: In this article, laser-ablated Cr atoms react with CO (12C16O, 13C 16O, 12C18O) in excess argon to give the same Cr(CO)3,4,5 species observed from the photodissociation of Cr6.
Abstract: Laser-ablated Cr atoms react with CO (12C16O, 13C16O, 12C18O) in excess argon to give the same Cr(CO)3,4,5 species observed from the photodissociation of Cr(CO)6. Similar reactions in excess neon give neon matrix fundamentals between argon matrix and gas-phase values. The dicarbonyl Cr(CO)2 is bent with 1970.8, 1821.5 cm-1 and 1982.1, 1832.9 cm-1 C−O stretching fundamentals in solid argon and neon, respectively. The high-spin CrCO molecule appears at 1975.6 and 2018.4 cm-1 in solid argon and neon, respectively, and exhibits a strong matrix interaction. The CrCO+ cation and Cr(CO)2- anion are observed in laser-ablation experiments in solid neon at 2200.7 and 1705.0 cm-1, respectively. The Cr2(CO)2 complex absorbs strongly at 1735.4 cm-1 and gives several combination bands in neon. Density functional theory calculations support the vibrational assignments.
28 citations
01 May 2003
TL;DR: In this article, the electronic and geometrical structures of 3d-metal monocarbonyls MCO (M=Sc to Cu), the MCO − anions and MCO + cations are computed using the density functional theory with generalized gradient approximation for the exchange-correlation potential.
Abstract: The electronic and geometrical structures of 3d-metal monocarbonyls MCO (M=Sc to Cu), the MCO − anions and MCO + cations are computed using the density functional theory with generalized gradient approximation for the exchange-correlation potential. Our calculated adiabatic electron affinities and ionization potentials are in good agreement with experiment. Using the results of our previous computations on the MC, MC − , and MC + series, we estimated the energies required for the Boudouard disproportionation reactions MCO 0,−,+ +CO→MC 0,−,+ +CO 2 . Among the neutrals, this reaction is endothermic by 1.30 eV for Mn, while Fe is found to be the second best atom, with the reaction being endothermic by 1.59 eV. These are substantially reduced with respect to the gas phase Boudouard reaction CO+CO→C+CO 2 , which is endothermic by 5.65 eV. Several of the anions have disproportionation energies similar to the neutrals, while cations are found to be less favorable than the neutrals.
27 citations
TL;DR: A coordination sphere model in which CUO in solid neon is initially solvated by four or more Ne atoms is suggested, which suggests a crossover from a singlet ground state to a triplet ground state.
Abstract: Laser-ablated U atoms co-deposited with CO in excess neon produce the novel CUO molecule, which forms distinct Ng complexes (Ng=Ar, Kr, Xe) with the heavier noble gases. The CUO(Ng) complexes are identified through CO isotopic and Ng reagent substitution and comparison to results of DFT frequency calculations. The U[bond]C and U[bond]O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from neon matrix (1)Sigma(+) CUO values, which indicates a (1)A' ground state for the CUO(Ng) complexes. The CUO(Ng)(2) complexes in excess neon are likewise singlet molecules. However, the CUO(Ng)(3) and CUO(Ng)(4) complexes exhibit very different stretching frequencies and isotopic behaviors that are similar to those of CUO(Ar)(n) in a pure argon matrix, which has a (3)A" ground state based on DFT vibrational frequency calculations. This work suggests a coordination sphere model in which CUO in solid neon is initially solvated by four or more Ne atoms. Up to four heavier Ng atoms successively displace the Ne atoms leading ultimately to CUO(Ng)(4) complexes. The major changes in the CUO stretching frequencies from CUO(Ng)(2) to CUO(Ng)(3) provides evidence for the crossover from a singlet ground state to a triplet ground state.
TL;DR: In this paper, the Group 15 MH2 dihydride radicals and the MH3 trihydrides are observed for Sb and Bi metals, and no evidence is found for thermochemically unstable BiH5 molecule.
Abstract: Laser-ablated Sb and Bi atoms react with hydrogen during condensation in excess hydrogen, neon, and argon to form the SbH and BiH diatomic molecules. In addition the new Group 15 MH2 dihydride radicals and the MH3 trihydrides are observed for Sb and Bi metals. Although BiH3 is of limited stability in the gas phase, BiH3 is formed by further H atom reactions with BiH2 in solid hydrogen and neon. No evidence is found for the thermochemically unstable BiH5 molecule.
TL;DR: In this article, laser-ablated Mo and W atoms react with CO in excess neon to give the same unsaturated M(CO) 3, 4, 5 carbonyls observed from photodissociation of M( CO) 6.
Abstract: Laser-ablated Mo and W atoms react with CO in excess neon to give the same unsaturated M(CO) 3 , 4 , 5 carbonyls observed from photodissociation of M(CO) 6 . The observed neon matrix fundamentals for these M(CO) 3 , 4 , 5 species bridge previous argon matrix and gas phase values. The M(CO) 2 dicarbonyls absorb at 1895.2 and 1884.5 cm - 1 , and the MCO monocarbonyls absorb at 1881.2 and 1859.9 cm - 1 for Mo and W, respectively. The M(CO) 1 , 2 + cations and M(CO) 1 , 2 - anions are observed as the ablation process also provides cations and electrons. Density functional theory calculations support the product identifications and vibrational assignments.