Showing papers by "Lester Andrews published in 1998"
TL;DR: In this paper, the infrared spectra of Ni(CO)1-4 complexes with 12C16O, 13C 16O, and 12C18O substitution were analyzed and shown to be isotopic.
Abstract: Laser-ablated Ni atoms and electrons react with CO in excess argon during condensation to form the Ni(CO)1-4 complexes and Ni(CO)1-3- anions. Matrix infrared spectra of the neutral complexes with 12C16O, 13C16O, and 12C18O substitution are in agreement with earlier reports with thermal Ni atoms. In addition, new absorptions at 1847.0, 1801.7, and 1858.8 cm-1 exhibit isotopic spectra in excellent agreement with DFT calculations for the Ni(CO)1-3- anions. An experiment doped with the CCl4 electron-trapping molecule gave the same Ni(CO)1-4 spectrum without the corresponding anions, which strongly supports this identification of the molecular anions.
84 citations
TL;DR: In this article, the valence angles of the metal dioxide molecules were estimated to be 108 ± 5° for NbO2 and 106 ± 5¼ for TaO2.
Abstract: Laser-ablated niobium and tantalum atoms react with O2 to give MO, MO2, MO2-, and MO2+ products, which are identified from oxygen isotopic substitution on their matrix infrared spectra and from DFT calculations of isotopic frequencies. Annealing allows diffusion and further reaction to form (O2)MO2 complexes, which are characterized by four fundamentals. On the basis of the ν3 vibrational frequencies for the M16O2 and M18O2 isotopic molecules, the metal dioxide valence angles are estimated to be 108 ± 5° for NbO2 and 106 ± 5° for TaO2; the molecular cations have the smaller valence angles 103 ± 5° and 105 ± 5° for NbO2+ and TaO2+, respectively, and the molecular anions are more open with 120 ± 10° valence angles. Evidence is also presented for stable MO3- anion species.
78 citations
TL;DR: In this article, the FeCO molecule is observed at 19220 cm−1 in solid argon based on concentration studies, isotopic shifts, and density functional theory frequency calculations; the argon matrix redshifts this band 270 cm− 1 (14%) from the high-resolution gas phase measurement.
Abstract: Laser-ablated iron atoms have been reacted with CO molecules during condensation in excess argon The FeCO molecule is observed at 19220 cm−1 in solid argon based on concentration studies, isotopic shifts, and density functional theory frequency calculations; the argon matrix redshifts this band 270 cm−1 (14%) from the high-resolution gas phase measurement Absorptions at 18792 and 19848 cm−1 are assigned from isotopic substitution and density functional theory frequency calculations to the antisymmetric and symmetric vibrations of a bent Fe(CO)2 molecule in the matrix The Fe(CO)x (x=3,4,5) molecules are also observed on annealing in agreement with earlier matrix work Iron carbonyl ions were also produced and trapped: photosensitive absorptions at 17703, 17219, 18150, 17865, and 18535 cm−1 are assigned to FeCO−, Fe(CO)2−, Fe(CO)3−, and Fe(CO)4−, respectively, and a weak photosensitive 20815 cm−1 band is assigned to FeCO+ Polynuclear metal carbonyls were also formed on annealing; based on different CO concentration and laser power experiments and isotopic substitution, an 18977 cm−1 absorption is assigned to Fe2CO and a 19485 cm−1 band to Fe3CO
72 citations
TL;DR: In this article, the strong antisymmetric fundamental of isolated O4− at 953.5±0.3 cm−1 in solid argon from the capture of ablated electrons by O2 followed by the addition of another O2 molecule.
Abstract: Laser ablation of metal targets in front of condensing Ar/O2 mixtures produced the strong antisymmetric fundamental of isolated O4− at 953.5±0.3 cm−1 in solid argon from the capture of ablated electrons by O2 followed by the addition of another O2 molecule. The sharp sextet mixed isotopic spectrum suggests a structure with two equivalent O2 subunits and equivalent atomic positions in each subunit. DFT/UB3LYP calculations reveal doublet trans and rectangular structures with the latter more stable by 8.8 kcal/mol. Of more importance, the mixed oxygen isotopic spectrum calculated for the rectangular structure matches the observed spectrum much better than values calculated for the trans structure; thus, it is concluded that isolated O4− probably has an approximately rectangular structure. It is further suggested that the earlier observed alkali metal M+O4− species have rectangular pyramidal structures and that the sharp 954±1 cm−1 bands attributed to a different structural isomer are in fact due to the isolated anion owing to photoionization of the alkali metal atoms by radiation from the Nernst glower source of the grating spectrophotometer.
70 citations
TL;DR: In this paper, photoisomerization to form the novel side-bonded OSc-(η2-CO) isomer and photoionization to the OScCO+ cation and OScOC+ and ScOCO+ isomers proceed upon different wavelength photolyses.
Abstract: Laser-ablated Sc atoms react with CO2 molecules to give primarily the insertion product, OScCO, and a minor amount of the addition product, Sc-(η2-OC)O, which have been isolated in a solid argon matrix. Photoisomerization to form the novel side-bonded OSc-(η2-CO) isomer and photoionization to the OScCO+ cation and OScOC+ and ScOCO+ isomers proceed upon different wavelength photolyses. The product absorptions were identified by isotopic substitution and density functional calculations of isotopic frequencies. Similar experiments with Y give spectra for the analogous product molecules and cations.
66 citations
TL;DR: In this paper, laser-ablation of over 20 different metal targets with concurrent 10 K codeposition of Ar/NO mixtures produces metal independent infrared bands at 1589.3 cm−1 due to (NO)2+, a new absorption at 1221.0cm−1, and a band set at 1300.3, 1222.7, 884.4
Abstract: Laser-ablation of over 20 different metal targets with concurrent 10 K codeposition of Ar/NO mixtures produces metal independent infrared bands at 1589.3 cm−1 due to (NO)2+, a new absorption at 1221.0 cm−1, and a band set at 1300.3, 1222.7, 884.4 cm−1. The latter bands decrease more on annealing than the 1221.0 cm−1 band. Isotopic substitution (14NO,15NO, 15N18O, and mixtures) shows that these new vibrations involve two equivalent N–O oscillators, which identifies two new (NO)2 species. The excellent agreement with frequencies, intensities, and isotopic frequency ratios from density functional theory calculations substantiates assignment of the 1221.0 cm−1 band to trans-(NO)2− and the three band set to cis-(NO)2−. The observation of a weak combination band at 2492.0 cm−1 further substantiates assignment of the two N–O stretching modes in cis-(NO)2−
52 citations
TL;DR: In this paper, the results of laser-ablated thorium and uranium metals in condensing pure dinitrogen streams as well as argon/dinitrogen mixtures have provided spectroscopic evidence for the presence of several previously uncharacterized actinide metal nitrides and dinitrogens complexes.
Abstract: The reactions of laser-ablated thorium and uranium metals in condensing pure dinitrogen streams as well as argon/dinitrogen mixtures have provided spectroscopic evidence for the presence of several previously uncharacterized actinide metal nitrides and dinitrogen complexes. Infrared spectra of the matrix isolated product species indicate that thorium and uranium atoms have a significant bond weakening effect on dinitrogen upon initial complexation and in some cases complete dinitrogen bond cleavage is observed. In the reactions of laser-ablated thorium and uranium atoms with pure dinitrogen, the primary products are the metal mononitride (M-N), the metal dinitride (N–M–N), and in the uranium reactions, two dinuclear products U(μ-N)2U and NU(μ-N)2U. In the reactions of thorium with dinitrogen in argon, the primary products are N–Th–N, Th(μ-N)2Th, and the dinitrogen complexes Th-η1-N2 and Th-η1:η1-(N2)2. The complete ground-state electronic structure and vibrational spectrum of each product molecule has bee...
52 citations
TL;DR: In this paper, density functional theory (DFT) calculations predict quintet and quartet ground states for CoN and NiN, respectively, and frequencies in reasonable agreement with the observed values.
Abstract: Laser-ablated Co and Ni atoms, co-deposited with pure nitrogen at 10 K, gave a strong new 795.3 cm-1 band with cobalt and a 838.8, 836.1 cm-1 isotopic doublet (2.5/1.0) with nickel, which exhibited 14/15 isotopic ratios appropriate for the diatomic CoN and NiN molecules. In solid argon, CoN absorbs at 826.5 cm-1 and gives way on annealing to bands at 795.8 and 792.0 cm-1, which are due to (NN)xCoN complexes. Density functional theory (DFT) calculations predict quintet and quartet ground states for CoN and NiN, respectively, and frequencies in reasonable agreement with the observed values. Evidence is also presented for the dimetal dinitrides, (CoN)2 and (NiN)2, with rhombus structures and metal−metal bonding across the ring. DFT-based calculations and revised assignments are presented for Ni−NN stretching modes in the dinitrogen complexes.
39 citations
TL;DR: In this paper, laser-ablated niobium, tantalum, and rhenium atoms have been reacted with nitrogen atoms and molecules during condensation in excess argon and in pure nitrogen gas.
Abstract: Laser-ablated niobium, tantalum, and rhenium atoms have been reacted with nitrogen atoms and molecules during condensation in excess argon and in pure nitrogen gas. Metal nitride molecules NbN, TaN, ReN, and their dinitrogen complexes were trapped and identified by nitrogen isotopic shifts and DFT frequency calculations. The NbN2 and TaN2 dinitride molecules were produced on annealing in solid nitrogen and on deposition and increased on photolysis in solid argon. Metal dinitrogen complexes were also observed for each metal.
37 citations
TL;DR: In this paper, laser-ablated molybdenum and tungsten atoms were reacted with dioxygen and 18O-substituted DIOYGEN and the products of these reactions were isolated in solid argon matrices at 10 K and studied by matrix infrared spectroscopy.
Abstract: Laser-ablated molybdenum and tungsten atoms were reacted with dioxygen and 18O-substituted dioxygen. The products of these reactions were isolated in solid argon matrices at 10 K and studied by matrix infrared spectroscopy. Analysis of spectra enabled identification of reaction products, which included MoO2, (O2)MoO2, MoO3, WO, WO2, (O2)WO2, and WO3. Resolution of isotopic splitting due to natural isotopic abundance of the metal verified the presence of a single metal atom in these molecules and allowed for calculation of bond angles for the molybdenum and tungsten dioxide molecules and their dioxygen complexes.
37 citations
TL;DR: In this article, the first experimental evidence for the fluoride Grignard species, CH3MgF, was reported, and the secondary reaction products MgX, MgMgX 2, MgH 2, MGX, MGX2, MGH2, MGH3 and MGX were identified by isotopic (13C, D, and 26Mg) substitution and correlation with B3LYP and BP86 isotopic frequency calculations.
Abstract: Magnesium atoms generated by laser ablation were reacted with methyl halides diluted (0.5% to 0.1%) in argon. Reaction products were trapped in a cryogenic argon matrix and analyzed by infrared spectroscopy. The primary reaction product, isolated Grignard molecule CH3MgX, and the secondary reaction products MgX, MgX2, MgH, MgH2, CH4, C2H6, CH2X, CH3MgCH3, XMgCH2, HMgCH3, and HMgCH2X were identified by isotopic (13C, D, and 26Mg) substitution and by correlation with B3LYP and BP86 isotopic frequency calculations. This investigation reports the first experimental evidence for the fluoride Grignard species, CH3MgF. Infrared absorptions were also observed for associated Grignard species.
TL;DR: In this article, the BC2H3 closed-shell isomers borirene (CH)2BH, ethynylborane H2BCCH, and borallene HBCCH2 have been identified from infrared spectra by using 10B, 13C, and D substitution and BP86/6-311G* isotopic frequency calculations.
Abstract: Laser-ablated boron atoms have been reacted with ethylene during condensation in excess argon. The BC2H3 closed-shell isomers borirene (CH)2BH, ethynylborane H2BCCH, and borallene HBCCH2 have been identified from infrared spectra by using 10B, 13C, and D substitution and BP86/6-311G* isotopic frequency calculations. The observation of both cyclic aromatic and aliphatic products suggests that the reaction proceeds through both exothermic CC addition and C−H insertion reaction mechanisms. Evidence is presented for the most stable BC2H4 radicals, namely, and aliphatic H2BCCH2, which require H-atom migration within the intermediates first formed. Ethane gave a smaller yield of the same products, including linear HBCC and BCCH, vinylborane H2BC2H3, and an enhanced yield of the C−C insertion product CH3BCH2.
TL;DR: In this article, the absorption of chromium atoms with NO molecules during condensation in excess argon has been studied and identified via isotopic substitution and DFT frequency calculations, where the insertion reaction to give the more stable NCrO product requires activation energy, while the addition products Cr−η1-NO and Cr− η2-NO can be formed on diffusion of cold reagents in solid argon.
Abstract: Laser-ablated chromium atoms have been reacted with NO molecules during condensation in excess argon. Absorptions due to NCrO (976.1, 866.2 cm-1), Cr−η1-NO (1614.3, 541.1 cm-1), and Cr−η2-NO (1108.8, 528.2,478.0 cm-1) are observed and identified via isotopic substitution and DFT frequency calculations. The insertion reaction to give the more stable NCrO product requires activation energy, while the addition products Cr−η1-NO and Cr−η2-NO can be formed on diffusion of cold reagents in solid argon. Higher nitrosyls are also formed on annealing. On the basis of isotopic multiplets, a 1623.3 cm-1 absorption is assigned to Cr−(η1-NO)2, a 1663.5 cm-1 absorption to Cr−(η1-NO)3, and absorptions at 1726.0, 663.0, and 506.1 cm-1 are assigned to Cr−(η1-NO)4. Evidence is also presented for the Cr−(η1-NO)x- anions (x = 1, 2, 3) absorbing 100−160 cm-1 lower than the neutral nitrosyl counterparts. In addition, NO complexes with CrO and CrO2 are also observed.
TL;DR: In this paper, the same saturated (YN)2(NN)x and (LaN)2 (NN)2)x dinitrogen complexes are prepared on annealing solid argon containing 2% N2 and deposition in pure nitrogen.
Abstract: Laser-ablated Y and La atoms react with nitrogen to produce metal nitrides and dinitrogen complexes, whereas thermally evaporated Y and La atoms form only dinitrogen complexes. The ligated mononitride complexes (NN)xYN and (NN)xLaN at 771.6 and 761.7 cm-1 in solid nitrogen are identified from nitrogen-15 shifts. These complexes predict gas-phase fundamentals near 800 and 790 cm-1 respectively for YN and LaN. The (YN)2 and (LaN)2 molecules and dinitrogen complexes are also identified from nitrogen-15 shifts and result from the reaction of two metal atoms with a single dinitrogen molecule involving the Y(N2) and La(N2) intermediate species. The same saturated (YN)2(NN)x and (LaN)2(NN)x dinitrogen complexes are prepared on annealing solid argon containing 2% N2 and deposition in pure nitrogen. The growth of ligated (YN)2(NN)x and (LaN)2(NN)x on annealing suggests that this nitrogen fixation reaction involves little activation energy.
TL;DR: In this paper, the first part of a systematic study of small nitride molecules and simple dinitrogen complexes of the lanthanide metals except promethium was presented, and several reaction pathways to formation of the small nitrides have been explored.
Abstract: This paper summarizes the first part of a systematic study of the small nitride molecules and simple dinitrogen complexes of the lanthanide metals except promethium. Simple nitrides of the general formulas LnN and (LnN)2 have been identified for Ln = Ce, Pr, Nd, Sm, Eu, and Gd; LnN2 has been identified for Ln = Ce, Pr, Nd, and Sm. Several dinitrogen complexes of the type Ln(N2), Ln(NN), Ln(NN)2, and Ln(NN)x have also been observed in matrix infrared investigations. The tendency of the identified nitrides to complex dinitrogen is readily determined from experimental data, which provide frequencies for observed fundamentals both before and after dinitrogen complexation. Several reaction pathways to formation of the small nitrides have been explored. The favored pathway to the (LnN)2 molecule involves reduction of N2 by two Ln metal atoms concurrent with complete scission of the N≡N triple bond.
TL;DR: In this paper, laser-ablated cobalt atoms have been reacted with CO molecules during condensation in excess argon, and the CoCO molecule was observed after deposition, and Co(CO)2,3,4 are formed on annealing in agreement with earlier matrix work.
Abstract: Laser-ablated cobalt atoms have been reacted with CO molecules during condensation in excess argon. The CoCO molecule is observed after deposition, and Co(CO)2,3,4 are formed on annealing in agreement with earlier matrix work. Cobalt carbonyl anions are also produced and trapped. On the basis of isotopic substitution and density functional calculations, a sharp absorption at 1804.0 cm-1 is assigned to the C−O stretching mode of CoCO-, 1768.9 and 1860.2 cm-1 bands to antisymmetric and symmetric C−O stretching vibrations of bent Co(CO)2-, and 1826.9 and 1890.0 cm-1 absorptions to the antisymmetric stretching modes of Co(CO)3- and Co(CO)4-, respectively.
TL;DR: In this article, the vibrational frequencies of several states of CaO2, ScO2 and TiO2 are computed using density functional theory (DFT), the Hartree-Fock approach, second-order Moller-Plesset perturbation theory (MP2), and the complete-active-space self-consistent field theory.
Abstract: The vibrational frequencies of several states of␣CaO2, ScO2, and TiO2 are computed using density functional theory (DFT), the Hartree-Fock approach, second-order Moller-Plesset perturbation theory (MP2), and the complete-active-space self-consistent-field theory. Three different functionals are used in the DFT calculations, including two hybrid functionals. The coupled cluster singles and doubles approach including the effect of connected triples, determined using perturbation theory, is applied to selected states. The Becke-Perdew 86 functional appears to be the most cost-effective method of choice, although even this functional does not perform well for one state of CaO2. The MP2 approach is significantly inferior to the DFT approaches.
TL;DR: In this paper, the authors identified the dimetal dinitride (ScN)2 molecules by nitrogen-15 substitution and density functional calculations. But they were not able to obtain the vibrational frequencies that help support the identification of these new molecules.
01 May 1998
TL;DR: Theoretical study using selfconsistent field (SCF), hybrid density functional theory (B3LYP) and quadratic configuration interaction including single and double excitations (QCISD) with the Dunning correlation consistent polarized valence double zeta (cc-pVDZ) basis set have been used to examine the structures and vibrational properties of the singlet species with BC 2 H 3 stoichiometry.
Abstract: Theoretical study using self-consistent field (SCF), hybrid density functional theory (B3LYP) and quadratic configuration interaction including single and double excitations (QCISD) with the Dunning correlation consistent polarized valence double zeta (cc-pVDZ) basis set have been used to examine the structures and vibrational properties of the singlet species with BC 2 H 3 stoichiometry. Relative stabilities are estimated at the CCSD(T)/cc-pVTZ level using QCISD/cc-pVDZ optimized geometries. Five species corresponding to different nuclear arrangements have been studied. The absolute minimum corresponds to the 2 π aromatic borirene molecule (HBC 2 H 2 with a BC 2 ring). Ethynylborane (H 2 BCCH, C 2 v ) and borallene (H 2 CCBH, C 2 v ) are respectively 6.4 and 24.3 kcal/mol higher. Vinylborine (C 2 H 3 B, C s ) and H 2 CBCH (C 2 v ) are much less stable, 46.2 and 49.1 kcal/mol respectively higher than borirene. The calculated vibrational spectra agree with experiment and confirm the infrared matrix characterization of the three most stable species.
TL;DR: In this article, the reaction of thermal and laser-ablated Mn atoms with NO produces the Mn−(η 1-NO)x complexes (x = 1−3), a series of η 2 complexes, and in addition, laser ablated Mn gives the NMnO insertion product.
Abstract: Reactions of thermal and laser-ablated Mn atoms with NO produce the Mn−(η1-NO)x complexes (x = 1−3), a series of η2 complexes, and in addition, laser-ablated Mn gives the NMnO insertion product. Th...
TL;DR: In this article, photolysis markedly increases (N2)(NbO2) and (N 2)(TaO2), which are stable end products for these reactions, which are identified from isotopic substitution and density functional calculations of isotopic frequencies.
Abstract: Laser-ablated Nb and Ta atoms react with NO to give primarily the NNbO and NTaO insertion products, which are identified from isotopic substitution and density functional calculations of isotopic frequencies. Although the mononitrosyls are not observed, annealing gives dinitrosyls the trinitrosyls for both metals. Photolysis markedly increases (N2)(NbO2) and (N2)(TaO2), which are stable end products for these reactions.
TL;DR: In this article, the isotopic frequency ratios characterize different normal modes, and these are uniquely matched to the stretching modes of triplet AlON (1282.1, 566.7 cm-1) and triplet NAlO (1644.3, 510.2 cm-2) by density functional theory (DFT) isotope frequency calculations.
Abstract: Laser-ablated aluminum atoms have been reacted with NO, 15NO, and 15N18O during condensation in excess argon using a variety of concentrations and laser energies/cm2. Four of the five major product absorptions with higher laser energy were also observed with lower laser energy. The isotopic frequency ratios characterize different normal modes, and these are uniquely matched to the stretching modes of triplet AlON (1282.1, 566.7 cm-1) and triplet AlNO (1644.3, 510.2 cm-1) by density functional theory (DFT) isotopic frequency calculations. The fifth band (1079.5 cm-1) is due to a terminal Al−O stretching mode that is consistent with triplet NAlO based on DFT isotopic frequency calculations. The total product yield depended on laser energy; both AlON and AlNO addition products were produced with lower energy, but the insertion product NAlO required higher energy. Anions were favored with lower laser energy, and a weak 1380.6 cm-1 band is assigned to AlNO- in accord with DFT isotopic frequency calculations.