Showing papers by "Lester Andrews published in 2000"

Infrared Spectra of UO2, UO2+, and UO2- in Solid Neon

Abstract: Reactions of laser-ablated uranium atoms, cations, and electrons with O2 during condensation with excess neon produce UO, UO2, UO3, UO2+, and UO2- as characterized by infrared spectra with oxygen isotopic substitution and B3LYP/pseudopotential calculations. Differences in low-lying states for UO2 give rise to substantial shifts and ground state reversal between argon and neon matrices. A series of B3LYP/pseudopotential calculations has been undertaken on oxide species related to the uranyl dication by the addition of one, two, or three electrons. Several electronic states have been characterized for each species. These simple, low-cost calculations predict vibrational frequencies which match those observed in neon matrices extremely well (typically 3−5% too high). The ground state of neutral UO2 appears to have 3Φu symmetry, while 2Φu ground states are implied for UO2+ and UO2-.

Reactions of Laser-Ablated Ni, Pd, and Pt Atoms with Carbon Monoxide: Matrix Infrared Spectra and Density Functional Calculations on M(CO)n (n = 1−4), M(CO)n- (n = 1−3), and M(CO)n+ (n = 1−2), (M = Ni, Pd, Pt)

Abstract: Laser-ablated Ni, Pd, and Pt atoms have been reacted with CO molecules followed by condensation in excess neon at 4 K. Besides the neutral metal carbonyl species, metal carbonyl anions [M(CO)n- (n ...

Reactions of Laser-Ablated Ag and Au Atoms with Carbon Monoxide: Matrix Infrared Spectra and Density Functional Calculations on Ag(CO)n (n = 2, 3), Au(CO)n (n = 1, 2) and M(CO)n+ (n = 1−4; M = Ag, Au)

Abstract: Laser-ablated Ag and Au atoms have been reacted with CO molecules followed by condensation in excess neon at 4 K. Besides the neutral carbonyls [Ag(CO)n (n = 2, 3), Au(CO)n (n = 1, 2), Au2(CO)2], the metal carbonyl cations [M(CO)n+ (n = 1−4)] have been formed and identified. The CO concentration, isotopic substitution and CCl4 doping experiments confirm the identification of the cationic species. Excellent agreement between observed bands and frequencies and isotopic frequency ratios from the DFT calculations support the vibrational assignments and identification of the metal carbonyl complexes.

Reactions of Laser-Ablated Aluminum Atoms with Nitrogen Atoms and Molecules. Infrared Spectra and Density Functional Calculations for the AlN2, Al2N, Al2N2, AlN3, and Al3N Molecules

Abstract: Laser-ablated aluminum atoms react with dinitrogen on condensation at 10 K to form N3 radical and the subject molecules, which are identified by nitrogen isotopic substitution, further reactions on annealing, and comparison with isotopic frequencies computed by density functional theory. The major AlN3 product is identified from three fundamentals and a statistically mixed nitrogen isotopic octet pattern. The aluminum rich Al2N and Al3N species are major products on annealing to allow diffusion and further reaction of trapped species. This work provides the first experimental evidence for molecular AlxNy species that may be involved in ceramic film growth.

Reactions of Laser-Ablated U and Th with CO2: Neon Matrix Infrared Spectra and Density Functional Calculations of OUCO, OThCO, and Other Products

Abstract: Laser-ablated U and Th atoms react with CO2 to give OUCO (1806.9, 823.2 cm-1) and OThCO (1778.4 cm-1) as major products, which are identified by isotopic substitution (13CO2, C18O2 and 12CO2 + 13CO2, C16O18O + C18O2 mixtures), doping with CCl4 as an electron trap, and comparison with frequencies from density functional calculations. The insertion reaction is spontaneous as these bands increase on annealing the neon matrix from 4 to 6 K. Further reaction of OAnCO (An = Th, U) with another CO2 molecule gives the O2An(CO)2 product, although much more so with uranium than thorium. Reaction of the metal cations with CO2 produces OUCO+ (2073.0, 881.2 cm-1) and OThCO+ (2009.9, 896.4 cm-1) with higher yield in thorium experiments. The O2An(CO)2- anions are observed for both metals again with higher yield in uranium investigations.

Reactions of Laser-Ablated Ga, In, and Tl Atoms with Nitrogen Atoms and Molecules. Infrared Spectra and Density Functional Calculations of GaN, NGaN, NInN, and the M3N and MN3 Molecules

Abstract: Laser-ablated gallium atoms react with nitrogen atoms and molecules to give GaN, NGaN, Ga3N, and GaN3, which are identified from nitrogen and gallium isotopic shifts, mixed isotopic splittings, and density functional theory calculations. A 484.9 cm-1 band is assigned to the GaN molecule perturbed by the nitrogen matrix, sharp 586.4 and 584.1 cm-1 bands to the antisymmetric vibration of the linear N69GaN and N71GaN molecules, 666.2 and 656.0 cm-1 bands to the planar Ga3N molecule, and 2096.9 and 1328.3 cm-1 bands to antisymmetric and symmetric N−N−N vibrations of the GaNNN azide molecule. This work provides the first experimental evidence for GaxNy molecules that may be involved in semiconductor film growth. Laser-ablated In and Tl atom reactions produce analogous molecules.

Reactions of Laser-Ablated Fe, Co, and Ni with NO: Infrared Spectra and Density Functional Calculations of MNO+and M(NO)x(M = Fe, Co,x= 1-3; M = Ni,x= 1, 2), and M(NO)x-(M = Co, Ni;x= 1, 2)

Abstract: Laser-ablated iron, cobalt, and nickel atoms, cations, and electrons have been reacted with NO molecules during condensation in excess neon and argon. The end-on bonded Fe(NO)1-3, Co(NO)1-3, and Ni(NO)1-2 nitrosyls and side-bonded Fe−(η2-NO), Co−(η2-NO), and Ni−(η2-NO) species are formed during sample deposition or on annealing. The FeNO+, CoNO+, and NiNO+ mononitrosyl cations are also produced via metal cation reactions with NO. Evidence is also presented for the Ni(NO)1,2- and Co(NO)1,2- anions. The product absorptions are identified by isotopic substitution (15N16O, 15N18O, and mixtures), electron trapping with added CCl4, and density functional calculations of isotopic frequencies. This work provides the first vibrational spectroscopic characterization of Fe, Co, and Ni nitrosyl cations and anions.

Infrared Spectra and Density Functional Calculations of MO2, MO3, (O2)MO2, MO4, MO2-(M = Re, Ru, Os) and ReO3-, ReO4-in Solid Neon and Argon†

Abstract: Laser-ablated rhenium, ruthenium, and osmium atoms react with O2 in excess neon and argon during condensation to form the MO2 dioxide molecules as major products. The MO3 trioxides with D3h symmetr...

Reactions of Laser-Ablated Cu with NO: Infrared Spectra and Density Functional Calculations of CuNO+, CuNO, Cu(NO)2, and Cu(NO)2- in Solid Neon and Argon

Abstract: Laser-ablated copper atoms react with NO molecules in excess neon and argon during condensation to form the CuNO and Cu(NO)2 complexes as major products and Cu(NO)2(NO)* as a minor product. In addition, the CuNO+ cation and Cu(NO)2- anion are also formed. The product absorptions are identified from isotopic shifts and splitting patterns in the matrix infrared spectra and are supported by DFT calculations of isotopic frequencies. Sequential annealing increases CuNO and Cu(NO)2, and then CuNO gives way to Cu(NO)2 and Cu(NO)2(NO)*, a dinitrosyl with a third inequivalent NO subgroup. The isolated mononitrosyl and dinitrosyl species provide a scale to estimate local charge on CuNO and Cu(NO)2 sites in Cu-exchanged zeolite catalyst systems.

Ground‐State Reversal by Matrix Interaction: Electronic States and Vibrational Frequencies of CUO in Solid Argon and Neon

Abstract: The reactions of laser-ablated metal atoms with small molecules during their condensation in frozen noble gas matrices have led to a remarkable number of fundamental small molecules that provide new insights into the structures of and bonding in metal complexes.

Reactions of Zirconium and Hafnium Atoms with CO: Infrared Spectra and Density Functional Calculations of M(CO)x, OMCCO, and M(CO)2- (M = Zr, Hf; x = 1−4)

Abstract: Laser-ablated zirconium and hafnium atoms were reacted with CO molecules during condensation in excess neon. The Zr(CO)x and Hf(CO)x (x = 1−4) carbonyls formed during sample deposition or on anneal...

Characterization of the Reaction Products of Laser-Ablated Lanthanide Metal Atoms with Molecular Hydrogen. Infrared Spectra of LnH, LnH2, LnH3, and LnH4 Molecules in Solid Argon

Abstract: Infrared spectra of representative LnH1-4 lanthanide hydride molecules are observed in solid argon following reactions of the laser-ablated metal atoms with H2. The LnH2 dihydride is the major product and a stable (H2)LnH2 complex is observed for Ce and Pr. In addition, bands are also assigned to bridging hydrogen motions of several (LnH)2 dimers. Supplementary density functional calculations of the lanthanide hydride reaction products reproduce general features of the spectra. Spectra of isolated molecular EuH2 and solid stoichiometric EuH2 reveal close correspondence, lending support to the molecular assignment and, by extrapolation, providing benchmark infrared frequencies for other lanthanide hydride solids based on their respective molecular vibrational modes.

Matrix Infrared Spectra and Density Functional Calculations of Manganese and Rhenium Carbonyl Neutral and Anion Complexes

Abstract: Laser-ablated Mn and Re atoms and electrons react with CO upon co-condensation in excess argon and neon to produce carbonyl neutrals and anions. These species are identified through isotopic substitution, CCl4 doping to trap ablated electrons, and density functional theory isotopic frequency calculations. MnCO is identified at 1933.6 cm-1 in argon and at 1950.7 cm-1 in neon, which are in agreement with the gas phase 1955 ± 15 cm-1 photoelectron measurement. MnCO- is found at 1789.4 cm-1 in argon and 1807.5 cm-1 in neon. The Mn(CO)2 and Re(CO)2 dicarbonyls are major product absorptions. Annealing to allow further reaction of CO produces higher carbonyls including Mn2(CO)10 and Re2(CO)10 in solid argon. Argon and neon matrix experiments are compared for both metals.

Reactions of Laser-Ablated Osmium and Ruthenium Atoms with Nitrogen. Matrix Infrared Spectra and Density Functional Calculations of Osmium and Ruthenium Nitrides and Dinitrides

Abstract: Laser-ablated osmium and ruthenium atoms were reacted with nitrogen molecules; the products were isolated in solid argon and nitrogen and identified by infrared spectroscopy. Both MN and NMN nitrides are observed, and estimates for the triatomic bond angles are made using nitrogen and ruthenium isotopic data. The growth of NOsN on annealing in solid argon suggests that osmium atoms insert into the dinitrogen triple bond at cryogenic temperatures, allowing a lower limit of ∼473 kJ/mol to be estimated for the average Os−N bond energy in NOsN. The force constants for MN and NMN (M= Fe, Ru, Os) were calculated using all available isotopic data; force constants increase moving down the metal group, and diatomic MN force constants are larger than those for the corresponding NMN triatomic molecules. DFT calculations for the ruthenium and osmium nitrides give reasonable agreement with experiment. Bonding analyses for these molecules show that the M−N bonds are largely nonpolar with bond orders in the range 2.5−3....

Reactions of Co, Ni, and Cu Atoms with CS2: Infrared Spectra and Density-Functional Calculations of SMCS, M-(η2-CS)S, M-CS2, and MCS2+in Solid Argon

Abstract: Laser-ablated cobalt, nickel, and copper atoms and cations were reacted with CS2 molecules during condensation in excess argon. The carbon-bonded M−η1-CS2 and side-bonded M−(η2-CS)S complexes were formed on annealing, whereas the inserted SMCS molecules were formed on photolysis. The Co−η1-CS2+, Ni−η1-CS2+ and Cu−SCS+ cations were also produced by metal cation reactions with CS2. The product absorptions are identified by isotopic substitutions, electron trapping with added CCl4, and density functional calculations. This work provides the first vibrational spectroscopic characterization of the Co, Ni, and Cu−CS2 neutral and cation complexes and the SMCS insertion products.

Manganese Carbonyl Nitrosyl Complexes in Solid Argon: Infrared Spectra and Density Functional Calculations

Abstract: Laser-ablated manganese atoms react with CO and NO mixtures upon condensation in excess argon and further annealing to produce a series of unsaturated manganese carbonyl nitrosyl complexes including Mn(CO)(NO), Mn(CO)(NO)2, and Mn(CO)2(NO). The Mn(CO)(NO) complex isomerizes to Mn(CO)(η2-NO) on visible photolysis, which rearranges to the isocyanate OMnNCO molecule on ultraviolet photolysis. The Mn(CO)(NO)(η2-NO) and Mn(CO)(NO)2(η2-NO) isomers also appear on annealing as does Mn(CO)4(NO). The major product after annealing is the stable 18-electron molecule Mn(CO)(NO)3. The observed absorption bands of reaction products were identified by isotopic substitution (13C16O, 15N16O, 15N18O, and mixtures) and reproduced within 1−3% by density functional theory calculations of vibrational fundamentals. The bonding and reaction mechanisms are discussed. The isocyanate species formed here from the simple Mn(CO)(NO) complex is relevant to catalytic reactions for pollution control.

Matrix infrared spectroscopic study of magnesium carbene and carbenoid radicals and analysis of their bonding with density functional calculations.

Abstract: Magnesium atoms generated by laser ablation were reacted with methyl halides and methane diluted in argon. Among the reaction products were the metal carbene species, MgCH2, and carbenoid radicals, XMgCH2 (where X = H, F, C1, and Br). This investigation reports matrix infrared spectra for Mg carbene and carbenoid species in a cold matrix, and electronic structure calculations for these and related beryllium species. An unusual bonding interaction for the MCH2 species is described in which the bonding in the α and β manifolds is qualitatively different. Vibrational frequencies and analysis of the results of density functional calculations provide information about the nature of the bonding in these species and allow for a comparison to the well-known transition metal Fischer- and Schrock-type carbene complexes. The special difficulties of computational modeling of vibrations in highly polar molecules are discussed.

Reactions of Laser-Ablated Palladium and Platinum Atoms with Nitric Oxide: Infrared Spectra and Density Functional Calculations of MNO+,0,- and M(NO)2 in Solid Argon and Neon

Abstract: Laser-ablated palladium and platinum atoms react with NO in excess argon or neon to form Pd(NO)1,2 and Pt(NO)1,2 as major products. DFT calculations are found to be effective in reproducing experimental results and in assigning observed bands. Nitrosyl cation and anion species are observed with both metals, and a linear relationship is found between the charge and nitrosyl stretching frequencies in Pd(NO)+,0,- and Pt(NO)+,0,- that allows estimates of charges on supported Pt and Pd catalysts to be made.

Reactions of Iron Atoms with Nitric Oxide and Carbon Monoxide in Excess Argon: Infrared Spectra and Density Functional Calculations of Iron Carbonyl Nitrosyl Complexes†

Abstract: Laser-ablated iron atoms react with CO and NO during condensation in excess argon to produce a series of iron carbonyl nitrosyl complexes. The Fe(CO)(NO), Fe(CO)2(NO), Fe(CO)(NO)2, and Fe(CO)2(NO)2 complexes are formed as reaction products during sample deposition and further annealing, which leads to dominance for the saturated Fe(CO)2(NO)2 complex. The Fe(CO)(NO) complex isomerizes to Fe(CO)(η2-NO) on visible photolysis and to the isocyanate species OFeNCO on ultraviolet irradiation. The observed absorption bands were identified by isotopic substitution (13C16O, 15N16O, 15N18O, and mixtures) and reproduced by DFT calculations of vibrational fundamentals. The FeCO subunit observed here in different nitrosyl environments appears to distort and stiffen with an increase in positive charge on iron, which may relate to the deformability of the FeCO subunit in heme proteins. The nature of bonding and reaction mechanism are discussed.

A Study of the Products of the Reaction of Phosphorus and Dioxygen

Abstract: The products of the reaction of laser-ablated red phosphorus and dioxygen have been studied using experiment and theory. The bands at 480.3 and 1273.3 cm-l, previously attributed to PO3 in the matrix isolation IR experiments, are reassigned to PO3-. Also observed in experiment are PO2, PO2-, P2O, OPOPO, P4, and higher oxides.

Infrared spectra of the CS2−, CS2+, and C2S4+ molecular ions in solid neon and argon

Abstract: Laser ablation of transition metal targets with concurrent code position of CS2/Ne and CS2/Ar mixtures produces metal independent absorptions at 1206.8 and 1159.2 cm−1 in neon and 1200.5 and 1160.4 cm−1 in argon due to CS2+ and CS2−. Additional metal independent absorptions at 1385.2 cm−1 in neon and 1379.7 cm−1 in argon increase on annealing. Isotopic substitutions show that this vibration involves two equivalent CS2 subunits. Based on density functional theory calculations of structure and vibrational frequencies, the 1385.2 and 1379.7 cm−1 bands are assigned to the C2S4+ cation in solid neon and argon. Identical experiments using matrix samples doped with the electron trapping molecule CCl4 enhance the 1385.2 and 1379.7 cm−1 absorptions and further support the cation assignment. No evidence was found for the (CS2)2− anion in these experiments.

Characterization of the Reaction Products of Laser-Ablated Lanthanide Metal Atoms with Nitric Oxide. Infrared Spectra of the NLnO Molecules in Solid Argon†

Abstract: This paper reports stretching frequencies of the novel NLnO lanthanide nitride, oxide molecules and the NCeO- and NPrO- anions in solid argon. Combination bands observed for NCeO, NPrO, NNdO, and NTbO confirm these assignments, and density functional calculations are presented to model the vibrational potentials of NCeO, NPrO, NNdO, NGdO, NTbO, and NLuO. The Ln−O frequencies of the NLnO molecules range from 800 to 720 cm-1, except for the case of NEuO, which is lower, near the EuO diatomic molecule. The Ln−N frequencies of the NLnO molecule depend on the availability of electrons for the LnN bond after the LnO double bond has been satisfied and, therefore, suggest the presence of three different bond orders, depending on the metal center. In NLuO, the Lu−N mode is 425.6 cm-1, and the Lu atom retains a filled f-shell; the Ce−N bond of NCeO has a higher frequency, 690.8 cm-1, and NPrO has a Pr−N mode at 900.8 cm-1, which is even higher than the PrN diatomic mode (857.9 cm-1). In addition, NO complexes with ...

Matrix Infrared Spectra and Density Functional Calculations for GaNO, InNO, and TlNO

Abstract: Laser-ablated Ga, In, and Tl atoms react with NO during condensation in excess argon at 10 K to give one major product, which absorbs at 1578.5 cm-1 for Ga, 1524.9 cm-1 for In, and 1454.6 cm-1 for Tl. Infrared spectra of 14N16O, 15N16O, 15N18O, and mixed isotopic samples show that this product is the metal nitrosyl MNO. Density functional calculations provide good agreement for 3Σ- GaNO and InNO, but higher level MP2 calculations are required to explain the bent structure and decreased N−O frequency for 3A‘ ‘ TlNO. Model DFT calculations are also reported for Li[NO] and Li[NO]Li.

Reactions of Laser-Ablated Ruthenium Atoms with CO and H2 Mixtures: Infrared Spectra and Density Functional Theory Calculations of H2Ru(CO)x (x = 2−4) and (H2)RuCO

Abstract: Reactions of laser-ablated ruthenium atoms with carbon monoxide and hydrogen in solid argon produce the unsaturated ruthenium carbonyl dihydride H2Ru(CO)2 and the hydrogen complexes (H2)xRuCO (x = 1, 2). The observed absorption bands of the reaction products are identified by isotopic substitution and reproduced well by DFT calculations of vibrational fundamentals. The growth of bands due to H2Ru(CO)2 and (H2)RuCO during annealing in solid argon indicates that ruthenium monocarbonyl is coordinated with H2 to form the dihydrogen complex (H2)RuCO, while H2Ru(CO)2 is formed from the (H2)RuCO complex inserting into (H2) upon coordinating with another CO. Weak bands due to H2Ru(CO)3 and H2Ru(CO)4 are also observed.

Reactions of Laser-Ablated Boron Atoms with Methyl Halides in Excess Argon. Infrared Spectra and Density Functional Theory Calculations on CH3BX, CH2BX, and CHBX (X = F,Cl,Br)

Abstract: Laser-ablated boron atoms react with methyl fluoride in an argon stream to form two major products: CH2BF and CHBF. In similar reactions of boron with methyl chloride and methyl bromide, both CH2BX and CHBX are also observed, as well as the primary insertion products, CH3BCl and CH3BBr, respectively. Infrared spectra of isotopic combinations of B and CH3X and density functional theory frequency calculations provide evidence for the product identification. Both products form via insertion into the C−X bond followed by loss of one or two H atoms for all reactions. Comparisons are made with the products of the reactions of B with C2H6, CH3NH2, and CH3OH, all of which are isoelectronic with CH3F. The calculations not only predict the vibrational frequencies exceptionally well, but also predict that there is no dative bonding in either CH2BX or CHBX, despite the empty p-orbital on B and the filled p-orbitals on the halogen atom.

Reactions of Laser-Ablated Osmium and Ruthenium Atoms with Nitric Oxide in Neon and Argon. Matrix Infrared Spectra and Density Functional Calculations of Os(NO)1-3, Ru(NO)1-3, NOsO, NRuO, OsNO+ and RuNO+

Abstract: Laser-ablated osmium and ruthenium are reacted with nitric oxide and the products are isolated in solid neon and argon. The primary products in both neon and argon are the nitrosyl complexes M(NO)1-3. Sharp, weak bands due to the mononitrosyl cations are also observed. The insertion products NMO observed for both metals differ in their stability relative to MNO; NOsO is more stable than OsNO whereas the reverse is the case for RuNO and NRuO. Density functional theory (DFT) calculations effectively reproduce the experimental observations and predict frequencies of chemically useful accuracy. The calculated isotopic ratios are also in very good agreement with experiment, showing that DFT correctly describes the normal modes in these molecules.

Reactions of Laser-Ablated Rhodium and Iridium Atoms with Nitric Oxide in Neon and Argon. Matrix Infrared Spectra and Density Functional Calculations of Rh(NO)1-3, Ir(NO)1-3, NRhO, NIrO, RhNO+, and IrNO+

Abstract: Laser-ablated rhodium and iridium atoms are reacted with nitric oxide and the products are isolated in solid neon and argon. Neutral nitrosyl complexes Rh(NO)1-3 and Ir(NO)1-3 are the main products, and weaker bands due to RhNO+, IrNO+, NRhO, and NIrO are also observed. DFT calculations for these products using the BPW91 and B3LYP functionals determine frequencies with the same accuracy found for other metal nitrosyls and are a useful predictive tool. The stretching frequencies observed for the isolated nitrosyls are close to those for analogous nitrosyl species on rhodium and iridium surfaces, which will aid in interpreting vibrational data for surface species.