Showing papers by "Lester Andrews published in 2002"

Noble gas-actinide compounds: complexation of the CUO molecule by Ar, Kr, and Xe atoms in noble gas matrices.

Abstract: The CUO molecule, formed from the reaction of laser-ablated U atoms with CO in a noble gas, exhibits very different stretching frequencies in a solid argon matrix [804.3 and 852.5 wave numbers (cm−1)] than in a solid neon matrix (872.2 and 1047.3 cm−1). Related experiments in a matrix consisting of 1% argon in neon suggest that the argon atoms are interacting directly with the CUO molecule. Relativistic density functional calculations predict that CUO can bind directly to one argon atom (U-Ar = 3.16 angstroms; binding energy = 3.2 kilocalories per mole), accompanied by a change in the ground state from a singlet to a triplet. Our experimental and theoretical results also suggest that multiple argon atoms can bind to a single CUO molecule.

OCBBCO: A neutral molecule with some boron-boron triple bond character

Abstract: Molecules that contain boron−boron multiple bonds are extremely rare due to the electron-deficient nature of boron. Here we report experimental and theoretical evidence of a neutral OCBBCO molecule with some boron−boron triple bond character. The molecule was produced and unambiguously characterized by matrix isolation infrared spectroscopy. Quantum chemical calculations indicate that the molecule has a linear singlet ground state with a very short boron−boron bond length.

Infrared Spectra of the Novel Si2H2 and Si2H4 Species and the SiH1,2,3 Intermediates in Solid Neon, Argon, and Deuterium

Abstract: Laser-ablated silicon atoms react extensively with hydrogen to form the silicon hydrides SiH1,2,3,4 and the disilicon hydrides Si2H2,4,6. Infrared spectra and density functional theory frequency ca...

Noble gas-actinide compounds: Evidence for the formation of distinct CUO(Ar)(4-n)(Xe)(n) and CUO(Ar)(4-n)(Kr)(n) (n=1, 2, 3, 4) complexes

Abstract: Laser-ablated U atoms react with CO in excess argon to produce CUO, which gives rise to 852.5 and 804.3 cm-1 infrared absorptions for the triplet state CUO(Ar)n complex in solid argon at 7 K. Relativistic density functional calculations show that the CUO(Ar) complex is stable and that up to four or five argon atoms can complex to CUO. When 1−3% Xe is added to the argon/CO reagent mixture, strong absorptions appear at 848.0 and 801.3 cm-1 and dominate new four-band progressions, which increase on annealing to 35−50 K as Xe replaces Ar in the intimate coordination sphere. Analogous spectra are obtained with 1−2% Kr added. This work provides evidence for eight distinct CUO(Ng)n(Ar)4-n (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes and the first characterization of neutral complexes involving four noble-gas atoms on one metal center.

Matrix Infrared Spectra and DFT Calculations of the Reactive MHx (x = 1, 2, and 3), (H2)MH2, MH2+, and MH4- (M = Sc, Y, and La) Species

Abstract: Laser-ablated Sc, Y, and La react with molecular hydrogen to give MH, MH2+, MH2, MH3, and MH4- (M = Sc, Y, and La) during condensation in excess argon for characterization by matrix infrared spectroscopy. Annealing forms the dihydrogen complex (H2)MH2, which can be reduced to MH4- by electron capture. The (HD)MHD complex exchanges hydrogen positions on broadband photolysis to form primarily the (D2)MH2 complex. Doping the samples with CCl4 to capture ablated electrons markedly increases the MH2+ infrared band intensities and decreases the MH4- absorptions. Further annealing produces higher (H2)2MH2 complexes, which also exchange hydrogen positions. The reaction products are identified by deuterium and deuterium hydride isotopic substitution. DFT and MP2 theoretical calculations are employed to predict geometries and vibrational frequencies of these novel molecules, complexes, anions, and cations. Charged species from laser-ablation contribute more to the spectra of group 3 reaction products than for any o...

Infrared vibronic absorption spectrum and spin–orbit calculations of the upper spin–orbit component of the Au3 ground state

Abstract: Laser-ablated gold co-deposited with excess neon at 3.5 K produces a new sharp 2025.5-cm−1 absorption. Annealing to 8 K increases this absorption ten-fold and produces six weaker associated vibronic bands with 172- and 118-cm−1 intervals. Relativistic configurations (RCI) computations are carried out for several electronic states lying below 4.4 eV. These calculations show that the spin–orbit effect stabilizes the D3h structure and quenches Jahn–Teller distortion. They also predict a 0.2-eV spin–orbit splitting of the Au3 ground state, which is in excellent agreement with the 2025.5-cm−1 neon matrix band origin. We have also confirmed the assignment of the A-X system at 1.8 eV observed by Bishea and Morse. The observed vibronic intervals are in accord with calculated a1′ and e′ stretching fundamentals and they confirm the D3h geometry for Au3. This work reports the first observation of the ground-state spin–orbit splitting of a heavy metal trimer.

Infrared Spectra and Density Functional Theory Calculations of Group 6 Transition Metal Sulfides in Solid Argon

Abstract: Laser-ablated chromium, molybdenum, and tungsten atoms react with discharged sulfur vapor during cocondensation in excess argon. On the basis of the metal isotopic splittings, 34S isotopic substitution, and mixed 32S + 34S experiments, the primary reaction product MS2 molecules are identified. The S−M−S bond angles in the MS2 molecules are determined from isotopic frequencies as 115° ± 4°, 114° ± 3°, and 114° ± 8° for M = Cr, Mo, and W, respectively. Other reaction products, including CrS, CrS3, and WS3, are also characterized. DFT calculations using both B3LYP and BPW91 functionals produce consistent results for the Mo and W compounds and are in excellent agreement with experimental frequencies. For chromium sulfides, the BPW91 functional calculations give satisfactory results.

Infrared spectra of rhodium hydrides in solid argon, neon, and deuterium with supporting density functional calculations

Abstract: Laser-ablated Rh atoms react with H 2 to give RhH 2 and RhH as primary products, which are trapped or react with additional hydrogen in the condensing solid argon, neon, and deuterium matrixes RhH gives a major 19206 cm - 1 band in argon, a minor 19355 cm - 1 band in neon, and no absorption in deuterium RhH 2 produces sharp 20994 and 20534 cm - 1 and 20997 and 20522 cm - 1 bands in solid argon and neon, respectively and no absorption in deuterium; these absorptions increase on annealing the matrix to allow diffusion, which shows that ground state Rh inserts spontaneously into H 2 Additional absorptions at 21224 and 20782 cm - 1 (15273 and 14944 cm - 1 with D 2 ) in neon and at 15211 and 14961 cm - 1 in deuterium are assigned to the higher hydride complexes (H 2 )RhH 3 and (H 2 )RhH 2 , respectively A weaker 7376 cm - 1 absorption in neon is due to the side-bound complex Rh(H 2 ) 2 Both (D 2 )RhH 2 and Rh(H 2 )(D 2 ) rearrange H and D on photoexcitation suggesting a tetrahedral transition state Rhombic (RhH) 2 is observed in all three matrix systems These assignments are supported by D 2 , HD, and H 2 + D 2 substitution and density functional theory frequency and structure calculations

Experimental and Theoretical Studies of the Products of Laser-Ablated Thorium Atom Reactions with H2O in Excess Argon

Abstract: Reactions of laser-ablated Th atoms with H2O during condensation in excess argon have formed a variety of intriguing new Th, H, O species. Infrared absorptions at 1406.0 and 842.6 cm-1 are assigned to the H−Th and ThO stretching vibrations of HThO. Absorptions at 1397.2, 1352.4, and 822.8 cm-1 are assigned to symmetric H−Th−H, antisymmetric H−Th−H, and ThO stretching vibrations of the major primary reaction product H2ThO. Thorium monoxide (ThO) produced in the reaction inserts into H2O to form HThO(OH), which absorbs at 1341.0, 804.0, and 542.6 cm-1. Both HThO(OH) and ThO2 add another H2O molecule to give HTh(OH)3 and OTh(OH)2, respectively. Weaker thorium hydride (ThH1-4) absorptions were also observed. Relativistic DFT and ab initio calculations were performed on all proposed molecules and other possible isomers. The good agreement between experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts provides support for these first identifications of Th, H, O...

Infrared spectra and density functional theory calculations of group 8 transition metal sulfide molecules.

Abstract: Laser-ablated titanium, zirconium, and hafnium atoms react with discharged sulfur vapor during co-condensation in excess argon. The primary reaction product MS2 molecules are identified for the first time, and evidence for metal monosulfides is also presented. The ν1 and ν3 modes for TiS2, ZrS2, and HfS2 absorb at 533.5 and 577.8 cm-1, 502.9 and 504.6 cm-1, and 492.2 and 483.2 cm-1, respectively, in solid argon. On the basis of the isotopic frequencies for the ν3 modes, the bond angles of TiS2, ZrS2, and HfS2 are determined as 113 ± 4°, 107 ± 4°, and 108 ± 4°. DFT/B3LYP calculations predict 1A1 ground states and bond angles of 113.3°, 108.5°, and 109.5°, for the MS2 molecules, M = Ti, Zr, and Hf, respectively, and frequencies in excellent agreement with the observed values. The same calculation also predicts 3Δ ground states for TiS and ZrS, the 1Σ+ ground state for HfS, and frequencies in agreement with the observed values.

Neon Matrix Infrared Spectrum of WH6: A Distorted Trigonal Prism Structure

Abstract: Reactions of laser-ablated W atoms and H2 molecules during condensation in excess neon give the WH, WH2, WH3, WH4, and WH6 hydride products. WH6 absorptions increase on annealing to allow diffusion and further reaction of H2 and decrease on photolysis such that six infrared bands can be grouped and assigned to WH6. Excellent agreement between four observed neon matrix and four DFT calculated W−H stretching modes (two a1 and two e) and bending and deformation modes (a1 and e) confirms the present neon matrix preparation of WH6 and the previous theoretical predictions of a distorted trigonal prism structure which is far from octahedral.

Neon Matrix Infrared Spectra and DFT Calculations of Tungsten Hydrides WHx (x = 1−4, 6)

Abstract: Laser-ablated tungsten atoms react with molecular hydrogen upon condensation in excess neon. The tungsten hydrides WH, WH2, WH3, WH4, and WH6 are identified by isotopic substitution (D2, HD) and by density functional theory calculations of vibrational fundamentals. The WH diatomic gives a 1860.2 cm-1 band, WH2 gives a strong 1831.9 cm-1 absorption, and WH3 gives a sharp 1894.6 cm-1 peak. Absorptions due to WH4 appear at 1920.1 and 525.2 cm-1, increase on annealing in solid neon, and support a tetrahedral structure. Sharp new absorptions at 2021.2, 2004.4, 1953.8, 1927.5, 1080.3, and 840.7 cm-1 are assigned to WH6, based on deuterium isotopic shifts and comparison with frequencies computed by DFT for the distorted trigonal prism structure predicted earlier to be the global minimum energy structure for WH6. The bands of WH6 increase on annealing, decrease on broadband photolysis, and restore on further annealing. This is the first experimental identification of the WH2, WH4, and WH6 hydride molecules, and W...

Experimental and theoretical infrared spectra of Co2CO

Abstract: Matrix infrared spectra of Co2CO were obtained from cobalt vapors condensed with different isotopically substituted mixtures of carbon monoxide diluted in argon at 10 K. New bands at 1953.3, 488.7, 357.9, and 270.9 cm−1 are assigned to the νC–O, νM–CO, νM–C–O, and νM–M fundamentals, respectively. Computations performed using density functional theory with the generalized gradient approximation (DFT-GGA) for the exchange-correlation potential predict the lowest energy state of Co2CO to be 5A″ with the angle Co–Co–C of 116°. Our DFT-GGA vibrational frequencies of this state agree with the experimental frequencies extremely well—within 15 cm−1. Our estimate for the Co2–CO bond strength is 1.60 eV. Computed vibrational frequencies for Co2CO+ and Co2CO− are included for comparison.

Infrared Spectra and DFT Calculations for the Gold Hydrides AuH, (H2)AuH, and the AuH3 Transition State Stabilized in (H2)AuH3

Abstract: Reactions of laser-ablated gold atoms with hydrogen (H2, D2, HD) in excess argon and neon and in pure deuterium produced AuH and the (H2)AuH and (H2)AuH3 complexes in increasing yields, respectively, in these matrix hosts. The diatomic molecule AuH absorbs at 2226.6 cm-1 in solid argon, slightly blue shifted from the gas-phase value, and the stable (H2)AuH complex appears at 2173.6 cm-1 on annealing to allow diffusion and association of H2 and AuH. The higher (H2)AuH3 complex presents at 1642.0 cm-1 on deposition. In neon (H2)AuH and (H2)AuH3 give weak bands at 2170 and 1684 cm-1 with D2 counterparts at 1559 and 1207 cm-1, which become strong 1556.5 and 1198.6 cm-1 absorptions in pure deuterium. DFT structure and frequency calculations confirm these assignments and show that the AuH3 transition state with an imaginary b1 bending frequency is stabilized in the (H2)AuH3 complex with a real b1 bending frequency observed at 457.0 cm-1 for (D2)AuD3.

Reactions of Laser-Ablated Gold with Nitric Oxide: Infrared Spectra and DFT Calculations of AuNO and Au(NO)2 in Solid Argon and Neon†

Abstract: Laser-ablated gold reacts with nitric oxide in excess argon and neon, yielding the neutral nitrosyl complexes AuNO and Au(NO)2 as the main products. The N−O and Au−N stretching modes of AuNO are observed at 1701.9 and 517.6 cm-1 in solid argon and at 1710.4 and 523.8 cm-1 in solid neon. Both BPW91 and B3LYP density functionals predict 1A‘ state frequencies in very good agreement. An NBO analysis suggests more d orbital involvement in the bonding in AuNO than in the copper and silver nitrosyls. The dinitrosyl Au(NO)2 is observed at 1510.7 and 3183.2 cm-1 in solid argon and at 1528.2 and 3204.1 cm-1 in solid neon, which are in good agreement with DFT quartet state fundamental and combination frequencies: Au(NO)2 shows evidence for increased charge transfer and sd hybridization compared to AuNO. The cation nitrosyls Au(NO)1,2+ are minor products.

Matrix Infrared Spectra and Quasirelativistic DFT Studies of ThS and ThS2

Abstract: Laser-ablated thorium atoms react with discharged sulfur vapor during co-condensation in excess argon at 7 K. The ThS fundamental is observed at 474.7 cm-1, and the ν1 and ν3 modes for ThS2 are observed at 451.4 and 431.5 cm-1, respectively, based on sulfur-34 substitution and infrared spectra of sulfur 32, 34 mixtures. Sulfur isotopic ν3 vibrational frequencies for ThS2 indicate a 112 ± 5° upper limit for the S−Th−S bond angle. Quasirelativistic DFT calculations performed on ThS and ThS2 find that ThS has the 1Σ+ ground state, and ThS2 has the 1A1 ground state with a bond angle of 111.6°. Calculated vibrational frequencies are in excellent agreement with the observed values, and support this first identification of molecular thorium sulfides.

Reactions of Laser-Ablated Rhenium Atoms with Carbon Dioxide: Matrix Infrared Spectra and Density Functional Calculations on OReCO, O2ReCO, ORe(CO)2, O2Re(CO)2, OReCO-, and ORe(CO)2-

Abstract: Laser-ablated rhenium atoms react with CO2 molecules upon co-condensation in excess argon at 7 K and neon at 4 K. Besides neutral products [OReCO, O2ReCO, ORe(CO)2, and O2Re(CO)2], anionic species [OReCO-, ORe(CO)2-] are formed and identified through annealing, ultraviolet irradiation, isotopic substitution, and CCl4 doping experiments. DFT calculations have been performed on all product species, and the very good overall agreement between the calculated and the observed vibrational frequencies supports the product identifications.

Reactions of Laser-Ablated Osmium and Ruthenium Atoms with Carbon Dioxide: Matrix Infrared Spectra and Density Functional Calculations on OMCO, O2MCO, OMCO- (M = Os, Ru), O2Os(CO)2, and OCRu(O2)CO

Abstract: Laser-ablated Os and Ru atoms react with CO2 molecules upon cocondensation in excess argon at 7 K and neon at 4 K. Besides the dominant neutral products [OMCO, O2MCO (M = Os, Ru), O2Os(CO)2, and OCRu(O2)CO], anionic species [OMCO- (M = Os, Ru)] are also formed and identified through annealing, ultraviolet irradiation, isotopic substitution, and CCl4-doping experiments. DFT calculations have been performed on possible products, and the overall agreement between the calculated and observed vibrational absorptions supports the product identifications.

Infrared Spectrum of the Novel Electron-Deficient BH4 Radical in Solid Neon

Abstract: Laser-ablated boron reacts with hydrogen on condensation in excess neon to give BH4 radical, BH4- anion, and B2H6 as the major products. Identifications are based on 10B and D substitution, DFT frequency calculations, and comparison to previous spectra. Infrared spectra of BH4 support the C2v structure deduced from previous ESR spectra and theoretical calculations with two normal B-H bonds and two long B-H bonds for this novel electron-deficient radical. NBO analysis suggests that the two long B-H bonds and the H- -H bond are one-electron bonds.

Rhodium Dinitrogen Complexes Rh(NN)x (x = 1−3) and Anions: Matrix Infrared Spectra and DFT Calculations

Abstract: Reactions of laser-ablated rhodium atoms with molecular nitrogen in excess neon produce the rhodium nitrogen complexes Rh(NN)x (x = 1−3) and their counterpart anions through the capture of ablated electrons. The observed absorption bands are identified by isotopic substitution and DFT calculations of vibrational fundamentals. The N−N stretching fundamental at 2162.0 cm-1 for RhNN and the antisymmetric N−N mode for Rh(NN)2 at 2199.3 cm-1 in solid neon are in accord with earlier argon matrix assignments. Three N−N stretching frequencies at 2185.2, 2203.3, and 2235.6 cm-1 are assigned to Rh(NN)3, which is calculated to have a T-shaped structure with a 2A1 ground state. The photosensitive Rh(NN)x- (x = 1−3) anions are eliminated with CCl4 doping to capture ablated electrons.

Infrared Spectra and Density Functional Calculations for Early First-Row Transition Metal Nitrosyls in Solid Neon

Abstract: Reactions of laser-ablated Sc, Ti, V, Cr, and Mn with NO in excess neon give the same major products found in excess argon with several interesting differences. The argon-to-neon matrix shifts range from +43 cm-1 for the small Sc[NO]+ cation to −5 cm-1 for Sc[NO]. The lower polarizability of neon leads to a slower condensation rate and allows more reagent diffusion and reaction under the conditions of these experiments, and as a result, higher nitrosyls are observed on condensation in excess neon. Another consequence of the slower condensation rate of neon is the inability to trap as much of the side-bound M[NO] precursor relative to the NMO insertion product: higher yields of M[NO] species are trapped in solid argon. An advantage of the greater inertness of neon is its ability to trap cations with less perturbation than argon. Model calculations show that argon interacts more strongly with Sc[NO]+ than with neon: the ArSc[NO]+ species is stable and has a lower N−O stretching frequency than NeSc[NO]+. N...