CUO Molecule Research Articles

A light weight regularization for wave function parameter gradients in quantum Monte Carlo

The parameter derivative of the expectation value of the energy, ∂E/∂p, is a key ingredient in variational Monte Carlo (VMC) wave function optimization methods. In some cases, a naïve estimate of this derivative suffers from an infinite variance, which inhibits the efficiency of optimization methods that rely on a stable estimate of the derivative. In this work, we derive a simple regularization of the naïve estimator, which is trivial to implement in existing VMC codes, has finite variance, and a negligible bias, which can be extrapolated to zero bias with no extra cost. We use this estimator to construct an unbiased, finite variance estimation of ∂E/∂p for a multi-Slater–Jastrow trial wave function on the LiH molecule and in the optimization of a multi-Slater–Jastrow trial wave function on the CuO molecule. This regularized estimator is a simple and efficient estimator of ∂E/∂p for VMC optimization techniques.

Electronic transition and cascading decay of CuO molecule in the wavelength region 430–550 nm investigated by laser-induced fluorescence spectroscopy

The electronic spectrum of the copper monoxide molecule (CuO) was investigated in the range of 430–550 nm using laser induced fluorescence spectroscopy and single vibronic level emission spectra. The CuO molecule was produced by a supersonic jet-cooled discharge assisted laser ablation of Cu target. Twenty two vibronic bands were observed and assigned to the electronic transition progressions from the ground state X2Пi to excited states C2П3/2, C2П1/2, D2Δ5/2, E2Δ5/2, F2П3/2, G2Σ−, H2П3/2, and I2П3/2, of which ten bands were recorded firstly. The molecular constants of the excited electronic states for 63CuO and 65CuO isotopologues were obtained by a rotational analysis of the spectra. Cascading processes in the electronic excited states were found combining the time-resolved single vibronic level emission spectroscopy. The time-dependent radiative decay curves corresponding to different decay processes were recorded and analyzed.

Unravelling the quantum-entanglement effect of noble gas coordination on the spin ground state of CUO

The accurate description of the complexation of the CUO molecule by Ne and Ar noble gas matrices represents a challenging task for present-day quantum chemistry. Especially, the accurate prediction of the spin ground state of different CUO--noble-gas complexes remains elusive. In this work, the interaction of the CUO unit with the surrounding noble gas matrices is investigated in terms of complexation energies and dissected into its molecular orbital quantum entanglement patterns. Our analysis elucidates the anticipated singlet--triplet ground-state reversal of the CUO molecule diluted in different noble gas matrices and demonstrates that the strongest uranium-noble gas interaction is found for CUOAr4 in its triplet configuration.

The electronic spectrum of CUONg4 (Ng = Ne, Ar, Kr, Xe): New insights in the interaction of the CUO molecule with noble gas matrices

The electronic spectrum of the CUO molecule was investigated with the IHFSCC-SD (intermediate Hamiltonian Fock-space coupled cluster with singles and doubles) method and with TD-DFT (time-dependent density functional theory) employing the PBE and PBE0 exchange-correlation functionals. The importance of both spin-orbit coupling and correlation effects on the low-lying excited-states of this molecule are analyzed and discussed. Noble gas matrix effects on the energy ordering and vibrational frequencies of the lowest electronic states of the CUO molecule were investigated with density functional theory (DFT) and TD-DFT in a supermolecular as well as a frozen density embedding (FDE) subsystem approach. This data is used to test the suitability of the FDE approach to model the influence of different matrices on the vertical electronic transitions of this molecule. The most suitable potential was chosen to perform relativistic wave function theory in density functional theory calculations to study the vertical electronic spectra of the CUO and CUONg(4) with the IHFSCC-SD method.

Configuration interaction studies on the electronic states of the CUO molecule

Relativistic multireference configuration interaction calculations are carried out on the low-lying electronic states of the CUO molecule at linear geometries. The results of these and previous CUO calculations are discussed on the basis of the natures of these states and the advantages and disadvantages of different methods of computing electronic structure. We find the state, at its minimum geometry, to be 0.17 eV lower then the 3Φ2 state at its minimum energy geometry. The principal term of the state is 82.1% of the wave function with no large secondary terms. The principal term of the 3Φ2 state is 70.8% of the wave function with a secondary 3Δ2 term being 11.6% of the wave function. Calculations on CUO(Ar) at previously optimised geometries give the lowest state as 1 A′.

The importance of spin-orbit coupling and electron correlation in the rationalization of the ground state of the CUO molecule.

We present calculations at the relativistic coupled cluster theory that predict the (1)Sigma(0) (+) ground state of CUO to lie 58.2 kJ/mol below the first excited state, (3)Phi(2). This can be contrasted with the outcome of earlier density functional theory and complete active space second order perturbation theory (CASPT2) calculations that both predicted a (3)Phi(2) ground state upon inclusion of spin-orbit coupling in the calculations. Our result gives further justification to the interpretation of the measured frequency shifts of this species in various noble gas matrices as being caused by significant interaction between the uranium and the heavier noble gas atoms.

Properties of Low-k Cu Barrier SiOCNH Film Deposited by Plasma-Enhanced Chemical Vapor Deposition using Hexamethyldisiloxane and Ammonia Gases

We developed SiOCNH films that act as a barrier to copper (Cu) thermal diffusion by plasma-enhanced chemical vapor deposition (PE-CVD) using hexamethyldisiloxane (HMDSO) and ammonia (NH3) gases. The k value is in the range of 3.87 to 5.48, which is lower than that of PE-CVD silicon nitride (SiN) and slightly larger than that of PE-CVD SiOCH. The leakage current is on the order of 10-9 to 10-10 A/cm2 at 1 MV/cm2, as low as the value of PE-CVD SiN film. The film can prevent Cu thermal diffusion at 450°C for 4 h in N2 ambient. The Cu thermal diffusion depth is less than 10 nm at a NH3 flow rate larger than 50 cc/min. The barrier ability of the SiOCNH film deposited using HMDSO and NH3 gases against Cu thermal diffusion is due to the average pore size being smaller than 0.52 nm, which is slightly larger than that of a CuO molecule, and the film density being larger than 1.83 g/cm3.

On the noble-gas-induced intersystem crossing for the CUO molecule: experimental and theoretical investigations of CUO(Ng)n (Ng = Ar, Kr, Xe; n = 1, 2, 3, 4) complexes in solid neon.

Uranium atoms excited by laser ablation react with CO in excess neon to produce the novel CUO molecule, which forms distinct Ng complexes (Ng = Ar, Kr, Xe) when the heavier noble gases are added. The CUO(Ng) complexes are identified through CO isotopic and Ng substitution on the neon matrix infrared spectra and by comparison to DFT frequency calculations. The U-C and U-O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from frequencies for the (1)Sigma(+) CUO ground state, which identifies singlet ground state CUO(Ng) complexes. In solid neon the CUO molecule is also a complex CUO(Ne)(n), and the CUO(Ne)(n-1)(Ng) complexes are likewise specified. The next singlet CUO(Ne)(x)(Ng)(2) complexes in excess neon follow in like manner. However, the higher CUO(Ne)(x)(Ng)(n) complex (n = 3, 4) stretching modes approach pure argon matrix CUO(Ar)(n) values and isotopic behavior, which are characterized as triplet ground state complexes by DFT frequency calculations. This work suggests that the singlet-triplet crossing occurs with 3 Ar, 3 Kr, or 4 Xe and a balance of Ne atoms coordinated to CUO in the neon matrix host.

Noble gas–uranium coordination and intersystem crossing for the CUO(Ne)x(Ng)n(Ng = Ar, Kr, Xe) complexes in solid neon

Atomic uranium excited by laser ablation reacts with CO in excess neon to produce the novel CUO molecule, which forms weak complexes CUO(Ne)m with neon and stronger complexes CUO(Ne)x(Ng)n (Ng = Ar, Kr, Xe) when the heavier noble gas atoms are present. The heavier CUO(Ne)m − 1(Ng) complexes are identified through the effects of CO isotopic and Ng substitution on the neon matrix infrared spectra and by comparison to DFT frequency calculations on the model complexes CUO(Ng) (Ng = Ne, Ar, Kr, Xe). The U–C and U–O stretching frequencies of CUO(Ne)m − 1(Ng) complexes are slightly red shifted from the 1047 and 872 cm−1 frequencies for the 1Σ+ CUO ground state neon complex, which identifies singlet ground state CUO(Ne)m − 1(Ng) complexes in solid neon. The next singlet CUO(Ne)x(Ng)2 complexes in excess neon follow in like manner. However, stretching modes and the isotopic shifts of the higher CUO(Ne)x(Ng)n complexes approach those of the pure argon matrix CUO(Ar)n complex, which characterizes triplet ground state complexes by comparison to DFT frequency calculations.

Bonding of multiple noble-gas atoms to CUO in solid neon: CUO(Ng)n (Ng=Ar, Kr, Xe; n=1, 2, 3, 4) complexes and the singlet-triplet crossover point.

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.

Noble gas-actinide complexes of the CUO molecule with multiple Ar, Kr, and Xe atoms in noble-gas matrices.

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 ((12)C(16)O, (13)C(16)O, (12)C(18)O). 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 noble gas atoms bonded to one metal center.

The ground state and electronic spectrum of CUO: a mystery.

Results are presented from a theoretical study of the lower electronic states of the CUO molecule. Multiconfigurational wave functions have been used with dynamic correlation added using second order perturbation theory. Extended basis sets have been used, which for uranium were contracted including scalar relativistic effects. Spin orbit interaction has been included using the state-interaction approach. The results predict that the ground state of linear CUO is phi2 with the closed shell sigma(+)0 state 0.5 eV higher in energy. This is in agreement with matrix isolation spectroscopy, which predicts phi2 as the ground state when the matrix contains noble gas atoms heavier than Ne. In an Ne matrix, the experiments indicate, however, that CUO is in the sigma(+)0 state. The change of ground state due to the change of the matrix surrounding CUO cannot be explained by the results obtained in this work and remains a mystery.

Investigation of the A2$\Sigma$- state of CuO by laser-induced fluorescence

The laser-induced fluorescence excitation spectrum of the A2Σ--X2Π3/2 transition of CuO in the 540-620nm region has been studied, where the CuO molecule was produced by using the technique of dc discharge reaction under a supersonic condition. We have recorded and rotationally analysed the 0-0, 1-0, 2-0 and 3-0 bands. The rotational constants of the upper state A2Σ- were determined and vibrational constants improved. In addition, the lifetime measurement for the A2Σ- state was carried out under the collision-free condition and the lifetimes obtained are 469±2, 456±2, 488±3 and 490±4ns for v'=0, v'=1, v'=2 and v'=3 levels, respectively.

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

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.

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

A 3Φ state is found for the CUO molecule (made by reaction of laser-ablated U and CO) trapped in solid argon, in contrast to the 1Σ+ ground state in solid neon. The new electronic state results from the transfer of an electron from a U−C bonding orbital to a nonbonding 5f orbital of the U atom, thus decreasing the U−C stretching frequency significantly. Infrared spectroscopy and relativistic DFT calculations have been used to characterize these two low-lying states of CUO.

Reaction of Laser-Ablated Uranium Atoms with CO: Infrared Spectra of the CUO, CUO-, OUCCO, (η2-C2)UO2, and U(CO)x (x = 1−6) Molecules in Solid Neon

Laser-ablated uranium atoms have been reacted with CO molecules during condensation with neon at 4 K. Absorptions at 1047.3 and 872.2 cm-1 are assigned to the CUO molecule formed from the insertion reaction that requires activation energy. Isotopic substitution shows that the upper band is largely U−C and the lower band mostly U−O in vibrational character. Absorptions at 2051.5, 1361.8, and 841.0 cm-1 are assigned to the OUCCO molecule, which is formed by the CO addition reaction to CUO and ultraviolet−visible photon-induced rearrangment of the U(CO)2 molecule. The OUCCO molecule undergoes further photochemical rearrangment to the (C2)UO2 molecule, which is characterized by symmetric and antisymmetric OUO stretching vibrations at 843.2 and 922.1 cm-1. The uranium carbonyls U(CO)x (x = 1−6) are produced on deposition or on annealing. Evidence is also presented for the CUO- anion and U(CO)x- (x = 1−5) anions, which are formed by electron capture. Relativistic density functional theoretical calculations have been performed for the aforementioned species, which lend strong support to the experimental assignments of the infrared spectra. It is predicted that CUO is a linear singlet molecule with the shortest U−C bond yet characterized, and it has a U−C triple bond with substantial U 5f character. The theoretical analysis also finds that a distorted tetrahedral geometry of (C2)UO2 lies much lower in energy than either the bent/linear OUCCO structures or the U(CO)2 uranium dicarbonyl.

A chemical effect on light emission from ion-bombarded copper and aluminum surfaces

Spectra of visible and near UV light emitted from Cu and Al surfaces bombarded by 10 keV Kr + ions, and the influence of reactive gases present during bombardment have been measured. From the clean surfaces of the two metals, atomic emission lines of the neutral sputtered metal atoms are observed. For Cu, the presence of O 2 gas intensifies the atomic emission lines slightly and causes the appearance of features in the spectrum which can be correlated with emission from the CuO molecule. For Al, O 2 causes a large intensification of the atomic lines and the appearance of AlO emission. The presence of H 2O causes a further increase in the Al atomic emission plus the appearance of AlH and H atom emission. The magnitude of the intensification differs for different excited levels in the atoms. These effects are associated with the formation of a chemisorbed layer on the metal surface.