CO Vibrational Frequency Research Articles

Adsorption and activation of CO coadsorbed with K on Fe(100) surface: A plane-wave DFT study

The adsorption and diffusion properties of K atoms together with the coadsorption effects induced upon CO activation on Fe(100) surface have been studied using spin-polarized plane-wave density functional theory (DFT) calculations and the generalized gradient approximation. Preferential adsorption of K atoms takes place at surface hollow sites and diffusion among these sites has a small activation energy of only 0.7 kcal/mol. Substitutional adsorption of K at a surface Fe site is also possible but only at high temperatures required to overcome a barrier of about 36.0 kcal/mol. A systematic analysis of the modifications of binding properties for molecular (CO) and atomic (C,O) species upon interaction with K has been performed both as function of the relative separations as well as coverage using a series of (4 × 4), (3 × 3) and (2 × 2) supercell models. The presence of K leads to stabilization of both C and O species but in the last case significant variations were observed only when O is bonded at a bridge site. For CO molecule a relatively large range of stabilization energies can be induced by coadsorbed K depending on the relative CO–K separation and K coverage. The largest stabilization effects are observed at small separations, when K is located at a hollow site adjacent to CO binding site. In such cases the increase in binding takes place with important red shifts of CO vibrational frequency and with relatively large bond elongations, independent of CO binding mode on the surface. Relative to the bare surface, the presence of K was also found to reduce CO activation energies by as much as 6.2–7.8 kcal/mol, i.e. 25–31%, function of the relative separation and molecular coverage. Such effects have been correlated with the charge transfer from K to Fe surface and to CO molecule leading to an increased stabilization primarily of O and somewhat less of C species in the transition state and to reduction of the bond competition between CO and the surface atoms.

Adsorption of carbon monoxide on Pd low‐index surfaces and (110) reconstructed surface

AbstractAdsorption and diffusion of carbon monoxide on Pd low‐index surfaces and missing‐row Pd (110) reconstructed surface have been investigated by the extended London–Eyring–Polyani–Sato (LEPS) method constructed by means of a five‐parameter Morse potential. All critical characteristics, such as adsorption site, adsorption geometry, binding energy, CO vibrational frequency have been obtained and compared with the experimental and theoretical data. On these surfaces, the stable adsorption sites of CO are changed with increasing CO coverage. On the missing‐row Pd (110) reconstructed surface, there are five stable adsorption sites: H1, H2 (H1 and H2 are threefold hollow sites on (111) subsurface), B (bridge site on the second layer), SB (short‐bridge site), and T (top site). Copyright © 2010 John Wiley & Sons, Ltd.

CO and NO Adsorption and Dissociation at the Β-Mo2C(0001) Surface: A Density Functional Theory Study

Adsorption and dissociation of CO and NO molecules at the Mo- and C-terminated β-Mo2C(0001) surfaces has been investigated systematically using density functional theory methods together with cluster models. The calculations yield stable CO and NO adsorption for both surface terminations, suggesting strong adsorbate binding. Molecular adsorption of CO exhibits similar stability for the two terminations, while the molecular NO adsorbate prefers Mo termination over C termination. Computed vibrational frequencies of CO and NO are compared with data from infrared (IR) spectroscopy, allowing a detailed interpretation and assignment of the different features in the experimental spectra. C, N, and O atoms are quite strongly bound at the β-Mo2C surface, where at the Mo-terminated surface, hollow sites are energetically preferred. For the C termination, only oxygen adsorbs near carbon sites, whereas C and N stabilize above Mo substrate atoms or in hollow sites. Dissociative adsorption of NO is energetically prefer...

Crystalline 1H‐1,2,3‐Triazol‐5‐ylidenes: New Stable Mesoionic Carbenes (MICs)

Crystalline 1<i>H</i>‐1,2,3‐Triazol‐5‐ylidenes: New Stable Mesoionic Carbenes (MICs)

Interaction of CO Molecule with Au/MOR Catalyst: ONIOM-PM6 Study, Active Sites, Thermodynamic and Vibrational Frequencies

ONIOM calculations have been carried out to determine geometries, adsorption energies, and vibrational frequencies of CO on a model for Au-exchanged mordenite catalysts, Au/MOR. The CO-calculated vibrational frequencies (upsilon(CO)) are in good agreement with the reported experimental values. We proposed to interpret the frequency results. CH(3)COCH(3) and CH(3)SH adsorption enthalpy calculations on Au/MOR model show that the Au/MOR catalyst behaves like a soft acid according to Pearson's rule. A higher structural deformation degree of the mordenite was found in the calculations with PM6 than with universal force field approach approach. A new pseudopotential (ACEP-121) was developed to improve the Au-Au distance, and Au ionization potential.

Effect of Methanol on the Lewis Acidity of Rutile TiO2Nanoparticles Probed through Vibrational Spectroscopy of Coadsorbed CO

Infrared spectroscopy of adsorbed CO has been used to characterize the effect of adsorbed methanol on the Lewis acidity of 4 nm rutile TiO(2) nanoparticles. Measurements of CO absorbance and vibrational frequency have revealed that CO adsorbs primarily at one class of Lewis acid sites on clean TiO(2) particles, where evidence for lateral interactions between neighboring molecules suggests dense coverage occurs near saturation. The response of the CO infrared intensities and frequencies to methanol exposure has shown that methanol uptake occurs primarily at the Lewis acid sites and through hydrogen bonding to surface OH groups. These surface sites appear to be responsible for driving both molecular and dissociative adsorption of methanol on the titania. Most importantly, these studies have revealed that the parent methanol and associated methoxy products lower the Lewis acidity of neighboring sites on TiO(2) nanoparticles.

Adsorption of CO on gas phase and zeolite supported gold monomers: A computational study

We report for the first time the interaction of carbon monoxide with gold monomer in three oxidation states 0, +1 and +3 on FAU zeolite support using density functional theory. The gas phase structures of the gold carbonyls are retained on the zeolite support with only a slight change in the O–C–Au bond angle. For the supported cluster the CO vibrational frequency shows a blue shift on going to higher oxidation states. The CO binding energies on the supported gold monomers are 1.01, 1.15 and 1.12 eV in the oxidation states 0, +1 and +3, respectively.

Rotational study of carbon monoxide isotopologues in small 4He clusters

High resolution microwave (a-type) and millimetre-wave (b-type) spectra of He(N)-(13)C(16)O, He(N)-(12)C(18)O, and He(N)-(13)C(18)O clusters (N<or= 10) were observed, significantly extending the initial spectroscopic observations on He(N)-(12)C(16)O by Surin et al. [Phys. Rev. Lett., 2008, 101, 233401]. The frequencies of the a-type series, which evolves from the end-over-end rotation of the dimer, decrease from N = 1 to 3, then increase smoothly to at least N = 9. This turnaround indicates a rapid evolution of the solvation character from classical to quantum. The b-type series, which evolves from the free molecule rotation of CO, increases from N = 0 to 6 and then decreases to at least N = 10. This is consistent with an initially increasing anisotropy of the helium environment, followed by a tendency of the solvation shell to become more isotropic. The shift of the vibrational frequency of CO as determined from the infrared [A. R. W. McKellar, J. Chem. Phys., 2004, 121, 6868; ibid., 2006, 125, 164328] and microwave data reveals an approximately linear decrease from N = 1 to at least 9. If the linear shift were to continue until completion of the first solvation shell (N approximately 14), the estimated helium nanodroplet shift will be well undershot [K. von Haeften, S. Rudolph, I. Simanovski, M. Havenith, R. E. Zillich and K. B. Whaley, Phys. Rev. B: Condens. Matter Mater. Phys., 2006, 73, 054502]. In this case, there must be an upturn in the vibrational shift beyond N = 14, which is not predicted by theory [T. Skrbić, S. Moroni and S. Baroni, J. Phys. Chem. A, 2007, 111, 7640]. By extrapolating the a-type series to N = 14 (assuming a linear vibrational shift), we estimate the rotational constant, B, of CO in the helium nanodroplet to be approximately 74% of its gas phase value. This is in reasonable agreement with simulations (76% at N = 14), which predict the limiting value to be approximately reached upon completion of the first solvation shell (73% at N = 100) [T. Skrbić, S. Moroni and S. Baroni, J. Phys. Chem. A, 2007, 111, 7640]. However, this value is significantly larger than that inferred from helium nanodroplet experiments (63%).

Density-functional study of the CO adsorption on the ferromagnetic fcc Co(001) film surface

Experimental results on CO adsorption at the thin fcc Co(0 0 1) films have been obtained recently [L. Tskipuri, R.A. Bartynski, Surf. Sci. 603 (2009) 802] whereas theoretical analysis of this system is not available. In the present paper, we consider regular p ( 2 × 2 ) and c ( 2 × 2 ) CO overlayers adsorbed in the atop, bridge or hollow sites above the five-layer ferromagnetic fcc Co(0 0 1) film deposited at the Cu(0 0 1) surface. By using first-principles density-functional calculations with the correlation-exchange functional in the PBE form, we calculate the CO relaxed geometries, adsorption energies, stretching CO vibrational frequencies, work function and local magnetic moments on and near CO. We consider also an empirical adsorption-energy correction that might reduce the well-known flaw of many density-functional forms when applied to CO. We show also that in this correction, instead of the previously used stretching vibration frequency also the C–O distance can be used. The calculations suggest that the stable chemisorption site for the CO coverage θ = 0.25 or 0.50 is the atop position. Together with the calculated CO stretching vibrational frequencies this conclusion compares well with the experimental findings. The CO molecule acquires very small magnetic moment that couples antiferromagnetically to moments of cobalt atoms. The magnetization at Co atoms close to CO is slightly lowered, the effect being strongest for the atop adsorption. The overall picture is similar to that for the Co(0 0 0 1) and Co(1 1 1) surfaces.

Binding and docking interactions of NO, CO and O₂in heme proteins as probed by density functional theory.

Dynamics and reactivity in heme proteins include direct and indirect interactions of the ligands/substrates like CO, NO and O2 with the environment. Direct electrostatic interactions result from amino acid side chains in the inner cavities and/or metal coordination in the active site, whereas indirect interactions result by ligands in the same coordination sphere. Interactions play a crucial role in stabilizing transition states in catalysis or altering ligation chemistry. We have probed, by Density Functional Theory (DFT), the perturbation degree in the stretching vibrational frequencies of CO, NO and O2 molecules in the presence of electrostatic interactions or hydrogen bonds, under conditions simulating the inner cavities. Moreover, we have studied the vibrational characteristics of the heme bound form of the CO and NO ligands by altering the chemistry of the proximal to the heme ligand. CO, NO and O2 molecules are highly polarizable exerting vibrational shifts up to 80, 200 and 120 cm−1, respectively, compared to the non-interacting ligand. The importance of Density Functional Theory (DFT) methodology in the investigation of the heme-ligand-protein interactions is also addressed.

A DFT study of carbon monoxide adsorption on a Si4 nano-cluster

Using the gradient-corrected hybrid density functional method of Predew, Burke, and Ernzerhof (PBEPBE) and the new hybrid meta-density functional method of Truhlar (MPW1B95), the geometry, adsorption energy, vibrational frequency, and charge distribution of carbon monoxide adsorption on a Si4 nano-cluster has been studied. Taking into account spin multicipility in the calculations, a new stable structure of CO absorbed on the Si4 cluster has been found, in addition to the previously reported structures. Exhaustive vibrational frequency analysis of optimized structures shows that some of the formerly reported structures have imaginary vibrational frequencies and are not proper stable structures. Thus, they do not represent real local energy minima. Also, CO vibrational frequency analysis shows that a significant change of vibrational frequency in the stable structures occurs.

ATR-SEIRAS Investigation of the Fermi Level of Pt Cocatalyst on a GaN Photocatalyst for Hydrogen Evolution under Irradiation

The interaction of photogenerated carries in GaN photocatalyst with Pt cocatalyst for hydrogen evolution under irradiation was investigated from in situ ATR-SEIRAS measurement by following the CO vibrational frequency. After irradiation, the CO frequency shifted higher, indicating that the Fermi level of Pt particles was positively shifted by the photogenerated holes. Thereafter, a lower frequency peak appeared, indicating that the Fermi level of some Pt particles was negatively shifted to the hydrogen evolution potential by photogenerated electrons, which is the essential function of cocatalysis for hydrogen evolution.

DFT study of CO and NO adsorption on low index and stepped surfaces of gold

Adsorption energies and vibrational frequencies of CO and NO adsorbed on gold (1 1 1), (1 0 0), (1 1 0) and (3 1 0) surfaces, as well as on adatoms on Au(1 0 0) have been calculated using density functional theory. The results clearly show that the adsorption energy of the molecules increases considerably with increasing the degree of coordinative unsaturation of the gold atoms to which the molecules bind, and thus support the view that defects, steps and kinks on the surface determine the activity of gold catalysts.

Electric field and surface charge effects on the vibrational frequency of CO chemisorbed on metal surfaces: Cluster model studies for CO/Cu(100)

Electric field and surface charge effects on the vibrational frequency of CO chemisorbed on metal surfaces: Cluster model studies for CO/Cu(100)

First-principles calculation of the ultrafast spin manipulation of two-center metallic clusters with a CO molecule attached to one center as an infrared marker

We present a fully ab initio ultrafast spin manipulation calculation in two-magnetic-center clusters with CO attached to one of the magnetic centers. CO serves as an experimental marker for certain magnetic states between which spin flip and transfer can be achieved. The predicted spin-state-dependent CO vibrational frequencies indicate that spin manipulation can be readily monitored through the infrared spectrum. The feasibility is demonstrated by two charged clusters ${[{\text{CoMg}}_{2}\text{Ni-CO}]}^{+}$ and ${[\text{NiCo-CO}]}^{+}$. Spin transfer between magnetic centers is achieved with a fidelity of 99.8%.

Absence of CO dissociation on Mo(112)

We revisit the problem of CO adsorption and thermal dissociation on the Mo(112) surface by means of density-functional calculations of binding energies, local densities of states, and CO vibrational frequencies for various configurations of equilibrated adlayers. The bridge-on-row adsorption sites on the Mo(112) surface are found to be the most favorable and CO molecules will occupy less stable in-furrow sites only after the completing of the first monolayer. At low coverages, CO molecules are tilted by approximately 40 degrees with respect to the normal to the surface (the beta state), but with increasing coverage, due to lateral interactions, attain an upright orientation with the carbon end down (the alpha state). The tilting of CO results in a significant elongation of the C-O bond (to 1.20 A) and, consequently, the C-O stretching vibration frequency decreases to 1159 cm(-1). Nonetheless, the beta state cannot be attributed to the precursor to CO dissociation, because the estimated potential barrier for the dissociation (approximately 2.8 eV) substantially exceeds the chemisorption energy (2.1 eV), which makes the thermally induced CO dissociation on Mo improbable. With estimated chemisorption energies, Monte Carlo simulations have shown that the two-peak shape of TPD spectra can be explained without involving the CO dissociation. We predict also that the lack of dissociation can be detected in photoemission studies for CO on Mo(112) by the presence of the -23 and -7 eV peaks, characteristic of chemisorbed CO, and absence of the -18 and -5 eV peaks characteristic of adsorbed O atoms.

DFT-ONIOM study of Au/ZSM-5 catalyst: Active sites, thermodynamic and vibrational frequencies

Density functional and ONIOM calculations were carried out to investigate the possible active sites of Au(I) ion-exchanged ZSM-5 catalysts. Adsorption energies and vibrational frequencies of CO, NO, NO 2, SO 2, H 2O, NH 3, CH 3NH 2 and CH 3SH molecules were analyzed. For first time the existence of two active sites in Au/ZSM-5 is shown; one of them is responsible for the high and the other for the low CO and NO adsorption frequencies. The analysis of adsorption Δ G shows that Au(I) behaves like a soft acid; therefore, there will be a preferential adsorption of soft bases over hard bases. The interaction with NH 3 is thermodynamically very favored, mainly due to the hydrogen bond formation between the NH 3 hydrogen atoms and the oxygen atoms of the zeolitic framework.

Adsorption, Desorption, and Dissociation of CO on Tungsten(100), a DFT Study

Density functional theory (DFT) calculations have been performed to investigate the adsorption of CO on W(100) for several adsorption sites at four different surface coverages. Dissociation of CO on W(100) has been explored for two surface concentrations: 0.25 and 0.5 monolayer (ML). To establish whether the calculated structures are stable adsorption states or transition states, a complete analysis of the vibrational frequencies of CO was carried out. For coverages up to 0.5 ML, the CO adsorbs molecularly on the W(100) surface at fourfold hollow sites with the molecular axis tilted away from the surface normal by 58° with an adsorption energy of −3.00 eV. The calculated C−O stretching frequency at 0.25 ML CO coverage is 926 cm-1, in good agreement with experiments. Increasing CO coverage to 0.5 ML leads to a lower C−O stretching frequency of 847 cm-1, which is extraordinary, since it is not expected from previous experimental observations. The CO is able to dissociate very easily with activation energie...

V(CO)7+: A capped octahedral structure completes the 18-electron rule

Abstract Molecular structures, relative energies, vibrational spectra and bond dissociation energies of the seven-coordinate, 18-valence-electron vanadium carbonyl complex, V ( CO ) 7 + , are predicted theoretically. A C3v symmetry capped octahedral structure is found to be the global minimum and predicted CO vibrational frequencies range from 2023 to 2122 cm−1, generally consistent with experiment for known cationic carbonyl complexes. The lowest energy structure of V ( CO ) 6 + is also determined, a triplet D3d structure. The resulting bond dissociation energy, De, for CO ligand loss is predicted to be 11 kcal mol−1 with B3LYP, in good agreement with experiment, while BP86 and MP2 predict much higher values of 30 and 39 kcal mol−1.

Improvement of scale factors for harmonic vibrational frequency calculations using new polarization functions

AbstractDensity functional calculations were carried to improve the calculated CO vibrational frequencies for transition metal carbonyls. Two types of density functionals were studied, hybrid and generalized‐gradient methods. Using the simplex optimization method, new polarization functions for C and O atoms were obtained. With these new optimized functions, new scaling factors were obtained. The results reveal that, with the new polarization functions, the agreement between the calculated and the experimental values improves considerably. In general, the new scaling factors are very close to unit, with standard uncertainties close to ±0.006 cm−1. The use of the new polarization functions allows more precise calculations of the transition metal carbonyl CO vibrational frequencies. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008