Angular distribution of the photoelectron spectrum of CO2, COS,CS2, N2O,H2O,and H2S

The photoelectron spectra of the triatomic molecules CO₂, COS, CS₂, N₂O, H₂O, and H₂S have been measured as a function of the angle θ between the direction of the incoming photon and outgoing photoelectron. The photoelectron spectra have been measured with a double-focusing electrostatic electron spectrometer to which has been attached a chamber containing a gas discharge lamp that can be freely rotated. (The photon source used was the 21.22 eV He I resonance line). From the dependence of intensity as a function of θ the angular parameter β was determined for each ionization band observed in the photoelectron spectra. A correlation was noted between the values of β and the molecular orbitals relative to the contributions of oxygen and sulfur atomic orbitals. Individual β values were also obtained for most of the vibrational bands seen in the photoelectron spectra. In most cases the vibrational structure showed little or no change in the angular parameter for a given electronic state. In certain cases, however, such as the fourth ionization band in CS₂, CO₂, and COS, rather sizeable changes in β were observed for the different vibrational bands.     

Adsorption of CO on Ni-promoted TiO2(110)

The valence-band structure and the vibrational modes of CO adsorbed on nickel-promoted TiO₂(110) surfaces as a function of CO exposure have been studied by means of ultraviolet photoelectron spectroscopy (UPS) and high-resolution electron energy-loss spectroscopy (HREELS). It is found that CO exists in molecular form at room temperature on the nickel-promoted TiO₂(110) surfaces and most likely binds to the Ni atoms or nickel-affected sites rather than to the substrate atoms. At saturation coverage, CO molecules adsorb simultaneously on the 2-fold bridge sites and terminal sites on the (111)-oriented Ni islands deposited upon TiO₂(110). The occupation of the edge sites of Ni islands gives rise to an anomalously low frequency of the C---O stretching vibration. This frequency, indicative of a weakened C---O bond, suggests existence of a precursor to the dissociated state.     

Vibrationally resolved K-shell photoionization of CO with circularly polarized light

Diffraction of a low energy (<4 eV) carbon-K-photoelectron wave that is created inside a CO molecule by absorption of a circularly polarized photon is investigated. The measurements resolve the vibrational states of the K-shell ionized CO+ molecule and display the photoelectron diffraction patterns in the molecular frame. These show significant variation for the different vibrational states. This effect is stronger than predicted by state-of-the-art theory. As this study is performed close to C-K-threshold and, therefore, far below the molecule's sigma-shape resonance, this surprisingly strong effect is not related to that resonance phenomenon.     

Photon-induced thermal desorption of CO from small metal-carbonyl clusters

Thermal CO desorption from photoexcited free metal-carbonyl clusters has been resolved in real time using two-color pump-probe photoelectron spectroscopy. Sequential energy dissipation steps between the initial photoexcitation and the final desorption event, e.g., electron relaxation and thermalization, have been resolved for Au2(CO)(-) and Pt2(CO)5-. The desorption rates for the two clusters differ considerably due to the different numbers of vibrational degrees of freedom. The unimolecular CO-desorption thresholds of Au2(CO)(-) and Pt2(CO)5- have been approximated by means of a statistical Rice-Ramsperger-Kassel calculation using the experimentally derived desorption rate constants.     

On the interpretation of the photoelectron spectrum of CO chemisorbed on Ni

A LCAO-SCF calculation on the NiCO molecule is reported. In addition to the ionization potentials the vibrational structure due to ionization is calculated. The computed ionization potentials are compared with those of recent semiempirical calculations on the CO — Ni system and with the photoelectron spectra of CO chemisorbed on nickel surfaces. We produce further evidence that the first peak in the photoelectron spectrum relates to the 5σ and 1π orbitals of CO and that the peak at higher ionization energy represents the 4σ orbital.     

Observation and assignment of the first photoelectron band of the CH3CO (XA) radical

HeI photoelectron spectra have been recorded for the reaction of fluorine atoms with acetaldehyde at different reaction times. A structured band associated with a short-lived primary reaction product was recorded at a reactant mixing distance of 6 mm above the photon beam. The vertical ionization energy was measured as (8.39 ± 0.05 eV), and regularly spaced vibrational structure was observed in this band with an average vibrational separation of (1605 ± 30 cm⁻¹). The band was assigned to ionization of the CH₃CO (X²A) radical on the basis of first vertical ionization energies computed for the two possible primary products, CH₃CO and CH₂CHO, using ab-initio calculations. The calculations carried out on CH₃CO (X²A), and its singlet ground cationic state, revealed that the observed vibrational structure can be assigned to excitation of the CO stretching mode in the ion. The measured adiabatic ionization energy, 7.21 ± 0.05 eV, is higher than the value expected (6.94 ± 0.03 eV) from evidence in the literature and calculated values in this work. This difference is assigned to poor Franck–Condon factors in the region of the band onset which means that the true adiabatic ionization energy was not observed.     

Intermolecular vibrational relaxation upon multiphoton excitation of triplet molecules by a CO2 laser

Intermolecular vibrational relaxation is studied in mixtures of polyatomic molecules (benzophenone and fluorene) with bath gases after multiphoton excitation of the triplet molecules by CO₂ laser radiation. The dependences of the decay rate and the intensity of laser-induced delayed fluorescence on the laser energy density E _CO2 and pressure P _fg of bath gases are analyzed. They are found to be different for the fast and slow components of delayed fluorescence, which decays nonexponentially. It is shown that a change in the decay rate of the fast fluorescence component with increasing pressure P _fg is governed by the properties of vibration-translation relaxation. The efficiency β of this process is estimated in a broad range of vibrational energies. It is found that β weakly changes with increasing E _vib upon excitation of molecules to high vibrational levels. The features of intermolecular vibrational relaxation at high densities of anharmonically coupled vibrational states are discussed.     

A TDS and HREELS study of CO adsorbed on a potassium promoted Fe(111) surface

The adsorption behavior of CO on a potassium promoted Fe(111) surface was investigated in the range from zero to several monolayers of preadsorbed potassium. TD spectra show that the presence of potassium decreases the amount of CO which is desorbed in the α (molecular) desorption state and increases the desorption temperature of this state. In addition, it gives rise to second, β (recombination) desorption state which is correlated to K desorption. The total CO uptake is comparable to that for the clean surface for precoverages of up to one monolayer, beyond this, however, it increases and at three potassium monolayers it is about twice the clean surface value. At K precoverages above 0.5 monolayer the initial sticking coefficient for CO is greatly reduced so that CO exposures of up to several thousand Langmuirs are required in order to saturate the surface. The three stretch frequencies which are observed in HREELS for CO adsorbed on clean Fe(111) are all affected by the presence of potassium. At potassium precoverages between zero and 0.5 monolayers these frequencies shift both in energy and relative intensity; however, between 0.5 and 1 preadsorbed potassium monolayers the spectra are greatly modified and now show only two losses in the CO stretch region. The lower-frequency one of these gives evidence for a close interaction of CO with the coadsorbed potassium.     

碱金属碳酸盐的拉曼光谱研究

报导了用高温激光Raman光谱仪测定了不同温度 (至 1 2 73K)下固体和熔融态的Li2 CO3、Na2 CO3和K2 CO3的Raman光谱 ,分析了CO2 -3 对称伸缩振动模随温度升高的波数移动情况和半高宽的变化 ,结合前人的振动光谱和X射线测试结果以及分子动力学模拟工作 ,讨论了碳酸盐熔体的结构特征 ,以及不同的碱金属离子对碳酸根离子的振动造成的不同影响     

Influence of the electronic structure on chemisorbed CO

The chemisorption of carbon monoxide on amorphous and crystalline alloys such as Pd-Si, Ni---Zr, Ir---Si, and Pd---U---Si has been studied by ultraviolet photoelectron spectroscopy (UPS). Systematic trends in the CO chemisorption behavior have been found for the various alloy systems. A correlation between the position of the valence band d-electron states of the LTM (late transition metals) and the molecular orbitals of the chemisorbed CO molecules is reported. The influence of the substrate electron states on the C-O bond strength is explained in a qualitative model involving the symmetry and the binding energy of the substrate valence electrons and those of the molecular orbitals.     

ESCA study of carbon monoxide and oxygen adsorption on tungsten

The chemisorption of both CO and O₂ on a clean tungsten ribbon has been studied using an ultrahigh vacuum X-ray photoelectron spectrometer. For CO, the energy and intensity of photoemission from O(1s) and C(1s) core levels have been studied for various adsorption temperatures.At adsorption temperatures of ～100 K., the “virgin”-CO state was the dominant adsorbed species. Conversion of this state to more strongly-bound β-CO is observed upon heating the adsorbed layer to ～320K. Thermal desorption of CO at 300?T?640 K causes sequential loss of α₁-CO and α₂-CO as judged by the disappearance of O(1s) and C(1s) photoelectron peaks characteristic of these states.Oxygen adsorption at 300K gives a single main O(ls) peak at all coverages, although at high oxygen coverages there exist small auxiliary peaks at ～2eV lower kinetic energy. The photoelectron C(1s) and O(1s) binding energies observed for these adsorbed species are all lower than for gaseous molecules containing C and O atoms. For CO adsorption states there is a systematic decrease in photoelectron binding energy as the strength of adsorption increases. These observations are in general accord with expectations based on electronic relaxation effects in condensed materials.     

The angular behaviour of electrons inelastically scattered from the shape resonance for CO chemisorbed on Ni(110)

Recent vibrational high resolution electron energy loss experiments (HREELS) have shown evidence for molecular shape resonances in the inelastic scattering of electrons from chemisorbed molecules. Such resonances arise from the capture of the incident electron in a quasibound state of the molecule, leading to the formation of a temporary negative ion. They are manifest as an enhancement in the intensity of a specific vibrational mode at a characteristic incident electron energy. In contrast to gaseous species, the alignment which the surface provides for the chemisorbed species, can be exploited to determine the angular characteristics of the resonant state. In this work, we show evidence for a shape resonance, centred at an incident energy of 18 eV, for CO/Ni(110). The angular dependence of the scattered electron intensity has been measured for the CO stretching vibration. The results are discussed in terms of the spherical harmonic components of the resonant state, modified by vibrational broadening caused by low frequency bending modes associated with the bonding of the CO molecule to the surface.     

Low-energy vibrational excitation cross section of multilayers of CO molecules on graphite using electron scattering

This paper presents a low-energy study of the vibrational excitation cross section of 50 layers of CO molecules on graphite at 23 K using the electron energy loss spectroscopy technique. The vibrational excitation cross section or the excitation curve is presented for two different scattering angles. The results show an energy dependence of the vibrational excitation cross section, at both angles, which indicates the formation of negative ion resonance in this adsorbed phase of CO on graphite. The data show an oscillatory structure in the region between 0.5 and 3 eV that is associated with the excitation of the ²Π state.     

Study of adsorption states and interactions of CO on evaporated noble metal surfaces by infrared absorption spectroscopy: II. Gold and copper

We have used infrared absorption spectroscopy to study the adsorption of CO at low temperature on evaporated films of gold and copper as a function of the coverage of CO and the deposition temperature of the metal. For both metals we observe two distinct adsorption regimes when the cold metal is exposed to CO gas. These regimes arise depending on whether the deposition temperature of the metal (or the highest temperature at which the metal has been annealed) is above or below a threshold temperature. Gold films deposited at temperatures below 290 K contain chemically active sites at which CO chemisorbs, while films deposited at higher temperatures do not support CO chemisorption. This behavior is very similar to that observed on silver films. Chemisorption of CO occurs on copper films regardless of deposition temperature, but the vibrational spectrum is radically different for films deposited above and below the threshold temperature of 250 K. For both metals, the shift of the vibrational frequency with CO coverage has been analyzed, and the static and dynamic contributions separated. The dynamic shift is found to be well modeled by dipole-dipole coupling, with no evidence for vibrational coupling through the metal. An analysis of infrared intensities and vibrational polarizabilities shows no evidence for any special infrared enhancement analogous to the large enhancement in Raman cross section peculiar to adsorption on rough metal films, particularly noble metal films, deposited at low temperatures.     

The coadsorption of potassium and co on the pt(111) crystal surface: A TDS,HREELS and UPS study

The interaction of CO with a potassium covered Pt(111) surface is investigated using thermal desorption (TDS), high resolution electron energy loss (HREELS) and ultraviolet photoelectron (UPS) spectroscopies. When submonolayer amounts of potassium are preadsorbed, the adsorption energy of CO increases from 25 to 36 kcal/mole, while substantial shifts in the site occupancy from the linear to the bridged site are observed. The CO stretching vibrational frequencies are shown to decrease continuously with either increasing potassium coverage or decreasing CO coverage. A minimum CO stretching frequency of 1400 cm^?1 is observed, indicative of a CO bond order of 1.5. The work function decreases by up to 4.5 eV at submonolayer potassium coverages, but then increases by 1.5 eV upon CO co-adsorption. The results indicate that the large adsorption energy, vibrational frequency and work function changes are due to molecular CO adsorption with a substantial charge donation from potassium through the platinum substrate and into the 2π¹_CO orbital.     

Infrared spectrum of the CO-OCS van der Waals complex in the carbon monoxide stretching band

The rotation-vibration band of the weakly bound OCS-CO complex which corresponds to the carbon monoxide CO vibrational mode has been detected using a pulsed supersonic slit-jet expansion and a tunable infrared diode laser probe. The band was found to have a parallel (δK _a = 0) structure, in good agreement with previous determinations of the structure of the complex. Its rotational structure appeared to be affected by numerous small (～ 0.01 cm^?1) perturbations in the upper state which probably are due to interactions with bound levels of a lower lying vibrational state of the complex. The band origin is located with a relatively small shift of + 1.23 cm^?1 from that of the free CO molecule.     

Photoelectron angular distributions from H2 and D2

The photoelectron asymmetry parameters of H₂ and D₂ have been measured using synchrotron radiation over the photon energy range 19–27 eV. The results are compared with previous measurements and several theoretical calculations. A few of the theoretical calculations are in good agreement with experiment, but most of them predict asymmetries which are too large. Essentially identical β values were measured for H₂ and D₂. This result is discussed in terms of differences which could arise due to vibrational and rotational structure.     

Torsion-vibration interaction in CH3OH

The strong torsion-vibration interaction in CH₃OH has traditionally been dealt with by letting the torsional barrier height depend on vibrational excitation, and letting the vibrational energy depend on torsional excitation. By including an explicit interaction term in the Hamiltonian this is avoided, and apart from an anomaly which is presumably caused by the OH bending mode, the relative location of the vibrational ground state and the CO stretch state is well reproduced for torsional states n = 0, 1, and 2 by adjusting a single interaction constant.     

Oxygen chemisorption and the carbon monoxide-oxygen interaction on Ru(101)

The adsorption of oxygen and the interaction of carbon monoxide with oxygen on Ru(101) have been studied by LEED, Auger spectroscopy and thermal desorption. Oxygen chemisorbs at 300 K via a precursor state and with an initial sticking probability of ~0.004, the enthalpy of adsorption being ~300 kJ mol^?1. As coverage increases a well ordered ¦11,30¦ phase is formed which at higher coverages undergoes compression along [010] to form a ¦21,50¦ structure, and the surface eventually saturates at 0 ~ $\text{8}\text{9}$. Incorporation of oxygen into the subsurface region of the crystal leads to drastic changes in the surface chemistry of CO. A new high; temperature peak (γ CO, E_d ~ 800 kJ mol^?1) appears in the desorption spectra, in addition to the α and β CO peaks which are characteristic of the clean surface. Coadsorption experiments using ¹⁸O₂ indicate that γ CO is not dissociatively adsorbed, and this species is also shown to be in competition with β CO for a common adsorption site. The unusual temperature dependence of the LEED intensities of the ¦11,30¦-O phase and the nature of α, β, and β CO are discussed. Oxygen does not displace adsorbed CO at 300 K and the converse is also true, neither do any Eley-Rideal or Langmuir-Hinshelwood reactions occur under these conditions. Such processes do occur at higher temperatures, and in particular the reaction CO(g) + O(a) → CO₂(g) appears to occur with much greater collisional efficiency than on Ru(001). The oxidation of CO has been examined under steady state conditions, and the reaction was found to proceed with an apparent activation energy of 39 kJ mol^?. This result rules out the commonly accepted explanation that CO desorption is rate determining, and is compared with the findings of other authors.