CO Fragments Research Articles

Polarity and polarizability of alkoxyacetylenes

The dipole moment of the Csp-O bond in alkoxyacetylenes is 1.3 D and is directed toward the carbon atom. The values for the major semiaxes in the polarizability ellipsoid of the HC=CO fragment are bL=4.60 and bT=bv=2.77 A3.

Vibrational excitation and dissociative attachment of a triatomic molecule: CO2 in the collinear approximation.

The effective R-matrix model and the R-matrix propagative method applied earlier to elec- tron--diatomic-molecule scattering are extended to treat dissociative attachment of collinear triatomic molecules. To describe the vibrational excitation and dissociative attachment of ${\mathrm{CO}}_{2}$ in the 4-eV region, the nuclear dynamics is solved on a Wall-Porter potential-energy surface. A hybrid approach is developed in which the ${L}^{2}$ and R-matrix propagation methods are combined to evaluate the global R matrix. Our calculations show that it is easier to excite the symmetric mode vibrations than the asymmetric mode vibrations. Our results also show that the observed structures in the energy dependence of the dissociative attachment cross sections are due to the vibrational states of the negative ion (${\mathrm{CO}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$) and not to the vibrational states of the CO fragment.

Energy partitioning in the O −/CO 2 dissociative attachment

The 4.4 and 8.2 eV dissociative attachment bands in CO 2 were reinvestigated with particular attention to O − ion kinetic energy release. On the 4.4 eV band a structure associated with the vibrational excitation of the CO fragment was observed when only zero kinetic energy O − ions were collected. A narrower structure with a spacing of 0.10±0.01 eV, assigned to the intermediate CO 2 − was observed without ion kinetic energy discrimination. On the zero kinetic energy spectrum in the 8.2 eV region a structure associated with the vibrational excitation of the CO fragment up to ν = 21 is reported for the first time. The O − kinetic energy spectrum at the 8.2 eV band is reported, corrected for the ion optics transmission function. The 8.2 eV resonance was also observed in threshold electron energy loss spectra. It decays by ejection of a near zero energy electron into the low-lying π - π ? excited states of CO 2.

Structure and properties of phosphaketene (H–PCO): phosphorus versus oxygen protonation?

Phosphaketenes carrying bulky substituents to limit dimerization have recently been reported and for comparison the simple model phosphaketene (1) was investigated using ab initio methods. It has an E-bent structure with a CP bond length of 1.728A; and a CPH bond angle of 90.6°(using the 4-31 G basis set). This is rationalized in terms of stabilizing interactions between the PH and CO fragments so that the C–P bond is essentially a dative single bond enforced by π-back-donation. Both P and O centres carry an overall negative charge; of five possible structures of protonated HPCO considered, phosphorus protonation is unambiguously preferred and the perpendicular structure (11) calculated to be the most stable. Inclusion of polarization functions and correlation energies favours phosphorus protonation further. Also reported are the vibrational frequencies, dissociation energies of the protonated and neutral phosphaketene, and the predicted reactivity in both cycloadditions and additions of HX; comparison is made with reported experimental data where available.

Branching ratios and partition of the excess energy for the predissociation of CO+2 C̃ 2Σ+g molecular cations

He–Iα photoelectron–photoion coincidence spectroscopy is used to study the decay of CO+2 molecular cations, initially prepared in various vibrational levels of the C̃ 2Σ+g state. The branching ratios for the energetically accessible fragmentation pathways are determined. Owing to the precisely known energetics and to an accurate measurement of the kinetic energies released, the partition of the respective excess energy among internal and external degrees of freedom of the separating fragments could be established. The formation of highly rotationally excited diatomic fragments must be proposed in order to explain the experimental results. The disappearance of O+ ions in favor of CO+ fragments as soon as the energy exceeds the dissociation limit for CO+ formation is consistent with a reinterpretation of previous ab initio calculations of potential-energy surfaces. The observed branching ratio for the population of the v=0 and v=1 levels of the CO fragment can be accounted for by an application of the statistical adiabatic channel model.

Primary ion beam energy effects on secondary ion emission from Ni(001)c(2 × 2)-CO: Classical dynamics calculations and sims

The variation of the SIMS spectra of Ni(001)c(2 × 2)-CO induced by bombardment of Ar + primary ions with kinetic energy between 300 and 1200 eV has been examined in detail. The purpose of the study is to examine the influence of primary ion energy on a number of experimental observables and to test the accuracy of classical dynamics calculations for neutral particles in predicting the experimental results for ejected ions. The calculations were performed using two extreme forms of the Ar + -substrate interaction potential to examine the sensitivity of the results to the parameters that need to be included in the model. We find excellent agreement between the NiCO +/Ni + ion yield ratio measured between 300–1200 eV Ar + ion energy and the computational results if the Molière form of the ion-substrate potential is used and if the calculated results are corrected by including an image force. The calculated angular distributions of the ejected particles also agree well with those observed experimentally. From the calculations we see that the extent of CO fragmentation relative to the amount of molecular CO ejection is roughly constant in the 300–1200 eV beam energy range with a slight increase seen at lower (~ 300 eV) energies. The implications of these results are discussed in terms of our ability to study the chemistry and structure of surfaces with SIMS.

Zero kinetic energy ions in dissociative attachment on triatomic molecules: S −/OCS, O −/CO 2

The zero kinetic energy yield of S − ions in OCS and O − ions in CO 2, produced by dissociative electron attachment through the lowest shape resonance, has been measured in a quadrupole mass spectrometer with electrostatic filter for translational energy analysis. The relative cross sections for S − and O − ion formation associated with CO fragments excited up to the vibrational level υ = 4 are obtained.

Formaldehyde formation in a H2O/CO2 ice mixture under irradiation by fast ions

We report the measurement of formaldehyde (H/sub 2/CO) production in an ice mixture of equal parts of water and carbon dioxide under irradiation by fast (1.5 MeV) helium ions at temperatures of approx.9 K and above. Using isotopically labeled gases, we have observed that the formaldehyde forms about 3 times more efficiently by transfer of a carbon from CO/sub 2/ to the water than by transferring H/sub 2/ from the water to a CO fragment from the CO/sub 2/. We find the production rate of H/sub 2/C to be about 3.7 per incident ion for the ice layers used in the reported experiment (approx.1000 monolayers thick). We find no significant production of formic acid (H/sub 2/CO/sub 2/). Such experiments and results as these are important for several problems in astrophysics, including the quantiative assessment of the influences of cosmic rays in interstellar space as agents for the production of molecular species in the mantles of grains.

Unimolecular reaction paths of electronically excited species. IV. The C̃ 2Σ+g state of CO+2

The geometrical structure of the low-lying states of CO+2 has been calculated ab initio. The C̃ 2Σ+g/2A1 state is found to be slightly bent in its equilibrium geometry. A new assignment of the vibrational structure of the corresponding band in the photoelectron spectrum is suggested. State C̃ is predissociated by two competitive channels. One of them leads to O++CO, the other to CO++O. The mechanism of these predissociations involves a slow, rate-determining, intersystem crossing to a bent ã 4B1 state. The population of state ã has a choice between dissociating to O++CO fragments and undergoing a further, much faster, intersystem crossing to the ground state X̃ which dissociates to CO++O. Since radiationless transitions between X̃ and ã are relatively rapid, the state which is lower in energy (i.e., X̃) has a much larger population than the other (i.e., ã). Hence, the CO++O channel prevails as soon as it is energetically accessible. The rate-determining step of both processes is the intersystem crossing between states C̃ and ã. Its rate constant is estimated by a statistical method due to Zahr, Preston, and Miller, recasted in a simpler form. A value of about 4×107 s−1 is obtained.

UV Laser photolysis of C 3O 2 at 193 nm: Emission from electronically excited C, CO and C 2

C 3O 2 was irradiated using an ArF pulsed excimer laser at 193 nm and fluorescence from electronically excited CO and C was observed. The CO(A 1Π → X 1Σ +) fourth positive emission at 200 – 250 nm results from the production of a vibrationally excited CO (X 1Σ +) fragment which is resonantly pumped to the A 1Π( v′ = 1, 4, 7) state at 193 nm. The C(3 1P 0 → 2 1S) emission at 248 nm is attributed to a two-step process; two-photon generation of the C(2 1D) state and consequent resonant excitation of the carbon atom to the 3 1P 0 state. The C 2(d 3Π g → a 3Π u) Swan high pressure band was also observed and was attributed to the collision-induced reaction between C and C 2O.

Mass spectrometry of metal compounds: II—mass spectrometric studies of [CF3EMn(CO)4]2, [CF3EFe(CO)3]2(E = S, Se), CF3SeFe(CO)2C5H5and CF3SCr(NO)2C5H5

AbstractThe electron impact induced mass spectra of [CF3SMn(CO)4]2, [CF3SeMn(CO)4]2, [CF3SFe(CO)3]2, [CF3SeFe(CO)3]2, CF3SeFe(CO)2C5H5and CF3SCr(NO)2C5H5are reported. These compounds exhibit weak molecular ion peaks and undergo preferential loss of CO or NO groups. The CO or NO free fragments suffer typical loss of ECF2(E = S, Se) with the simultaneous shift of F from carbon to metal. The ions [FFeC5H5]+and [FCrC5H5]+in the spectra of the cyclopentadienyl compounds prefer expulsion of π‐cyclopentadienyls. The pyrolysis effects on the spectra of the compounds have been studied. An increase in temperature eases the expulsion of ECF2groups from all the compounds and favors the formation of [Fe(C5H5)2]+and [Cr(C5H5)2]+in the cyclopentadienyl compounds.

Time-resolved C2 swan emission from short-pulse UV fragmentation of CO: evidence for two C2 formation mechanisms

We have studied C2 Swan (d3Π → a3 Πu) emission resulting from multiphoton UV excitation of CO. Population of d3Π proceeds through distinct early and late processes, the former giving rise only to normal Swan emission. The late process is responsible for v = 6 enhancement (high-pressure bands), and it dominates time-averaged emission in an bands for ⪖ 10 Torr of CO.

The electron energy loss spectrum of isocyanic acid on the Pt(111) surface

High-resolution, electroh energy loss spectra (EELS) and temperature-programmed desorption (TPD) spectra show that isocyanic acid is molecularly adsorbed in multilayers on the Pt(111) surface at 100 K. Heating to 150 K desorbs the multilayers and shifts the asymmetric v a (NCO) vibrational frequency from 2270 to 2160 cm −1, but the adsorption remains molecular. By 250 K, most of the isocyanic acid has decomposed on the platinum surface to form CO and nitrogen-containing surface fragments. No CO 2, H 2O, or HCN is found to desorb from the surface, and we find no evidence for cleavage of the bond between the carbon and oxygen atoms. The data indicate that an “isocyanate” species is unlikely to be stable on a platinum surface above room temperature under low-pressure conditions. Also, isocyanates on supported platinum catalysts are probably formed by the reaction of CO with a nitrogen species on the surface.

Photodissociation of triatomic molecules: Application of the R-matrix propagation methods to the calculation of bound-free Franck–Condon factors

We present a method for calculating Franck–Condon factors for the photodissociation of triatomic molecules. We use the R-matrix propagation techniques developed by Light and Walker for reactive scattering processes. The method is used to study the collinear dissociation of a model CO2 system. Franck–Condon overlaps are calculated for three different initial states and probabilities for populating particular vibrational levels of the CO fragments are obtained. We present results for a range of photon energies. We find that the partial cross sections exhibit a series of resonant or Fano line shapes. The structure in the cross sections depends sensitively on the initial vibrational state, but the peak values are not significantly effected.

A classical trajectory study of the reaction H + HCO→H2+ CO

Classical trajectories have been calculated for the reaction H + HCO → H2 + CO using an analytical potential for the ground state surface. Reactive cross sections have been obtained at 300, 500 and 1000 K. From the 300 K results an approximate rate constant has been obtained of 2·6 × 10-10 cm3 s-1 molecule-1. 90 per cent of the total energy released appears in the H2 fragment, 30 per cent vibrational, 12 per cent rotational and 48 per cent translational. The vibrational energy is approximately a Boltzmann distribution. Most of the CO fragments are in the ground vibrational state. The angular distribution of products is close to isotropic because most reactive trajectories pass through a complex with high angular momentum. This complex is a planar quadrilateral with the atoms HHCO in cyclic order and HHC > 90°. A few reactive trajectories pass through the equilibrium formaldehyde structure but we have found none which pass through the hydroxymethylene structure.

Dissociation of metal carbonyls by metastable rare gases: Fe and Ni emission analysis

Chemiluminescence from Ni(CO)4 and Fe(CO)5 collisions with metastable He, Ne, and Ar atoms is described. The emission spectra are due to atomic Ni and Fe. An analysis of these spectra indicate a dissociative energy transfer process which is not spin–differentiated among the metal atom states. Because of this, certain low-lying quintet states are seen here in emission for the first time. Steady state population analysis of all features permits a determination of the radiative lifetimes of these new states. For both carbonyls, a restricted statistical rate theory, in which the CO fragments are allowed to translate in one dimension only (the radial reaction coordinate) and are prohibited from rotating, gives good agreement with all the data. The nature of metastable electronic energy transfer is compared to photolytic energization, and a comparison of the likely excited electronic states involved in each indicates the source of the differences in product distributions observed by each method.

A classical trajectory study of the fragmentation of CO−2 2Σ+g

The dissociation of the 2Σ+g CO−2 ions formed by electron attachment is studied with a classical trajectory method in which the initial conditions are represented by the Wigner probability density function and the electronic state 2Σ+g of CO−2 is described by a Wall–Porter potential energy surface. Since both the ground initial state of CO2 and the upper dissociative state of CO−2 have an equilibrium angle of 180°, the dissociation is studied through the collinear approximation. The experimental data (excess energy transferred to vibration, population inversion of the vibrational CO levels) are found to be related not only to the autodetachment rate as usual, but also to some details of the repulsive potential energy surface such as the position and height of the saddlepoint and to the inertial coupling between translation and vibration.

Metal—metal bonding in dinuclear complexes of platinum(I). The crystal and molecular structure of carbonyl(chloro)-bis-μ-[bis(diphenylphosphino)methane]diplatinum hexafluorophosphate

The structure of [Pt 2Cl(CO) (μ-Ph 2PCH 2PPh 2) 2] [PF 6] was determined by X -ray methods and refined to R = 0.082, using diffractometric intensities of 5646 independent reflections. The crystals are monoclinic, space group P 2 1/ n , a = 12.919(3), b = 15.576(6), c = 25.151(5)Å, β = 94.82(3)°, Z = 4. They are built of octahedral hexafluorophosphate anions and dinuclear platinum(I) cations. The latter contain PtCl and PtCO fragments linked to one another by a PtPt σ-bond and by two bridging bis(diphenylphosphino)methane ligands. The platinum atoms are in square planar environments and the dihedral angle between the two coordination planes is 40.1°. Selected bond lengths are: PtPt 2.620(1), PtCl 2.384(5), PtC 1.89(3) and PtP 2.291(5) – 2.308(5)Å.

Atomic hydrogen in the giant molecular cloud near M17

The giant molecular cloud extending parallel to the galactic plane southwest of M17 to 85 pc is investigated in the H I 21-cm absorption line by use of the Maryland-Green Bank Survey. The H2/H I abundance ratio is estimated to be 830 and 450 for two of the CO fragments. An anomalous region, characterized by a large line width of about 10 km/s and two-dip profiles, is found near the southwestern edge of the cloud. These findings are examined in the light of current theories on chemical evolution of dark clouds and on cloud formation. It is suggested that in the preshock region, cloud fragments appear to line up in order of age as in the postshock region represented by OB subgroups. Cloud-cloud collisions induced by a galactic density wave may play an important role in the formation of the giant cloud.

Dynamics of three-body half collisions. I. Secondary product decomposition in the photodissociation of acetyl iodide

Photofragment spectroscopy of acetyl iodide (CH3COI) at 266 nm shows evidence of a two-step dissociation into three products. Initial photodissociation yields an iodine atom and a highly internally excited acetyl radical containing on average 80% of the energy available in the dissociation process. The transition dipole moment of the initial absorption lies in the C–C–O plane near the C–I bond axis, and breakup of the photoexcited acetyl iodide is rapid, on the order of 10−13 sec. The acetyl fragment is found to live for several rotational periods, ∼10−11 sec. Its subsequent decomposition to CO and CH3 can be modeled by statistical theories of unimolecular decay. It is found that an average 30% of the energy residing in the acetyl radical ultimately appears as relative translational energy of the CO and CH3 fragments.