Neutral CO Molecule Research Articles

Nonsequential and Sequential Fragmentation ofCO23+in Intense Laser Fields

We experimentally studied the three-body fragmentation dynamics of CO(2) initiated by intense femtosecond laser pulses. Sequential and nonsequential fragmentations were precisely separated and identified for CO(2)(3+) to break up into O(+) + C(+) + O(+) ions. With accurate measurements of three-dimensional momentum vectors of the correlated atomic ions and calculations of the high-level ab initio potential of CO(2)(3+), we reconstructed the geometric structure of CO(2)(3+) before fragmentation, which turns out to be very close to that of the neutral CO(2) molecule before laser irradiation. Our study indicated that Coulomb explosion is a promising approach for imaging geometric structures of polyatomic molecules if the fragmentation dynamics can be clearly clarified and the appropriate dissociation potential is provided for multiply charged molecular ions.

First rate coefficients for an interstellar anion: application to the CN−-H2 collisional system

Recently, several molecular anions have been detected in the interstellar medium. Accurate modelling of their microwave emission spectra requires the calculation of rates for rotational excitations by collisions with the most abundant species. We report the first collisional data for an interstellar anion, the rate coefficients for the rotational excitation of CN− by H2. State-to-state rate coefficients between the 11 lowest rotational levels of CN− were calculated for temperatures ranging from 5 to 100 K. Collisions with para- and ortho-H2 are taken into account. The CN− rate coefficients are compared with those of the neutral CO molecule, and, as expected, it is found that the rate coefficients for the anion are significantly larger than those of the neutral species. The new set of rate coefficients will help significantly in the interpretation of the CN− emission lines observed with current and future telescopes, and enable this molecule to become a powerful astrophysical tool.

Competition of electron transfer, dissociation, and bond-forming processes in the reaction of the CO22+ dication with neutral CO2

The bimolecular reactivity of the CO(2)(2+) dication with neutral CO(2) is investigated using triple quadrupole and ion-ion coincidence mass spectrometry. Crucial for product analysis is the use of appropriate isotope labelling in the quadrupole experiments in order to distinguish the different reactive pathways. The main reaction corresponds to single-electron transfer from the neutral reagent to the dication, i.e. CO(2)(2+) + CO(2) --> 2CO(2)(+); this process is exothermic by almost 10 eV, if ground state monocations are formed. Interestingly, the results indicate that the CO(2)(+) ion formed when the dication accepts an electron dissociates far more readily than the CO(2)(+) ion formed from the neutral CO(2) molecule. This differentiation of the two CO(2)(+) products is rationalized by showing that the population of the key dissociative states of the CO(2)(+) monocation will be favoured from the CO(2)(2+) dication rather than from neutral CO(2). In addition, two bond-forming reactions are observed as minor channels, one of which leads to CO(+) and O(2)(+) as ionic products and the other affords a long-lived C(2)O(3)(2+) dication.

Decomposition of Neutral, Singly and Doubly Protonated Benzoquinone in the Gas Phase

The unimolecular fragmentations of singly and doubly protonated ortho-, meta-, and para-benzoquinones (BQH(+) and BQH(2)(2+), respectively) are studied by tandem mass spectrometry. The dominant fragmentation pathways lead to the elimination of a neutral CO molecule from BQH(+) and, by charge separation, to the expulsion of protonated CO from BQH(2)(2+). Reaction mechanisms are elucidated based on labeling experiments and UB3 LYP calculations. These results reveal that the respective reactions proceed in an analogous fashion to the decarbonylation of neutral benzoquinones, which decompose into carbon monoxide and cyclopentadienone. Single protonation facilitates all steps on the reaction pathway with neutral CO and O-protonated cyclopentadienone as final products. In contrast, double protonation leads to an increase of the barriers for the decomposition yielding CO.H(+) and O-protonated cyclopentadienone. This major process of BQH(2)(2+) is accompanied by two minor channels, which lead to the elimination of neutral carbon monoxide and water, respectively. The proton affinity of the para-BQH(+) monocation is estimated as 3.6+/-0.3 eV.

Substituent Effects in the Unimolecular Fragmentation of Anisole Dication Derivatives

The unimolecular fragmentation of metastable anisole dications is studied by tandem-mass spectrometry. Permutations of OH, OCH3, and NH2 substituents as well as extensive labeling experiments are used as probes to unravel the mechanisms of the various fragmentation pathways observed. The main channel corresponds to methyl ion elimination, which leads to an energetically favorable charge separation (“Coulomb explosion”). Loss of a neutral CO molecule forms another important branch, and the expelled CO has incorporated a carbon atom from the phenyl ring of anisole. Substitution of the anisole dication with OH, OCH3, and NH2 groups results in more specific fragmentations. Ortho- and para-substitutions lead to preferential methyl ion elimination, whereas meta-substitution favors CO loss. The substituent effects are also reflected in pronounced changes in the apparent kinetic isotope effects upon substitution of OCH3 by OCD3. On the basis of the various experimental findings and some explorative DFT calculations, possible mechanisms for the skeletal rearrangements prior to CO elimination are proposed.

Associative electron stimulated desorption of neutral CO molecules

The Electron Stimulated Desorption (ESD) of neutral CO molecules was studied on polycrystalline Ni surface. Combined ESD and temperature programmed desorption (TPD) measurements were used to observe the variations of neutral ESD yield in dependence on CO coverage, containing direct information about the cross section for ESD of neutral CO molecules in relation to various CO adsorption states. The results show evidence of ESD of neutral CO molecules from dissociative adsorption states. The cross section for this associative ESD process is relatively high in comparison with the CO ESD cross section for molecular CO adsorption.

Identification of Emissions in the Spectrum of Comet C/1989 VI (Skoritchenko–George) Obtained with the 6-m SAO RAS Reflector

The emission spectrum of comet Skoritchenko–George (C/1989 VI), unusual in its information content, was obtained on February 26.7 UT, 1990, with the use of a TV scanner installed on the 6-m BTA reflector of the Special Astronomical Observatory of the Russian Academy of Sciences (SAO RAS) in Nizhni Arkhyz. Detailed identification of the emission lines of this comet was made. The observed spectrum contains 311 emission lines, including those of the \({\text{C}}_{\text{2}} {\text{,C}}_{\text{3}} {\text{,CN,NH,CH,Na,NH}}_{\text{2}} {\text{,CO,CO}}^{\text{ + }} {\text{,CO}}_{\text{2}}^{\text{ + }} {\text{,CH}}^{\text{ + }} {\text{,N}}_{\text{2}}^{\text{ + }} {\text{,H}}_{\text{2}} {\text{O}}^{\text{ + }} {\text{,}}\;{\text{and}}\;{\text{C}}_{\text{2}}^{\text{ - }}\) molecules. Among others, the lines of the negative carbon C 2 - ion and the lines corresponding to the electron transition \(e^3 \sum ^ - - a^3 \prod _r\) in the neutral CO molecule are discovered. The presence of a large number of lines of the neutral CO molecule (the Asundi bands and the triplet bands) in the visible region is one of the uncommon features of the emission spectrum of this comet. The triplet lines \(d^3 \Delta - a^3 \prod _r\): 15–3, 13–2, 11–2, 9–1, 8–1, 7–1, 7–0, 5–0, 4–0; \(e^3 \sum ^ - - a^3 \prod _r\): 7–0, 6–0, 5–0; and a"\(a'^3 \sum ^ + - a^3 \prod _r\): 11–1 (K = 3, 4); 16–4 (K= 0, 1, 2, 4); 9-0 (K= 0, 1, 2); 8–0 (K= 0) were identified for the first time. Prior to this work, the lines of CO in the visible range were observed only in the spectrum of comet C/1979 VI (Bradfield) in 1989.

Measurement of 10−1 s state-specific lifetimes in the neutral CO molecule

Recently, a technique has been demonstrated which allows the measurement of metastable lifetimes in neutral molecules of up to 10−3 s [J. Chem. Phys. 110, 6319 (1999)]. The present article extends the method by two orders-of-magnitude to molecular lifetimes as long as 10−1 s. Using the CO metastable a 3Π state, lifetimes of eight rovibrational a 3Π(v=3,Ω,J) levels were measured. Within their experimental error of 30%, these lifetimes agree with previous theoretical predictions [J. Chem. Phys. 110, 6319 (1999)]. The presented technique is suggested for identification of molecular quintet states, in particular the CO a″ 5Π state.

Guided ion beam investigation of the reaction CO++CO: C–O bond activation and C–C bond formation

We have investigated six different endothermic channels in the reaction of CO+ ions with neutral CO. For each ionic product we have measured the kinetic energy dependence of the integral cross section and inferred the neutral products by the reaction energetics. The onset of the process producing C+, O, and CO, has been identified by a feature of the integral cross section located at about 8.5 eV. Measurements of the product isotopic ratio suggest that C+ originates from both the CO+ ion and the neutral CO molecule. For the reaction channels producing C2++O2 and C2O++O, respectively, measurements of the reaction thresholds allow us to estimate the heats of formation of these two ionic products, ΔfH0(C2+)=19.8±0.2 eV and ΔfH0(C2O+)=14.7±0.2 eV. These values are in good agreement with recent independent estimations. Finally, we re-evaluated the dissociation energy of C2+(X 4Σg−), D0(C+–C)=6.2±0.2 eV.

Luminosity of the triplet band of neutral CO molecules in the atmosphere of comet Scorichenko-george (1990 VI)

Abstract Identification of the Asundi and Triplet bands of neutral CO molecules in the spectra of comets Bradfield (1980 XV) (Cosmovici et al., 1982) and Scorichenko-George (1990 VI) (Churyumov, 1992) puts on the agenda decoding the real physical mechanism of the luminosity of the cometary CO in the visual spectral range. The results of the identification of the Triplet bands in the comet Scorichenko-George spectra, obtained with the TV-spectral scanner of the 6-m BTA reflector, are given. The g-factors of the CO molecule are calculated for the Triplet system d 3Δ i -a 3Π r (λλ 3770–7500 A) and for the Asundi band a 13Σ+ - a 3Π r (λλ 3900–8600 A). The flux of radiation, connected with the fluorescent excitation of the upper states d 3Δ i and a 13Σ+ from the x 1Σ+ ground state by the solar UV radiation, is sufficiently small. This confirms Biermann's (1976) supposition that if CO Triplet bands are observed in comets, the mentioned mechanism cannot be the single cause of their appearance.

Dissociation of multicharged CO molecular ions produced in collisions with 97-MeV Ar14+: Total-kinetic-energy distributions.

Transient molecular ions of CO{sup {ital q}+} (where {ital q}=2--7) were produced in single collisions of 97-MeV Ar{sup 14+} projectiles with neutral CO molecules. The resulting dissociation products were identified by coincidence time-of-flight spectroscopy in which the time of flight of the first ion to reach the detector and the time difference between the first ion and its partner were recorded event by event. An iterative matrix-transformation procedure was employed to convert the time-difference spectra for the prominent dissociation channels into total-kinetic-energy distributions. Analysis of the total-kinetic-energy distributions and comparisons with the available data for CO{sup 2+} and CO{sup 3+} from synchrotron radiation experiments led to the conclusion that ionization by Ar-ion impact populates states having considerably higher excitation energies than those accessed by photoionization.

Chemical pseudoexcitation of the CO ligand and vibrational frequences of transition metal carbonyls

The forward- and back-donations of electrons between the CO ligand and central transition element atom lead to a system of cumulated multiple bonds of the type X=Y=Z. From a "vibrational" point of view this fact means a non-separability of vibrational motions of the three MCO nuclei. A coupling of the stretching vibrations ν1(MC) and ν3(CO) leads to analogous fundamental frequencies as in the case of the isolated stable molecules of O=C=O, S=C=O, Se=C=O, etc. The magnitude of the vibrational coupling between ν1 and ν3 is roughly proportional to the fundamental frequency of the degenerated deformation vibration ν2ab of the MCO grouping, i.e. a ratio of the frequencies should be constant. With free molecules of CO2, SCO, CS2, N2O and others, the ratio (ν1 + ν3)/ν2ab of the fundamental frequencies is equal to 5.5 like with complex anions [(CO)PtX3]- regardless X = Cl, Br or I. For other transition metal carbonyls the ratio is within the range of 4.0-6.0. On the other hand, the H3B-C=O molecule as a system with the essentially single B-C and the triple C=O bond is characterized by a markedly different value (9.0). In the latter, the local electronic state of CO is similar to the electronic ground state of the positive ion CO+ of the free molecule. In the transition metal carbonyls the chemical pseudoexcitation of the CO ligand leads to its local electronic states which are similar to electronic excited states lying between an excited valence state of the free neutral CO molecule (back-donation is equal to one electron) and an excited valence state of the free negative ion CO- (back-donation is equal to two electrons.

Mass spectrometric study of conjugated bifunctional acetylenes: 2—Ynals and ynones

AbstractThis study is based on results obtained by new techniques for observing metastable ions which make it possible to determine the fragmentation paths of conjugated ynals and ynones. For the ynals, the most interesting fragment is the [M–28]+˙ ion. For the ynones, when a McLafferty rearrangement is feasible, the ion arising therefrom is more abundant than the [MCO]+. ion. However, this elimination of a neutral CO molecule is quite important for the true acetylene ketones.

Heterogeneous photocatalysis I. The influence of oxidizing and reducing gases on the electrical conductivity of dark and illuminated zinc oxide surfaces

Since the photoconductivity of zinc oxide increases with time in a carbon monoxide atmosphere and also during the subsequent evacuation under light, it must be concluded that the uptake of CO by an illuminated zinc oxide surface is understandable only if neutral CO molecules react with chemisorbed oxygen to form CO O −(ads). The decreased photoconductivity of zinc oxide due to introduction of carbon monoxide in oxygen confirms this mechanism and leads to the further assumption that a considerable portion of the chemisorbed oxygen must be present as O 2 −(ads). This assumption also explains why the half-life period t 1 2 of the dark decay in pure oxygen is proportional to 1 p O 2 The generation of charge carriers during the illumination is strongly influenced by doping zinc oxide with Li 2O and Ga 2O 3. Possible mechanisms are discussed. Since an addition of Li 2O to zinc oxide changes neither the position nor the intensity of the green luminescence band, it remains uncertain whether the donors, reacting with the electronic species, are responsible for the green luminescence light.

The third positive carbon and associated bands

The band spectra associated with carbon are numerous and many of then were known to the earliest workers in spectroscopy. They divided the bands into two main divisions, the positive and the negative bands. Thus they recognised the first positive carbon bands which are now called the Swan bands, the second positive bands which we now call the Ångström bands, the third positive and the fourth positive carbon bands, Among the negative bands known to them were the first negative or Deslandres' bands which are now known to be due to the ionised CO (CO + ) molecule. With the exception of the first positive bands or Swan bands, all the positive bands are now attributed to the neutral CO molecule. In recent years several new band systems have been added to the positive list, and two, the comet-tail bands or low pressure carbon bands, and the Baldet-Johnson combination bands, to the negative band systems. The history of the correlation of all these band systems is an interesting one and is adequate proof of the extraordinary usefulness of the quantum theory in the interpretation of molecular spectra. In this paper we are mainly concerned with the third positive carbon bands and such other bands as are usually associated with them. These bands were originally measured by Deslandres. Wolter could not obtain some of them which therefore were considered as spurious. Johnson and Birge gave the quantum interpretation of these bands, which fell into three n " progressions, viz., n' = 0, 1 and 4, the last two being spurious according to Wolter. Duffendack and Fox proved that the bands forming the n' = 4 progression belong to a new system of bands which they called 3A, with an initial electronic level higher than that of the third positive bands. All these bands have been obtained on all the plates taken in the first order of a 21-foot Rowland grating, by the present writer. The superficial structure of all the bands forming the same n" progression is the same but differs from the structure of the rest of the bands. It is therefore suggested that the bands forming the n" = 1 progression also arise from an initial electronic level different from that of the third positive bands. These may be called the 5 B bands. It is scarcely necessary to say that all these band systems have the same final electronic level.