Excited CO Molecules Research Articles

Sonochemical Disproportionation of Carbon Monoxide in Water: Evidence for Treanor Effect during Multibubble Cavitation

A sound reaction: The ultrasonically driven disproportionation of CO in water causes formation of hydrated polymer of carbon suboxide (C3O2)n (see picture) enriched with a heavy 13C isotope. This finding indicates the presence of vibrationally excited CO molecules with a non-equilibrium Treanor distribution inside the cavitating bubble.

Isotope effect in Boudouard disproportionation reaction in optically pumped CO

Isotope composition of CO 2 produced in CO–Ar mixtures optically pumped by a CO laser has been analyzed by Fourier transform infrared (FTIR) absorption spectroscopy. Carbon monoxide reactant is a higher-than-natural abundance mixture of 13CO and 12CO. Carbon monoxide in the reactor is vibrationally excited by resonance absorption of the laser radiation and is vibration–vibration (V–V) pumped up to high vibrational levels. 12CO vibrational level populations and temperature in the excited region are measured by FTIR emission spectroscopy. Highly vibrationally excited CO molecules chemically react to form CO 2, which at these conditions is expected to be enriched in 13C isotope. Chemical reaction products are analyzed by FTIR absorption spectroscopy. The results show that CO 2 in the products is enriched in 13C isotope, with enrichment coefficient varying from β = 1.25 to 1.9, and CO 2 yield varying from 70 to 170 ppm. These results are in good agreement with the master equation kinetic model.

Vibrational to electronic energy transfer from CO to C 2 molecules

The paper discusses the experimental results pointing to the efficient channel of the CO vibrational to the C 2 electronic energy transfer. The radiation spectra of the d 3П g, e 3П g, C 1П g electronic states of C 2 molecule are investigated and the relation of their kinetics to a vibrational excitation of CO molecules in the He–CO–O 2 plasma is discussed. The changes of CO vibrational energy distribution (VED) were imposed by an application of a laser resonator to the discharge tube under investigation. It was found that the modulation of laser radiation (and VED) led to a similar changes of the spontaneous radiation from d 3П g, e 3П g and C 1П g states of C 2 molecules.

Vibrational relaxation of highly excited CO molecules on CO2 molecules in the active medium of a CO laser

The stationary vibrational distribution functions (VDFs) of CO molecules are measured in the axial region of a glow discharge in a glass tube at different concentrations of CO2 molecules. The relaxation constants of CO(v) molecules in excited vibrational states colliding with CO2 molecules are estimated for high vibrational levels with v = 17–29 by comparing experimental and calculated VDFs of CO molecules. Mechanisms explaining large relaxation rates are discussed. The dependence of the emission spectrum of a CO laser on the concentration of CO2 molecules is studied experimentally.

Trapping of molecules by highly rotational excitations

Desorption of vibrationally excited CO molecules from NaCl surface has been studied more than a decade ago in experiments of Chang and Ewing [H.C. Chang, G.E. Ewing, Chem. Phys. 139 (1989) 55]. Surprisingly, the desorption process was found to be inefficient (longer than 102 s) although the van der Waals type complex CO–NaCl has enough energy to break the weak CO–NaCl bond (i.e., to get the CO molecules off the solid surface). The present paper gives a clear theoretical explanation of this phenomenon. Namely, our calculations based on complex scaling show that the vibrational excitation energy of CO is transferred into its rotational motion, while the coupling between the rovibrational degrees of freedom of CO and the surface is suppressed. Thereby, the highly rotationally excited CO molecule is trapped on the solid surface practically forever and forms a bound state in the continuum. This type of trapping mechanism is not specific to the interaction between adsorbed molecules and the surfaces of ionic crystals only, and might be applicable to other systems and to other type of experiments.

Yield of excited CO molecules from dissociative recombination of HCO+ and HOC+ ions with electrons

The authors have investigated CO band emissions arising from the dissociative recombination of HCO(+) and HOC(+) ions with thermal electrons in a flowing afterglow plasma. The quantitative analysis of the band intensities showed that HCO(+) recombination forms the long-lived CO(a (3)Pi) state with a yield of 0.23+/-0.12, while HOC(+) recombination favors formation of CO(a' (3)Sigma(+)) and CO(d (3)Delta) with a combined yield of greater than 0.4. The observed vibrational distribution for the CO(a) state reproduces theoretical predictions quite well. The vibrational distributions for CO(a') and CO(d) are, in part, inverted, presumably as a consequence of a change in CO equilibrium bond length during recombination. The observations are compatible with current knowledge of the potential surfaces of states of HCO and HCO(+).

A laser for dismantling reactors and hardening rails

Laser-based methods are known to be more efficient than traditional approaches for a range of tasks that include dismantling obsolete nuclear reactors, maintaining railroad tracks in good working condition, stimulating chemical reactions, and separating isotopes. Among the attractions of lasers are fewer byproducts, increased reactor cutting speed, enhanced lifetime and capacity of the railway, and the ability to deal with toxic agents without igniting them. Moreover, laser techniques are more effective than other methods in processing radioactive waste. Realizing these capabilities takes a high-power laser with superior optical quality. Acceptable cost and efficiency are additional requirements. High-power CO2 lasers are commercially available; however, they are expensive and inefficient, and suffer from deteriorating optical quality as power increases. Alternatives include so-called chemical oxygen-iodine lasers (COILs) and CO lasers. But the COIL, too, is expensive, and there is as yet no industrial prototype. And although NUPEC Corporation, in Tokyo, Japan, has impressively demonstrated a 20kW CO laser for cutting large arrays of steel pipes and plates,1 the system lacks an optical cable of transferring CO radiation. Furthermore, the laser requires cryogenic components, which adds to its cost. We propose a CO laser2 that dispenses with the need for an optical cable by installing the laser head on the manipulator. Our concept is based on the discharge of stable homogeneous radio frequency (RF) in a supersonic stream and the demonstration of laser generation in a small-scale experimental installation.3 We also devised a computational model for scaling the CO laser with RF discharge. Supersonic expansion makes it possible to obtain the required cryogenic temperatures, and the RF discharge enables us to get optimal parameters for vibrational excitation of CO molecules without an electronic gun. The reduced ratio of the electric field to gas density (E/N) in a column of gas is stated in the literature.4, 5 With our model, we can calculate the power parameters of the CO laser and optimize them to obtain high values of output power and efficiency. The cost of the laser is kept low through use of standard elements, for example, compressor, RF generator, and power station. Owing to the high density of the gas in front of the supersonic nozzle of the laser head and behind the supersonic diffuser, the closed contour serves as a pipeline that enables flexible positioning of the laser head, for example, on the manipulator. Consequently, no optical cable is needed to transfer laser radiation. A standard compressor can be used because values such as pressure and Mach number can be maintained in a stream that makes it possible to restore pressure upon an input in the compressor up to 1atm. Themodel consists of calculations of RF discharge parameters, vibrational kinetic equations, and dynamic gas equations that describe a supersonic stream in the RF discharge zone. We have considered low-current RF discharge with electron photoemission from the electrode surface and injection of electrons from electrode sheaths in a positive column. A low-current RF discharge is realized when the ratio of the time required for the ions to drift through the sheath and reach the electrode to the period of the RF field is much larger than unity.6, 7 Thus, the electrode sheaths have no time to break up and exist simultaneously at both electrodes. Plausible applications for the CO laser include dismantling obsolete nuclear reactors and hardening of the surfaces of railway rails. Our next step will be to test the laser in applications involving toxic agents, in processing radioactive waste by extracting ruthenium, and separating isotopes of heavy hydrogen and uranium. These applications can be extended substantially only once the laser is commercially available.

Gas-phase Boudouard disproportionation reaction between highly vibrationally excited CO molecules

The gas-phase Boudouard disproportionation reaction between two highly vibrationally excited CO molecules in the ground electronic state has been studied in optically pumped CO. The gas temperature and the CO vibrational level populations in the reaction region, as well as the CO 2 concentration in the reaction products have been measured using FTIR emission and absorption spectroscopy. The results demonstrate that CO 2 formation in the optically pumped reactor is controlled by the high CO vibrational level populations, rather than by CO partial pressure or by flow temperature. The disproportionation reaction rate constant has been determined from the measured CO 2 and CO concentrations using the perfectly stirred reactor (PSR) approximation. The reaction activation energy, 11.6 ± 0.3 eV (close to the CO dissociation energy of 11.09 eV), was evaluated using the statistical transition state theory, by comparing the dependence of the measured CO 2 concentration and of the calculated reaction rate constant on helium partial pressure. The disproportionation reaction rate constant measured at the present conditions is k f = (9 ± 4) × 10 −18 cm 3/s. The reaction rate constants obtained from the experimental measurements and from the transition state theory are in good agreement.

On the theory of the reaction rate of vibrationally excited CO molecules with OH radicals

The dependence of the rate of the reaction CO+OH-->H+CO2 on the CO-vibrational excitation is treated here theoretically. Both the Rice-Ramsperger-Kassel-Marcus (RRKM) rate constant kRRKM and a nonstatistical modification knon [W.-C. Chen and R. A. Marcus, J. Chem. Phys. 123, 094307 (2005).] are used in the analysis. The experimentally measured rate constant shows an apparent (large error bars) decrease with increasing CO-vibrational temperature Tv over the range of Tv's studied, 298-1800 K. Both kRRKM(Tv) and knon(Tv) show the same trend over the Tv-range studied, but the knon(Tv) vs Tv plot shows a larger effect. The various trends can be understood in simple terms. The calculated rate constant kv decreases with increasing CO vibrational quantum number v, on going from v=0 to v=1, by factors of 1.5 and 3 in the RRKM and nonstatistical calculations, respectively. It then increases when v is increased further. These results can be regarded as a prediction when v state-selected rate constants become available.

Effect of the vibrational excitation of CO molecules on the parameters of an RF discharge

A one-dimensional model of an RF discharge in CO-containing gas mixtures is developed. The model takes into account the effect of the degree of vibrational excitation of CO molecules on the structure of the discharge and on its parameters. Experimental data are presented from measurements of the voltage-power characteristics of RF discharges in gas mixtures with different CO contents in the pressure range of 10–100 torr. The model developed is used to calculate the dependence of the root-mean-square discharge voltage on the specific power deposition in an RF discharge under our experimental conditions. The experimental data are compared to the results of numerical simulations. For working gas pressures of about 100 torr, which are typical of the operation of slab CO lasers, the calculated voltage-power characteristics of an RF discharge agree satisfactorily with those obtained experimentally. The theoretical model predicts that the vibrational excitation of CO molecules leads to a redistribution of the RF field in the discharge gap and to an increase in the laser efficiency.

Vibrational energy exchanges between N2 and strongly excited CO molecules: their role in vibrational kinetics

The rate constants for multiquantum vibration-to-vibration (V-V′) energy exchanges in CO(v)–N2(v′) collisions, with CO in highly excited vibrational levels v and N2 in the first few low-lying vibrational levels, were obtained from ab initio semiclassical calculations. A large temperature interval was explored, T = 100–500 K, while the vibrational quantum numbers v and v′ were in the range v = (30–44) and v′ = (0–3). The role played by these collisional processes in the vibrational kinetics of CO:Ar/He:N2 gas mixtures under typical laser conditions were explored in detail by using a recently developed kinetic modelling procedure. In particular, it was found that the V-V′ exchanges between CO and N2 exert an essential influence on the time evolution of the vibrational population and on the associated small signal gain and spectral characteristics of the CO laser in both the fundamental and overtone bands.

Possibility of revealing the role of nonresonant energy exchange between electrons and CO molecules at high vibrational levels

An experimental method providing information about the interaction of electrons with excited CO molecules at high vibrational levels is proposed and justified theoretically. The suggested experimental scheme is based on the use of two successive discharge pulses under the conditions prevailing in an electroionization CO laser. The first pulse should ensure a sufficiently high energy input in order for a nonequilibrium vibrational distribution function to form. The second pulse serves to study the effect of the electric current on the vibrational distribution function of excited molecules at high vibrational levels. The theoretical analysis is based on the simultaneous solution of the Boltzmann equation for the electron energy distribution function and the vibrational kinetic equations realistically describing the multiquantum vibrational-vibrational exchange processes. The calculated results show that the sensitivity of the proposed measurement technique promises to be high.

Vibrational excitation of CO molecules by infrared free electron laser

This paper describes the vibrational excitation of CO molecules by FEL-SUT (Free Electron Laser at Tokyo University of Science). FEL is tuned to 4.67 μm, corresponding to the X 1Σ +( v″=1)←( v″=0) transition of CO. The population of the vibrationally excited states is probed by the (2+1) resonance enhanced multiphoton ionization technique via the B 1Σ + Rydberg state. We find that ∼10% of the population in v″=0 is excited to v″=1. In spite of the existence of the resonant vibrational ladder climbing channels via specific rotational levels, no signal originating from v″=2 is detectable. The predissociation in the B 1Σ +( v′=2) state is believed to be responsible for the absence of CO + signals.

Rotational and Vibrational Excitation of CO Molecules by Collisions with4He Atoms

Full close-coupled calculations are carried out of the cross sections for energy transfer between rotational levels of carbon monoxide in collision with 4He atoms with energies between 5 and 600 cm-1. At low energies, the cross sections are dominated by contributions from shape resonances. The calculated cross sections are in satisfactory agreement with the experimental data measured at an energy of 570 cm-1. Calculations using the infinite order sudden approximation are carried out of cross sections for energy transfer between vibrational levels of CO. Vibrational energy transfer is dominated by transitions in which the vibrational quantum number changes by unity.

Electron-mediated vibration–electronic (V–E) energy transfer in optically pumped plasmas

The paper discusses experiments on vibration-to-electronic energy transfer in CO laser pumped CO–Ar and CO–N 2 plasmas. Ionization in these strongly nonequilibrium plasmas occurs by an associative mechanism, in collisions of two highly vibrationally excited CO molecules. The experiments show that removal of the electrons from the optically pumped plasmas using a saturated Thomson discharge results in considerable reduction of the UV/visible radiation from the plasma (CO 4th positive bands, NO γ bands, CN violet bands, and C 2 Swan bands). At some conditions, the removal of electrons results in a nearly complete extinguishing of the UV/visible glow of the plasma. This effect occurs even though electron removal results in an increase of the high vibrational level populations of the ground electronic state CO(X 1 Σ, v∼15–35). On the other hand, deliberate electron density increase by adding small amounts of O 2 or NO to the optically pumped CO–Ar plasmas produced a substantial increase of the UV/visible radiation intensity, which strongly correlates with the electron density. The results of the present experiments indicate that the vibration-to-electronic (V–E) energy transfer process CO( X 1Σ→ A 1Π ), and, possibly, analogous processes populating radiating excited electronic states of NO, CN, and C 2, in optically pumped plasmas, may be mediated by the presence of electrons which are created in the absence of an electric field, with low initial energies. Most importantly, this effect occurs at ionization fractions as low as n e/ N∼10 −9–10 −7.

Vibrational relaxation of vibrationally and rotationally excited CO molecules by He atoms

This work presents a detailed quantum mechanical study of rovibrationally inelastic He+CO collisions in a wide range of translational and internal energies of the collision partners. Fully converged coupled states calculations of rate constants for vibrational relaxation of CO(v=1) by He are found to be in excellent agreement with experimental measurements at temperatures between 35 and 1500 K. The role of rotational energy for vibrational relaxation of CO is investigated and it is illustrated that the CO molecules in the first excited vibrational state can exhibit near-resonant vibrational relaxation when they are initially in high rotational excitation and the collision energy is small. A reduced channel coupled states approach neglecting low vibrational states in the basis set is implemented for calculations of rate constants for vibrational and rotational energy transfer in collisions of vibrationally excited CO molecules with He atoms. It is shown that initial vibrational excitation significantly increases rate constants for vibrationally inelastic collisions but does not affect purely rotational energy transfer.

Quenching of vibrationally excited CO( ν=2) molecules by ultra-cold collisions with 4He atoms

The quenching of vibrational excited CO( ν=2) molecules by He atoms at ultra-low temperature is examined to determine the relative efficiency of the processes that involve the exchange of a double or a single quantum of vibrational energy. We find that at low temperature the double quantum exchange cross-section is orders of magnitude smaller than for the single quantum process. This result is valid for different initial rotational states of the CO molecule.

Carbon Monoxide Production and Excitation in Comet C/1995 O1 (Hale-Bopp): Isolation of Native and Distributed CO Sources

The release of carbon monoxide from Comet C/1995 O1 Hale-Bopp was studied between June 1996 and September 1997 using high resolution infrared spectroscopy near 4.7 μm. The excitation of CO molecules in the coma was assessed through measurement of the rotational temperature on several dates at an angular resolution of ∼1 arcsecond. An increase in T rot with distance from the nucleus was revealed, most likely because of photolytic heating by fast H-atoms. Observed temperature profiles varied from date to date, but overall the degree of heating was most pronounced near perihelion. The similar rotational temperatures observed for CO and HCN may indicate control of rotational populations by collisions with electrons. The spatial distribution of CO molecules in the coma revealed two distinct sources for CO, one being CO ice native to the nucleus, and another being CO released from a progenitor distributed in the coma. Only the native source was seen when the comet was beyond 2 AU from the Sun. Based on pre- and post-perihelion observations on five dates with heliocentric distance R h between 4.10 and 2.02 AU, a heliocentric dependence Q CO,native=(1.06±0.44)×10 30 R h −1.76±0.26 molecules s −1 was obtained. Within R h∼1.5 AU, however, both native and distributed sources were consistently present on all dates of observation. The total CO produced was the sum of the two sources and, based on seven dates, obeyed Q CO,total=(2.07±0.20)×10 30 R h −1.66±0.22 molecules s −1. This heliocentric dependence was consistent with that found for water (Q H 2O αR h −1.88±0.18 between 0.93 and 1.49 AU) and for mm-sized dust (R h −1.7±0.2 between 0.9 and 2.5 AU). Our derived total mixing ratio for CO was Q CO,total/Q H 2O =0.241±0.009, with native and distributed sources each contributing an abundance of approximately 12 percent that of water. This was the case even after correcting measured CO and H 2O column densities, and hence production rates, for opacity in the solar pump. The distributed source exhibited behavior consistent with thermal destruction of a precursor material. The observed variations in its production rate and spatial distribution along the slit suggested contributions from both a diffuse source in the coma and possibly from one or more jets enriched in CO or CO-containing material, such as CHON grains.

Theoretical modelling and experimental studies of the multi-quantumvibration exchange in vibrationally excited CO molecules

Studies of the vibration-vibration (VV) exchange in COmolecules excited up to vibration quantum numbers v = 20 have beenperformed both theoretically and experimentally. A new kinetic model whichtakes into account the multi-quantum VV exchange in the temperature rangeT = 100-300 K is described for the first time. A description is given ofthe experimental methodology allowing for studies of the effects of therelaxation of the vibrational distribution after a sudden disturbance. Thedisturbance of the vibrational distribution is produced by a Q-switchedshort pulse of single line radiation in fundamental band. The relaxationis studied by measuring the laser pulse energy of the second pulseinitiated by resonator Q-switching produced with a variable time delayrelative to the first pulse. A set of kinetic rate constants accepted inthe model for various gas temperatures, vibration level numbers and numberof exchanged vibration quanta from 1 to 4 is presented. The good agreementbetween the experimental data and the results of the advanced theory isthe first direct evidence in support of the multi-quantum exchange model.

Radio frequency energy coupling to high-pressure optically pumped nonequilibrium plasmas

This article presents an experimental demonstration of a high-pressure unconditionally stable nonequilibrium molecular plasma sustained by a combination of a continuous wave CO laser and a sub-breakdown radio frequency (rf) electric field. The plasma is sustained in a CO/N2 mixture containing trace amounts of NO or O2 at pressures of P=0.4–1.2 atm. The initial ionization of the gases is produced by an associative ionization mechanism in collisions of two CO molecules excited to high vibrational levels by resonance absorption of the CO laser radiation with subsequent vibration-vibration (V-V) pumping. Further vibrational excitation of both CO and N2 is produced by free electrons heated by the applied rf field, which in turn produces additional ionization of these species by the associative ionization mechanism. In the present experiments, the reduced electric field, E/N, is sufficiently low to preclude field-induced electron impact ionization. Unconditional stability of the resultant cold molecular plasma is enabled by the negative feedback between gas heating and the associative ionization rate. Trace amounts of nitric oxide or oxygen added to the baseline CO/N2 gas mixture considerably reduce the electron–ion dissociative recombination rate and thereby significantly increase the initial electron density. This allows triggering of the rf power coupling to the vibrational energy modes of the gas mixture. Vibrational level populations of CO and N2 are monitored by infrared emission spectroscopy and spontaneous Raman spectroscopy. The experiments demonstrate that the use of a sub-breakdown rf field in addition to the CO laser allows an increase of the plasma volume by about an order of magnitude. Also, CO infrared emission spectra show that with the rf voltage turned on the number of vibrationally excited CO molecules along the line of sight increase by a factor of 3–7. Finally, spontaneous Raman spectra of N2 show that with the rf voltage the vibrational temperature of nitrogen increases by up to 30%. This novel energy efficient approach allows sustaining large-volume high-pressure molecular plasmas without the use of a high-power CO laser. This opens a possibility of using the present technique for high-yield plasma chemical synthesis and plasma material processing.