Vibrational Relaxation Of CO Research Articles

Picosecond IR Study of UV-Induced Peroxide Decomposition: Formation and Vibrational Relaxation of CO2 in CH2Cl2 Solution

Picosecond UV pump (248.5 nm)/IR probe spectroscopy has been applied to the study of the decomposition of several aromatic diacyl peroxides, peroxycarbonates, and of a peroxyester dissolved in CH

Coupled cluster ab initio potential energy surfaces for CO . . . He and CO . . .H 2

Ab initio potential energy surfaces including the vibrational coordinate dependence are presented for CO… He and CO… H2 using the coupled cluster method with Brueckner orbitals. The interaction energy is calculated using the supermolecule approach. The calculation of rate constants for the vibrational relaxation of CO(v = 1) by He and their comparison with the experimentally measured values over the temperature range 40–300 K is used to test the accuracy of the CO… He surface. Comparison with results from an earlier surface calculated by symmetry adapted perturbation theory shows that the two surfaces have similar scattering characteristics and reproduce the experimental measurements to a similar level of accuracy. The potential surface for the CO… H2 system is presented as raw data in anticipation of future calculations.

Coupled cluster ab initio potential energy surfaces for CO… He and CO… H2

Ab initio potential energy surfaces including the vibrational coordinate dependence are presented for CO… He and CO… H2 using the coupled cluster method with Brueckner orbitals. The interaction energy is calculated using the supermolecule approach. The calculation of rate constants for the vibrational relaxation of CO(v = 1) by He and their comparison with the experimentally measured values over the temperature range 40–300 K is used to test the accuracy of the CO… He surface. Comparison with results from an earlier surface calculated by symmetry adapted perturbation theory shows that the two surfaces have similar scattering characteristics and reproduce the experimental measurements to a similar level of accuracy. The potential surface for the CO… H2 system is presented as raw data in anticipation of future calculations.

Vibrational relaxation of CO by collisions with 11He at ultracold temperatures

Quantum mechanical coupled channel scattering calculations are performed for the ro-vibrational relaxation of CO in collisions with ultracold He atoms. The van der Waals well in the interaction potential supports a number of shape resonances which significantly influence the relaxation cross sections at energies less than the well depth. Feshbach resonances are also found to occur near channel thresholds corresponding to the j=1 rotational level in the v=0 and v=1 vibrational levels. Their existence influences dramatically the limiting values of the elastic scattering cross sections and the rotational quenching rate coefficients from the j=1 level. We present complex scattering lengths for several low lying rotational levels of CO which characterize both elastic and inelastic collisions in the limit of zero temperature. Our results for the vibrational relaxation of CO (v=1) are in good agreement with available experimental and theoretical results.

Vibrational relaxation of CO 2( m, nl, p) in a CO 2N 2 mixture. Part 2: Application to a one-dimensional problem

In order to quantify the relaxation mechanism of CO 2( m, n l , p), the vibrational level populations are calculated for a particular test-case: the vibrational relaxation of a CO 2N 2 mixture along the stagnation streamline in a reentry problem. The N 2 species is chosen as a collision partner because it is a component existing in numerous gaseous mixtures (cf. Part. 1). Excitation and deexcitation processes are taken following Nickerson and Herzfeld. The Navier-Stokes code CELHYO for the simulation of hypersonic laminar viscous flows in chemical and thermal nonequilibrium is used with a new one-dimensional approach, reduction of the Navier-Stokes equations along the stagnation streamline. Mass fraction and ‘vibrational temperature’ distributions of every vibrational level, considered as an independent chemical species, are presented for the two different CO 2N 2 mixture compositions. The validity of the usual assumptions for the vibrational mechanism is examined on the basis of the obtained results.

Vibrational relaxation of CO 2 ( m, nl, p) in a CO 2-N 2 mixture. Part 1: Survey of available data

The knowledge of the vibrational relaxation reaction rates of diatomic and triatomic molecules is required for the modelling of numerous gaseous mixtures such as the Earth atmosphere (involving radiation transfer phenomena), exhaust plumes, afterbody wakes, Mars atmosphere, shock waves and chemical lasers. It enables a better understanding of the chemical reaction product rates and provides the populations of the radiating levels. In this study, we consider the few lowest vibrational levels of a CO 2-N 2 mixture and the V-T and V-V energy transfer processes between these levels. The reaction rates given by experimental and theoretical studies and by different surveys of data supplied by a bibliographic search are presented. Then, comparisons of the data available for the most important processes are shown. The usual assumptions concerning the vibrational relaxation of CO 2 ( m, n l , p) are recalled and briefly discussed.

Failure of linear mixture rule in vibrational relaxation in CO2–CF2Cl2 and CO2–C4H4S mixtures

The experimental data for the deactivation of CO2(00°1) in CO2–CF2Cl2 and CO2–C4H4S mixtures are presented in the temperature range 323–463 K for different compositions. The relaxation rate per unit pressure (Pτ)−1 showed deviations from the linear mixture rule.

Tuning the Vibrational Relaxation of CO Bound to Heme and Metalloporphyrin Complexes

Picosecond mid-infrared pump−probe experiments were used to investigate vibrational relaxation (VR, which here denotes loss of excess vibrational energy) of CO bound to synthetic heme and porphyrin complexes with different metal atoms (M = Fe, Ru, Os) and different proximal ligands (imidazoles and pyridines). Isotope effects of 13CO vs 12CO and solvent effects were also studied. A remarkable correlation between the carbonyl vibrational lifetime and the carbonyl vibrational frequency νCO is observed. The vibrational lifetime decreases as νCO decreases. The lifetime−frequency correlation is consistent with a linear relation between carbonyl vibrational relaxation rate and νCO. Hemes and porphyrins show similar lifetime−frequency correlations, but the absolute value of the VR rate in meso-tetraphenylporphyrin complexes is slightly faster than in protoporphyrin IX dimethyl ester heme complexes. The predominant VR process is shown to be intramolecular transfer from CO to heme vibrations, rather than intermolec...

Vibrational Dynamics of Carbon Monoxide at the Active Sites of Mutant Heme Proteins

Picosecond mid-IR pump-probe measurements of vibrational relaxation (VR) of CO bound to the active sites of wild-type and mutant myoglobins (Mb) reveal that an approximately linear relationship exists between the protein matrix-induced CO frequency shift and the VR rate. This relation parallels a similar linear relationship seen in a series of heme model compounds where Fe was replaced by Ru and Os. The VR rate of CO in the Mb is sensitive only to the magnitude of protein-induced carbonyl frequency shifts and apparently is not sensitive to the specific details of how the shift is induced, e.g., hydrogen bonding to CO or electrostatic interactions in the heme pocket. CO VR is insensitive to substantial changes in protein structure that do not affect the CO vibrational frequency. These observations suggest that the mechanism of carbon monoxide VR in heme proteins such as Mb occurs by through-﷿-bond anharmonic coupling, which, as shown in prior work, is also the dominant coupling in the model compounds. The experiments indicate that differing protein structures influence VR of CO bound at the active site not by opening and closing channels for vibrational energy flow from CO to the protein but by affecting the rate of energy flow from CO to heme. The rates are determined by the extent of back-bonding, which determines the magnitude of through-﷿-bond anharmonic coupling between CO and heme. The back-bonding and, therefore, the extent of anharmonic coupling are influenced by the electric fields in the heme pocket, which likely differ in the proteins studied here.

Ultrafast infrared spectroscopy in biomolecules: Active site dynamics of heme proteins

Rapid advances in the generation of intense tunable ultrashort mid-infrared (IR) laser pulses allow the use of ultrafast IR pump-probe and vibrational echo experiments to investigate the dynamics of the fundamental vibrational transition of CO bound to the active site of heme proteins. The studies were performed using a free-electron laser (FEL) and an experimental set up at the Stanford University FEL Center. These novel techniques are discussed in some detail. Pump-probe experiments on myoglobin-CO (MbCO) measure CO vibrational relaxation (VR). The VR process involves loss of vibrational excitation from CO to the protein and solvent. Infrared vibrational echoes measure CO vibrational dephasing. The quantum mechanical treatment of the force-correlation function description of vibrational dynamics in condensed phases is described briefly. A quantum mechanical treatment is needed to explain the temperature dependence of VR in Mb-CO from 10 to 300 K. A molecular-level description including elements of heme protein structure in the treatment of vibrational dynamics is also discussed. Vibrational relaxation of CO in Mb occurs on the 10−11-s time scale. VR was studied in proteins with single-site mutations, proteins from different species, and model heme compounds. A roughly linear relationship between carbonyl stretching frequency and VR rate has been observed. The dominant VR pathway is shown to involve anharmonic coupling from CO through the π-bonded network of the porphyrin, to porphyrin vibrations with frequencies > 400 cm−1. The heme protein influences VR of bound ligands at the active site primarily via altering the through π-bond coupling between CO and heme. Preliminary vibrational echo studies of the effects of protein conformational relaxation dynamics on ligand dephasing are also reported. © 1996 John Wiley & Sons, Inc.

Vibrational relaxation of CO (v=1) by inelastic collisions with 3He and 4He

Calculations of the vibrational relaxation rate constants of the CO–3He and CO–4He systems are extended to lower temperatures than in any previous calculation and a comparison made with new experimental results in the temperature range 35–295 K for CO–3He and previously published results in the range 35–2300 K for CO–4He. Both the coupled states (CS) and infinite-order sudden (IOS) approximations are used, with the self-consistent-field configuration interaction CO–He interaction potential of Diercksen and co-workers. The CS approximation is found to give a similar level of agreement with experiment for the two isotopic species, while the performance of the IOS approximation is system dependent. The discrepancy between experimental and theoretical IOS rate constants is quite different for collisions involving 3He and 4He, so that it is not profitable to compare IOS results directly with experiment for these two systems at temperatures below 300 K. The differences between the measured and the CS calculated rate constants for both the CO–4He and CO–3He systems are thought to be due predominantly to inaccuracies in the interaction potential. Relaxation rate constants for CO target molecules in collision with HD, D2 and H2 are compared with results involving 3He, 4He, and ‘‘2He,’’ revealing some systematic trends depending only on mass. However, for all hydrogen species there are marked upturns in the rate constants at low temperatures relative to those for helium atoms, while the rate constants for HD are greater than those for 3He throughout the temperature range. Calculations at small initial kinetic energies for the CO–He systems reveal an unexpected increase in relaxation cross section with reduction in kinetic energy. This implies that at very low temperatures the CO–He rate constants will show an upturn with decreasing temperature. The fact that this effect is smaller than that for the CO-hydrogen systems and occurs at lower temperatures is consistent with the shallower CO–He attractive well compared with that for CO–H2.

Electric field effects on chemisorption and vibrational relaxation of CO on Cu(100)

The effect of electric fields of electrochemical strength on the vibrational relaxation of CO on Cu(100) is studied by first principles molecular orbital calculations on cluster models. The effect of the field on the lifetimes of excited vibrations, as well as on other observables such as vibrational frequencies and infrared intensities, is consistent with the chemical nature of the metal—molecule bond changing in the presence of the field. Additionally the charge distributions and molecular orbitals obtained from the calculations are analyzed in detail to show the changes that occur. The validity of the alternative Stark effect interpretation of the field's role is explained by demonstrating that similar chemical effects are implicit within that theory.

Infrared fluorescence from a monolayer of CO on NaCl(100).

Infrared fluorescence has been observed from a monolayer of $^{13}\mathrm{C}^{16}$O on NaCl(100) following vibrational excitation of its fundamental absorption band with a pulsed CO gas laser. Direct time-domain measurements of the fluorescence reveal a lifetime of 4.3 ms. Since fluorescence occurs in the overtone region from high vibrational states, these results demonstrate that energy can be stored in the adsorbate long enough to allow vibrational up-pumping between neighboring molecules. It is suggested that the primary channel for CO vibrational relaxation is \ensuremath{\Delta}v=-1 transfer to phonons of the NaCl substrate.

Vibrational relaxation of carbon dioxide at LiF(100)

The vibrational relaxation of CO2 at LiF(100) has been investigated by monitoring infrared fluorescence from vibrationally excited molecules under conditions where they are relaxed primarily by collisions with the solid surface. The relaxation probabilities are found to be 0.65±0.10 at room temperature and 0.35±0.10 at 450 K. In order to understand better the vibrational relaxation results, angular distributions of CO2 scattered from LiF(100) were measured with a molecular beam scattering apparatus. At slow incident beam velocities, the trapping probability of CO2 at LiF(100) is essentially unity. Thus, in the vibrational relaxation measurements, where the incident velocity is even slower than in the scattering experiments, vibrational relaxation is preceded by trapping. Possible mechanisms for relaxation are discussed. Excitation of phonons in the solid and transfer of energy to other degrees of freedom of the molecule (i.e., translation, rotation, and other vibrational modes) are both plausible relaxation channels.

Study of nonequilibrium vibrational relaxation of CO 2 molecules during adiabatic expansion in a supersonic nozzle. The treanor type distribution - existence and generation

The vibrational relaxation of the CO 2 molecules in a mixture with Ar in supersonic expansion is studied. The kinetic equations considered describe the changes in the population of all the vibrational levels contained within the first six multiplets of CO 2. The energy exchange and relaxation rate constants are calculated using a modified SSH theory. Existence and creation of a Treanor-Likal'ter distribution is examined. A checking procedure was developed to show to what extent the real distribution could be approximated by the TL distribution. The particular role of the VV energy transfer in the relaxation of the polyatomic CO 2 molecules is examined. Unexpected new population inversions have been found for some intramultiplet transitions.

Electronic and vibrational relaxation of CO in Ar and Kr matrices

Vibrational progressions due to radiative decay of e 3Σ(ν′ = 0, 4, 6, 8), a′ 3Σ(ν′2,6), d 3Δ(ν′= 4, 6, 8) and a 3Π(ν′=0) to the ground state or to the a 3Π state have been observed for CO in Ar and of e 3Σ(ν′ = 4, 8) and d 3Δ(ν′ = 4, 8) for CO in Kr by selective excitation of A 1Π(ν′ = 0, … 8). The bottlenecks, the intersystem crossing and the internal conversion rate constants are explained by an intramolecular mixing of electronic states and electron-phonon coupling with the matrix. For internal conversion in the singlet states an additional matrix-induced nonadiabatic matrix element exceeding 20 cm −1 has to be postulated for Kr. A long-lived Rydberg state is observed for CO/Ar.

Experimental and theoretical studies of CO vibrational relaxation by He atoms

Rate constants for the vibrational relaxation of 12C16O(v=1) and 13C18O(v=1) by 4He and 3He over an ab initio potential surface have been calculated with a vibrational close-coupling, rotational infinite order sudden (VCC-IOS) technique. Improved experimental measurements of the relaxation of 12C16O(v=1) by 4He and new measurements of the deactivation of 13C18O(v=1) by 4He and 3He all over the temperature range 300–80 K have been carried out with a laser fluorescence method. These rate constants and existing ones for the deactivation of 12C16O by 4He over the temperature range 2300–580 K and by 3He over the temperature range 300–80 K are compared with the theoretical rate constants. The rate constants vary by over six orders of magnitude but the calculations reproduce the experimental values well. These results give evidence for the accuracy of the potential energy surface and the (IOS) technique.

Experimental and theoretical determination of rate constants for vibrational relaxation of CO 2 and CH 3F by He

Rate constants have been measured for the vibrational relaxation of CO 2 and CH 3F in the temperature range 300-150 K by the collision partners 4He and 3He. These results are compared with those calculated with a vibrational close-coupling, rotational infinite-order sudden approximation.

Distorted wave calculations of the vibrational relaxation of CO in collision with He atoms

Cross sections are calculated for vibrational relaxation of the CO/He system. The calculations use the exponential distorted wave, the distorted wave and close-coupling techniques for the vibrational motion. Rotational motion is treated with the infinite-order sudden approximation. Good agreement is shown between the distorted wave methods and the close-coupled calculations. Vibrational relaxation rate constants are calculated and compared with experimentally determined values. The distorted wave approximation is shown to provide results of useful accuracy.

Vibrational relaxation of CO(n=1) in collisions with He

We present a full ab initio study of vibrational relaxation of CO(n=1) in collisions with 3He and 4He. The vibrational coordinate dependence of the interaction potential is calculated directly. Dynamical calculations are performed within the IOS and the CS approximation. The IOS cross sections agree very well with the corresponding CS results for both He isotopes, however, the ratio IOS/CS shows a different energy behavior for 3He and 4He, respectively. The CS rates for 3He agree extremely well with the experimental relaxation rates. Although only the reduced mass is changed for 4He the agreement with experiment is less favorable in this case. It is explicitly demonstrated that the often used procedure to extract the vibrational coordinate dependence of the interaction potential from a dumbbell fit of the rigid-rotor surface is wrong for He–CO. For 3He the corresponding cross sections are 3–10 times smaller than those obtained form the ab initio potential although the vibrationally elastic parts of the interaction potential are identical.