M. Matti Maricq

Experimental and theoretical study of the vibrational relaxation of CO(ν = 1) and N2(ν = 1): V-T relaxation by the isotopes of helium

Abstract Experimental results are reported for the rate constants for the vibrational relaxation of CO(ν = 1), 14 N 2 (ν = 1) and 15 N 2 (ν = 1) by 3 He and 4 He in the temperature range from 300-80 K. These are compared to rate constants determined from the numerical solution of the quantum scattering equations. It is shown that the infinite-order sudden approximation can be used to reduce the number of coupled channels to those required for the vibrational levels. The calculations are applied to ab initio potentials and a model based on the anisotropic Morse potential. The major features which govern the rate of vibrational deactivation are shown to be the energy of the vibrational quantum, the mass of the collision partner and the steepness of the repulsive part of the intermolecular potential. Including an attractive well in the potential preferentially increases the relaxation rate constants at low temperatures. The roles of the attractive terms and the anisotropy of the potential in the deviations of the experimental data from the Landau-Teller predictions are discussed.

Vibrational autodetachment of NO

We report infrared cross sections for the photodetachment of the molecular anion NO− in the energy range of 1100–1500 cm−1. The measurements are made with a coaxial ion beam–laser beam aparatus. We observe a vibrational autodetachment resonance centered at 1284±10 cm−1. The resonance has a full width at half‐maximum of 170 cm−1 corresponding to a lifetime of 0.35×10−12 s for NO−(v=1). The present value for the vibrational frequency of NO− is significantly lower than previous estimates obtained from photoelectron spectroscopy of NO− and from electron scattering resonances in NO. We discuss the implications of our results with regard to previous measurements of infrared photodetachment cross sections in the region 3000–4100 cm−1.

Vibrational relaxation of gaseous CO(v=1) and N2(v=1) from 300 K to liquid temperatures: A comparison with liquid state relaxation

The V–V energy transfer rate constants are reported for the deactivation of both CO(v=1) and N2(v=1) by O2 and CH4 in the temperature range 300 to 80 K. The results are obtained by an infrared fluorescence technique. In order to study the relaxation of N2(v=1), a small amount of CO is added to the gas mixture to function both as a pump and a probe. The probability vs temperature curves obtained are approximately parallel for the deactivation of CO(v=1) as compared to that of N2(v=1). This temperature dependence is found to resemble that for the V‐T deactivation of CO at low temperatures. This is due to the large mismatch for these V–V energy transfer processes. The rate constants at liquid N2 temperatures are compared with rate constants measured by other researchers for relaxation of the same systems in the liquid phase. The results show that the relaxation rate constants, expressed in terms of cm3u2009s−1 molecule−1, are approximately equal in the two phases. The implications of this result with respect to ...

Influence of mileage accumulation on the particle mass and number emissions of two gasoline direct injection vehicles.

Gasoline direct injection (GDI) is a new engine technology intended to improve fuel economy and greenhouse gas emissions as required by recently enacted legislative and environmental regulations. The development of this technology must also ensure that these vehicles meet new LEV III and Tier 3 emissions standards as they phase in between 2017 and 2021. The aim of the present paper is to examine, at least for a small set, how the PM emissions from GDI vehicles change over their lifetime. The paper reports particle mass and number emissions of two GDI vehicles as a function of mileage up to 150K miles. These vehicles exhibit PM emissions that are near or below the upcoming 3 mg/mi FTP and 10 mg/mi US06 mass standards with little, if any, deterioration over 150K miles. Particle number emissions roughly follow the previously observed 2 × 10(12) particles/mg correlation between solid particle number and PM mass. They remained between the interim and final EU stage 6 solid particle count standard for gasoline vehicles throughout the mileage accumulation study. These examples demonstrate feasibility to meet near-term 3 mg/mi and interim EU solid particle number standards, but continued development is needed to ensure that this continues as further fuel economy improvements are made.

Convergence of the Magnus expansion for time dependent two level systems

This paper derives criteria for the convergence of the Magnus expansion, applied to an arbitrary time dependent two level system, in terms of the eigenvalues of the Hamiltonian for that system. When a weak to moderate intensity field perturbs a two level system the resonance frequency of the system must lie below the frequency of the applied field for the series to converge. An alternative solution for the exponential form of the evolution operator is developed that converges for all values of the expansion parameter and clearly shows the singularities that lead to the failure of the Magnus solution. Finally, a simple unitary transformation is presented that extends considerably the radius convergence of the Magnus series, as illustrated by a spin 1/2 in a linearly polarized field.

Non-resonant V—V energy transfer between diatomic molecules at low temperatures

Abstract Theoretical and experimental values are compared for the rate constants of energy transfer between the υ = 1 vibrational levels of two non-polar molecules. Eight pairs of collision partners composed from the molecules CO, N 2 , and O 2 , and their isotopic derivatives, are studied in the temperature range 300-70 K. The distorted-wave and infinite-order-sudden approximations are used to calculate the inelastic cross sections using both an ab initio potential (for N 2 ue5f8N 2 ) and an empirical Morse potential. A single set of parameters for the Morse potential is able to fit very well the experimental values for all eight systems. We draw the conclusion that the V—V energy transfer is physically nearly identical to the V—T relaxation of a diatomic molecule by an atom. The dynamics are dominated by the energy that must be converted into translation as a consequence of the collision. Therefore, the shape of the repulsive part of the intermolecular potential, the reduced mass of the collision partners, and the energy defect play the major roles in determining the energy transfer probability. A nearly linear relationship is found to exist between log k and the energy defect.

A modified landau-teller model for vibrational relaxation of small molecular ions

Abstract We report a new interpretation of vibrational relaxation of molecular ions based on a modified Landau-Teller model. Distorted wave calculations show the relaxation to be dominated by repulsive forces. The ion-induced-dipole forces alter the steepness of the repulsive force and increase the effective collision energy. Incorporating these modifications into the Landau-Teller model correctly predicts the observed dependence of the cross sections on collision energy.

The effects of water vapor on the CH3O2 self-reaction and reaction with HO2.

The gas phase reactions of CH3O2 + CH3O2, HO2 + HO2, and CH3O2 + HO2 in the presence of water vapor have been studied at temperatures between 263 and 303 K using laser flash photolysis coupled with UV time-resolved absorption detection at 220 and 260 nm. Water vapor concentrations were quantified using tunable diode laser spectroscopy operating in the mid-IR. The HO2 self-reaction rate constant is significantly enhanced by water vapor, consistent with what others have reported, whereas the CH3O2 self-reaction and the cross-reaction (CH3O2 + HO2) rate constants are nearly unaffected. The enhancement in the HO2 self-reaction rate coefficient occurs because of the formation of a strongly bound (6.9 kcal mol(-1)) HO2 x H2O complex during the reaction mechanism where the H2O acts as an energy chaperone. The nominal impact of water vapor on the CH3O2 self-reaction rate coefficient is consistent with recent high level ab initio calculations that predict a weakly bound CH3O2 x H2O complex (2.3 kcal mol(-1)). The smaller binding energy of the CH3O2 x H2O complex does not favor its formation and consequent participation in the methyl peroxy self-reaction mechanism.

A comparison of rate constants for vibrational relaxation in liquid argon and in the gas phase at the same temperature

Abstract Rate constants for non-resonant VV transfer from 12 CO( v = 1) to O 2 , CH 4 and N 2 ; from 13 CO( v = 1) to O 2 and N 2 ; and from N 2 ( v = 1) to CH 4 have been measured in liquid-argon solutions at 85 K. The results are compared with those obtained in the gas phase at the same temperature in this laboratory. In all cases the rate constants are the same in both phases within 10%. These results are at variance with the predictions of cell theory and cannot be accounted for adequately by the statistical theory of Delalande and Gale. Calculations are presented which show that collisions with remarkably low energies of ≈ 100 cm −1 (150 K) dominate the energy transfer processes at these low temperatures. However it is concluded that the isolated binary collision model is still applicable.

Application of a folding transformation to the Magnus solution for the evolution of periodically time dependent systems

Two difficulties arise in the Magnus expansion for the evolution operator of a periodic time dependent Hamiltonian when the eigenvalues of the Hamiltonian are separated by more than 2π/τ, where τ is the period: (1) The Magnus expansion generally does not converge, and (2) the equilibrium properties of the system cannot be determined by statistical mechanical techniques analogous to those for time independent systems. A transformation is introduced that folds the eigenvalue spectrum into the interval −π/τ<λi<π/τ, yet retains the periodicity of the Hamiltonian, thereby alleviating the above difficulties. The method is compared to the approach taken by Shirley [Phys. Rev. B 138, 979 (1965)] for the Floquet solution to the evolution operator. It is applied to a dipole coupled spin system in an oscillating transverse field and the implications of the folding transformation on the spin thermodynamics of this system and the ‘‘Magnus paradox’’ are discussed.