A Classical Trajectory Calculation of Average Energy Transfer Parameters for the CH3OO+Ar System

1989 ◽  
Vol 42 (8) ◽  
pp. 1227 ◽  
Author(s):  
AR Whyte ◽  
RG Gilbert
Keyword(s):  
Internal Energy ◽  
Average Energy ◽  
Classical Trajectory ◽  
Rate Coefficients ◽  
Vibrationally Excited ◽  
Temperature Ranges ◽  
Molecular Potentials ◽  
Dissociation Threshold ◽  
Temperature And Pressure ◽  
Trajectory Simulations

A newly developed method is used to calculate the average energy transferred in collisions between a highly vibrationally excited methylperoxy radical and argon bath gas. The method involves modelling the process through classical trajectory simulations with accurate intra- and inter-molecular potentials. These calculations show that the root-mean-squared internal energy transferred per collision is c. 275 cm-1 for 300 ≤ T/K ≤ 600 (the CH302 internal energy being 104 cm-1, the dissociation threshold), while the same quantity for rotational energy is c. 290 cm-l. These results make it possible for rate data obtained by other workers for the reaction CH3O2+M ↔ CH3+02+M over limited pressure and temperature ranges to be used to predict reliably the appropriate rate coefficients at any temperature and pressure.

Dynamics of collisional dissociation: I 2 in Ar and Xe

1974 ◽  
Vol 341 (1624) ◽  
pp. 105-119 ◽  
Keyword(s):  
Internal Energy ◽  
Cross Sections ◽  
Classical Trajectory ◽  
Dissociation Rate ◽  
Rate Coefficients ◽  
Release Mechanism ◽  
Dissociation Limit ◽  
Recombination Reaction ◽  
Importance Sampling Techniques ◽  
Equilibrium Dissociation

The dynamics of collision induced dissociation of I 2 in Xe and Ar was investigated between 300 and 3500 K by means of 3-D classical trajectory technique. For this purpose stratified and importance sampling techniques were adopted to trajectory studies of dissociation. The dissociation cross-sections for I 2 –Ar reaction were computed between 1000 and 3500 K as a function of impact parameter and I 2 internal energy. It was found that for this reaction the overwhelming contribution to the overall rate coefficient comes from trajectories which involve I 2 molecules with initial internal energy ± 1 kT within the dissociation limit. For I 2 –Xe reaction at 300 K the ‘collisional release' mechanism contributes to dissociation and the ‘reactive’ I 2 have a broader energy range between –4 kT to + 1 kT within the dissociation limit. Highly excited metastable I 2 dissociate predominantly by de-excitation collisions in which the total as well as the rotational energy of the reactant molecule is decreased. The equilibrium dissociation rate coefficients (one-way fluxes) for I 2 –Ar system at 1000 and 1500 K, obtained in this work, are consistent with existing experimental rate constants. However, the temperature coefficient of recombination reaction, obtained from shock tube experiments, is more negative than present calculations appear to suggest.

Ab initio rate coefficients for reactions of 2,5-dimethylhexyl isomers with O2: temperature- and pressure-dependent branching ratios

2021 ◽  
Vol 23 (10) ◽  
pp. 6225-6240
Author(s):  
Mohamad Akbar Ali
Keyword(s):  
Ab Initio ◽  
Branching Ratios ◽  
Rate Coefficients ◽  
Temperature And Pressure

Pressures-dependence rate coefficients for the formation 2,2,5,5-tetramethyl-tetrahydrofuran.

scholarly journals Subauroral red arcs as a conjugate phenomenon: comparison of OV1-10 satellite data with numerical calculations

1997 ◽  
Vol 15 (8) ◽  
pp. 984-998 ◽  
Author(s):  
A. V. Pavlov
Keyword(s):  
Electron Density ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Atomic Oxygen ◽  
Major Ions ◽  
Integral Intensity ◽  
Rate Coefficients ◽  
Vibrationally Excited ◽  
Vibrational Distribution ◽  
Vibrational Levels

Abstract. This study compares the OV1-10 satellite measurements of the integral airglow intensities at 630 nm in the SAR arc regions observed in the northern and southern hemisphere as a conjugate phenomenon, with the model results obtained using the time-dependent one-dimensional mathematical model of the Earth ionosphere and plasmasphere (the IZMIRAN model) during the geomagnetic storm of the period 15–17 February 1967. The major enhancements to the IZMIRAN model developed in this study are the inclusion of He+ ions (three major ions: O+, H+, and He+, and three ion temperatures), the updated photochemistry and energy balance equations for ions and electrons, the diffusion of NO+ and O2+ ions and O(1D) and the revised electron cooling rates arising from their collisions with unexcited N2, O2 molecules and N2 molecules at the first vibrational level. The updated model includes the option to use the models of the Boltzmann or non-Boltzmann distributions of vibrationally excited molecular nitrogen. Deviations from the Boltzmann distribution for the first five vibrational levels of N2 were calculated. The calculated distribution is highly non-Boltzmann at vibrational levels v > 2 and leads to a decrease in the calculated electron density and integral intensity at 630 nm in the northern and southern hemispheres in comparison with the electron density and integral intensity calculated using the Boltzmann vibrational distribution of N2. It is found that the intensity at 630 nm is very sensitive to the oxygen number densities. Good agreement between the modelled and measured intensities is obtained provided that at all altitudes of the southern hemisphere a reduction of about factor 1.35 in MSIS-86 atomic oxygen densities is included in the IZMIRAN model with the non-Boltzmann vibrational distribution of N2. The effect of using of the O(1D) diffusion results in the decrease of 4–6% in the calculated integral intensity of the northern hemisphere and 7–13% in the calculated integral intensity of the southern hemisphere. It is found that the modelled intensities of the southern hemisphere are more sensitive to the assumed values of the rate coefficients of O+(4S) ions with the vibrationally excited nitrogen molecules and quenching of O+(2D) by atomic oxygen than the modelled intensities of the northern hemisphere.

scholarly journals The role of vibrationally excited oxygen and nitrogen in the ionosphere during the undisturbed and geomagnetic storm period of 6-12 April 1990

1998 ◽  
Vol 16 (5) ◽  
pp. 589-601 ◽  
Author(s):  
A. V. Pavlov
Keyword(s):  
Loss Rate ◽  
Boltzmann Distribution ◽  
Rate Coefficients ◽  
Ion Chemistry ◽  
Vibrationally Excited ◽  
Model Calculations ◽  
F Region ◽  
Neutral Temperature ◽  
The Difference ◽  
Excited Nitrogen

Abstract. We present a comparison of the observed behavior of the F-region ionosphere over Millstone Hill during the geomagnetically quiet and storm periods of 6–12 April 1990 with numerical model calculations from the IZMIRAN time-dependent mathematical model of the Earth's ionosphere and plasmasphere. The major enhancement to the IZMIRAN model developed in this study is the use of a new loss rate of O+(4S) ions as a result of new high-temperature flowing afterglow measurements of the rate coefficients K1 and K2 for the reactions of O+(4S) with N2 and O2. The deviations from the Boltzmann distribution for the first five vibrational levels of O2(v) were calculated, and the present study suggests that these deviations are not significant. It was found that the difference between the non-Boltzmann and Boltzmann distribution assumptions of O2(v) and the difference between ion and neutral temperature can lead to an increase of up to about 3 or a decrease of up to about 4 of the calculated NmF2 as a result of a respective increase or a decrease in K2. The IZMIRAN model reproduces major features of the data. We found that the inclusion of vibrationally excited N2(v > 0) and O2(v > 0) in the calculations improves the agreement between the calculated NmF2 and the data on 6, 9, and 10 April. However, both the daytime and nighttime densities are reproduced by the IZMIRAN model without the vibrationally excited nitrogen and oxygen on 8 and 11 April better than the IZMIRAN model with N2(v > 0) and O2(v > 0). This could be due to possible uncertainties in model neutral temperature and densities, EUV fluxes, rate coefficients, and the flow of ionization between the ionosphere and plasmasphere, and possible horizontal divergence of the flux of ionization above the station. Our calculations show that the increase in the O+ + N2 rate factor due to N2(v > 0) produces a 5-36 decrease in the calculated daytime peak density. The increase in the O++ O2 loss rate due to vibrational-ly excited O2 produces 8-46 reductions in NmF2. The effects of vibrationally excited O2 and N2 on Ne and Te are most pronounced during the daytime.Key words. Ion chemistry and composition · Ionosphere – atmosphere interactions · Ionospheric disturbances

scholarly journals The calculation of TV, VT, VV, VV' − rate coefficients for the collisions of the main atmospheric components

1998 ◽  
Vol 16 (7) ◽  
pp. 838-846 ◽  
Author(s):  
A. S. Kirillov
Keyword(s):  
Experimental Data ◽  
Energy Transfer ◽  
Vibrational Energy ◽  
Relaxation Times ◽  
Atmospheric Composition ◽  
Rate Coefficients ◽  
Frequency Change ◽  
Vibrational Energy Transfer ◽  
Ion Chemistry ◽  
Vibrationally Excited

Abstract. The first-order perturbation approximation is applied to calculate the rate coefficients of vibrational energy transfer in collisions involving vibrationally excited molecules in the absence of non-adiabatic transitions. The factors of molecular attraction, oscillator frequency change, anharmonicity, 3-dimensionality and quasiclassical motion have been taken into account in the approximation. The analytical expressions presented have been normalized on experimental data of VT-relaxation times in N2 and O2 to obtain the steric factors and the extent of repulsive exchange potentials in collisions N2-N2 and O2-O2. The approach was applied to calculate the rate coefficients of vibrational-vibrational energy transfer in the collisions N2-N2, O2-O2 and N2-O2. It is shown that there is good agreement between our calculations and experimental data for all cases of energy transfer considered.Key words. Ionosphere (Auroral ionosphere; ion chemistry and composition). Atmospheric composition and structure (Aciglow and aurora).

Theoretical investigation of the isomerization pathways of diazenes: torsion vs. inversion

2019 ◽  
Vol 21 (28) ◽  
pp. 15678-15685 ◽  
Author(s):  
Aarti Sindhu ◽  
Renuka Pradhan ◽  
Upakarasamy Lourderaj ◽  
Manikandan Paranjothy
Keyword(s):  
Ab Initio ◽  
Theoretical Investigation ◽  
Classical Trajectory ◽  
Centrifugal Barrier ◽  
Out Of Plane ◽  
Trajectory Simulations

Ab initio classical trajectory simulations show that diazenes isomerize via out-of-plane torsion and not in-plane inversion due to a centrifugal barrier.

scholarly journals The influence of pressure on the spontaneous ignition of inflammable gas-air mixtures - IV—methane-, ethane-, and propane-air mixtures

1936 ◽  
Vol 154 (881) ◽  
pp. 95-112 ◽  
Keyword(s):  
Critical Pressure ◽  
Spontaneous Ignition ◽  
Lower Range ◽  
Experimental Conditions ◽  
Temperature Range ◽  
Limited Temperature ◽  
Tentative Hypothesis ◽  
Temperature Ranges ◽  
Higher Temperature ◽  
Temperature And Pressure

In previous papers the results of investigations into the influence of varying initial pressures up to 15-20 atmospheres on the spontaneous ignition of mixtures with air of butane, iso -butane, pentane, and hexane were described. On the attainment of a critical pressure, which varied both with the hydrocarbon concerned and the composition of its mixture with air, the ignition points were always found to fall sharply from a higher temperature range above 500°C to a lower range at about 300°C. At pressures just exceeding the critical transition pressures ignition occurred at first only within limited temperature ranges which widened and ultimately merged with increasing pressure. The striking relationship between the behaviours of the hydrocarbons referred to under the experimental conditions and their “knocking” propensities in an engine was also indicated. While the data available were inadequate for drawing any final con­clusion as to the character of the phenomena referred to, a tentative hypothesis was advanced that while ignition in the higher temperature range pertains mainly to the thermal decomponents of intermedially formed compounds, ignition in the lower system occurs when temperature and pressure conditions favour the survival and further oxidation of such bodies, particularly aldehydes.

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