scholarly journals Modeling the Vibrational Relaxation of Polyatomic Molecules. The Methylfluoride Case Study

1990 ◽  
Vol 10 (3) ◽  
pp. 147-158
Author(s):  
V. Tosa ◽  
R. Bruzzese ◽  
C. de Lisio ◽  
S. Solimeno
Keyword(s):  
Relaxation Time ◽  
Relaxation Process ◽  
Vibrational Relaxation ◽  
Vibrational Energy ◽  
Polyatomic Molecules ◽  
Rate Equations ◽  
Strongly Nonlinear ◽  
Nonlinear Character ◽  
Intermediate Size

We present in this paper a theoretical analysis of the vibrational translational (V-T) relaxation process in CH3F, carried out by using a numerical model based on rate equations. In particular, we have analysed the dependence of the V-T relaxation time on the average vibrational energy absorbed per molecule. We have also investigated the influence of the dependence of the rate constants used in the model, on the gas translational temperature. The results of the model clearly outline the strongly nonlinear character of the V-T relaxation process in CH3F, a situation commonly observed in other important polyatomic molecules of intermediate size each as SF6, freons, and related methylhalides.

Vibrational relaxation in gases

1959 ◽  
Vol 253 (1273) ◽  
pp. 277-288 ◽  
Keyword(s):  
Energy Transfer ◽  
Relaxation Process ◽  
Vibrational Relaxation ◽  
Vibrational Energy ◽  
Ultrasonic Waves ◽  
The Other ◽  
Ultrasonic Frequency ◽  
Hydrogen Atoms ◽  
Torsional Mode ◽  
Fundamental Frequencies

The velocity of ultrasonic waves has been measured in a number of gases at 25°C and for values of the ratio, ultrasonic frequency/pressure, ranging from 2 x 10 5 to 2 x 10 7 c s -1 atm -1 . Dispersion, corresponding to a single vibrational relaxation process was shown by acetylene, CD 3 Br and hexafluoro-ethane; and, to a double relaxation process, by ethane. Incipient dispersion was shown by propane, ethyl chloride, ethyl fluoride and dimethyl ether. No dispersion was shown by 1.1-difluoro-ethane, n -butane, iso -butane, neo -pentane and ammonia. Correlation of these with previous results leads to the conclusion that: ( а ) For molecules with a distribution of fundamental frequencies, such that there is only a small gap between the lowest and the remaining frequencies, vibrational activation enters via the lowest mode and spreads rapidly to the other modes, giving rise to a single relaxation process involving the whole of the vibrational energy. The chief factors determining the probability of excitation of the lowest mode are its frequency and the presence or absence of hydrogen atoms in the molecule. Molecules containing two or more hydrogen atoms suffer translational-vibrational energy transfer very much more easily than other molecules. Deuterium has almost the same effect as hydrogen. ( b ) For molecules, in which there is a large gap between the lowest and the remaining fundamental frequencies, a double relaxation process occurs. The complex energy transfer probabilities involved do not fit the same quantitative functional relation with vibrational frequency as in ( a ) above. ( c ) Torsional oscillations due to hindered internal rotation behave similarly to other fundamental modes. For molecules in which there is a large gap between the torsional frequency and the other modes (e. g. ethane) a double relaxation process occurs as in ( b ). Where there is no such gap, vibrational energy enters all modes via the torsional mode as in ( a ).

scholarly journals Vibrational Relaxation Process of Polyatomic Molecules Adsorbed in Zeolites

1999 ◽  
Vol 19 (1-4) ◽  
pp. 321-324 ◽  
Author(s):  
Ken Onda ◽  
Michio Yaginuma ◽  
Akihide Wada ◽  
Kazunari Domen ◽  
Chiaki Hirose
Keyword(s):  
Temperature Dependence ◽  
Relaxation Process ◽  
Vibrational Relaxation ◽  
Metal Carbonyl ◽  
Laser Pulses ◽  
Infrared Laser ◽  
Polyatomic Molecules ◽  
Vibrational Modes ◽  
Pump Probe ◽  
Zeolite Surface

The vibrational relaxation lifetimes of the CO stretching mode of Cr(CO)6 and Mo(CO)6 adsorbed in the cage of the HY, DY and NaY-type zeolites were measured at various temperature by pump-probe method using picosecond infrared laser pulses. It was shown by comparing the lifetimes that the accepting modes include both the vibrational modes of the metal carbonyl and those associated with the cations on the zeolite surface. The analysis of the temperature dependence of the lifetimes revealed that the number of the excited accepting modes are four with their energy lying around 500 cm-1.

Vibrational Energy Transfer in Silane and Silane Mixtures

1976 ◽  
Vol 31 (10) ◽  
pp. 1203-1209 ◽  
Author(s):  
Willi Janiesch ◽  
Helmut Ulrich ◽  
Peter Hess
Keyword(s):  
Experimental Data ◽  
Energy Transfer ◽  
Relaxation Time ◽  
Vibrational Relaxation ◽  
Energy Exchange ◽  
Vibrational Energy ◽  
Vibrational Energy Transfer

Abstract The vibrational relaxation time for pure SiH4 is 0.10, 0.083 and 0.072 μsec atm (±30%) at 295 K, 375 K and 462 K. For SiH4 diluted in He, D2 and H2 the corresponding numbers are 0.16, 0.081 and 0.031 μsec atm (± 30%) at 295 K. The binary two-level theory has been used to deter-mine the four V -R, T rates in the system SiH4 -CH4, and the rate for V-V exchange between SiH4 and CH4 from experimental data. From the Schwartz-Slawsky-Herzfeld-formula for V -T and V -V, T processes an equation is derived describing V -R and V -V, R energy exchange. The different models are compared with experimental data, especially with those found for the system SiH4 -CH4.

The Master Equation for the Dissociation of a Dilute Diatomic Gas. XI. Vibrational Freezing in a Nozzle Flow

1974 ◽  
Vol 52 (6) ◽  
pp. 939-941 ◽  
Author(s):  
Nabil I. Labib ◽  
Huw O. Pritchard
Keyword(s):  
Relaxation Time ◽  
Energy Level ◽  
Master Equation ◽  
Rate Constant ◽  
Ground State ◽  
Vibrational Relaxation ◽  
Vibrational Energy ◽  
Nozzle Flow ◽  
Vibrational Energy Level ◽  
Diatomic Gas

A previously reported calculation on a model expansion in a nozzle flow is extended to the point where the whole vibrational energy "freezes" and the behavior of the vibrational relaxation time is examined. Starting with the high levels, each individual vibrational energy level becomes decoupled from the ground state in sequence, down to and including υ = 1; under these conditions, all measures of the vibrational relaxation time fail, but perhaps surprisingly the rate constant for recombination remains well defined.

scholarly journals Thermodynamic Analysis of Relaxation Model for Non-Equilibrium Phase Behavior of Hydrocarbon Mixtures

2021 ◽  
Vol 2090 (1) ◽  
pp. 012138
Author(s):  
I M Indrupskiy ◽  
P A Chageeva
Keyword(s):  
Relaxation Time ◽  
Phase Behavior ◽  
Relaxation Process ◽  
Thermodynamic Analysis ◽  
Balance Equation ◽  
Equilibrium Phase ◽  
Characteristic Relaxation Time ◽  
Relaxation Model ◽  
Entropy Balance ◽  
Non Equilibrium

Abstract Mathematical models of phase behavior are widely used to describe multiphase oil and gas-condensate systems during hydrocarbon recovery from natural petroleum reservoirs. Previously a non-equilibrium phase behavior model was proposed as an extension over generally adopted equilibrium models. It is based on relaxation of component chemical potentials difference between phases and provides accurate calculations in some typical situations when non-instantaneous changing of phase fractions and compositions in response to variations of pressure or total composition is to be considered. In this paper we present a thermodynamic analysis of the relaxation model. General equations of non-equilibrium thermodynamics for multiphase flows in porous media are considered, and reduced entropy balance equation for the relaxation process is obtained. Isotropic relaxation process is simulated for a real multicomponent hydrocarbon system with different values of characteristic relaxation time using the non-equilibrium model implemented in the PVT Designer module of the RFD tNavigator simulation software. The results are processed with a special algorithm implemented in Matlab to calculate graphs of the total entropy time derivative and its constituents in the entropy balance equation. It is shown that the constituents have different signs, and the greatest influence on the entropy is associated with the interphase flow of the major component of the mixture and the change of the total system volume in the isotropic process. The characteristic relaxation time affects the rate at which the entropy is approaching its maximum value.

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