Temperature dependence of vibrational relaxation times in gases

1958 ◽  
Vol 244 (1237) ◽  
pp. 212-219 ◽  
Keyword(s):  
Energy Transfer ◽  
Methyl Bromide ◽  
Sulphur Dioxide ◽  
Vibrational Relaxation ◽  
Transition Probability ◽  
Relaxation Times ◽  
Methyl Chloride ◽  
Collision Theory ◽  
Ultrasonic Dispersion ◽  
Carbon Tetrafluoride

Ultrasonic dispersion measurements at varying temperatures, extending over the range 290 to 580° K, have been made on gaseous ethylene, cyclo propane, carbon tetrafluoride, methyl chloride and methyl bromide. The results are correlated with previous measurements on methyl fluoride and sulphur dioxide. The non-polar gases show a steady rise in the probability of energy transfer between translation and vibration with rise in temperature. The transition probability, P 10 , is found to vary with exp — T -½ in accordance with current collision theory, but the quantitative dependence cannot be predicted from molecular properties. The polar gases behave in a similar way at higher temperatures, but at lower temperatures the transition probability increases with falling temperature. This is interpreted as due to increasing predominance of oriented collisions, which are specially favourable for energy transfer, between polar molecules at lower temperatures.

Calculation of vibrational relaxation times in gaseous sulphur dioxide

1957 ◽  
Vol 243 (1232) ◽  
pp. 84-93 ◽  
Keyword(s):  
Specific Heat ◽  
Sulphur Dioxide ◽  
Vibrational Relaxation ◽  
Vibrational Excitation ◽  
Relaxation Times ◽  
Collision Theory ◽  
Relaxation Behaviour ◽  
Ultrasonic Dispersion ◽  
Higher Modes ◽  
Dispersion Data

Approximate vibrational relaxation times have been calculated for gaseous sulphur dioxide at 373°K using the collision theory of Schwartz & Herzfeld (1954). Two major effective relaxation times are found; the shorter associated with the relaxation of the specific heat contribution of the lowest mode and the longer with the relaxation of the total contributions of the two higher modes. The results are compared with the recent ultrasonic dispersion data of Lambert & Salter (1957), a measure of agreement being found. The mechanism of vibrational excitation in gaseous sulphur dioxide is discussed and compared with that in some similar molecules. Tentative predictions are made about the relaxation behaviour of a few selected molecules.

Energy transfer in polyatomic molecules. II. Relative catalytic efficiency for energy transfer to different vibrations to the same molecule

1961 ◽  
Vol 264 (1318) ◽  
pp. 299-308 ◽  
Keyword(s):  
Energy Transfer ◽  
Sulphur Dioxide ◽  
Deuterium Oxide ◽  
Relaxation Times ◽  
Catalytic Efficiency ◽  
Polyatomic Molecules ◽  
Fair Agreement ◽  
Water Molecules ◽  
Relaxation Processes ◽  
Ultrasonic Measurements

Vibrations of sulphur dioxide show two separate relaxation times. Values of r 1 = 6.0 × 10 -8 s for the vibrations of 519 cm -1 and r 2 = 1.2 × 10 -6 s for the vibrations of 1151 and 1361 cm -1 have been derived from new ultrasonic measurements, in fair agreement with earlier work. Molecules studied as possible vibration-translation catalysts included ethane, ethylene, water, and n -hexane. No enhanced efficiency of energy transfer was observed with ethylene. Ethane and water molecules were found to be only moderately efficient catalysts; proportionally, they exert a greater effect for processes associated with r 1 . Deuterium oxide is found to be somewhat more efficient than water. n -Hexane is highly efficient for both the r 1 and r 2 relaxation processes of sulphur dioxide. These observations are discussed in relation to various mechanisms for the catalysis of energy transfer.

The pressure dependence of refractivity of polar gases

1960 ◽  
Vol 255 (1282) ◽  
pp. 427-433 ◽  
Keyword(s):  
Pressure Dependence ◽  
Sulphur Dioxide ◽  
Experimental Error ◽  
Methyl Chloride ◽  
Molecular Polarizability ◽  
Refractive Indices ◽  
Methyl Fluoride ◽  
Carbon Tetrafluoride ◽  
First Order

The refractive indices of several gases have been measured at varying pressures in the range 0 to 50 cm. For carbon tetrafluoride, methyl fluoride and methyl chloride the refractivity varies directly with the density within the limits of experimental error. For ammonia and sulphur dioxide the increase of refractivity with pressure is less than would correspond to the increase in density. This may be interpreted in terms of a negative ‘first-order hyperpolarizability' for the polar vapours, whose molecular polarizability is being decreased by the influence of the field due to neighbouring molecular dipoles.

Analytic solution of relaxation and dissociation of ozone and sulphur dioxide at low pressures

1981 ◽  
Vol 59 (17) ◽  
pp. 2569-2574 ◽  
Author(s):  
Wendell Forst
Keyword(s):  
Rate Constants ◽  
Sulphur Dioxide ◽  
Vibrational Relaxation ◽  
Analytic Solution ◽  
Thermal Dissociation ◽  
Relaxation Times ◽  
Average Energy ◽  
Collision Rate ◽  
Low Pressures ◽  
Good Agreement

The analytic solution of vibrational relaxation in a low-pressure gas is applied to the thermal dissociation of O3 in helium and of SO2 in argon. Use is made of experimental relaxation times to obtain average energy lost per collision. Calculated weak-collision rate constants are in very good agreement with experiment in the case of SO2, but only in fair agreement in the case of ozone. Several curious aspects of the ozone system, both experimental and theoretical, are discussed.

The Master Equation for the Dissociation of a Dilute Diatomic Gas IX. Rotation–Vibration Relaxation Times

1973 ◽  
Vol 51 (12) ◽  
pp. 1923-1932 ◽  
Author(s):  
E. Kamaratos ◽  
H. O. Pritchard
Keyword(s):  
Shock Wave ◽  
Relaxation Time ◽  
Vibrational Relaxation ◽  
Transition Probabilities ◽  
Transition Probability ◽  
Relaxation Times ◽  
Rotational Relaxation ◽  
Relaxation Matrix ◽  
Coupling Case ◽  
Increasing Temperature

The relationships between individual rotational or vibrational transition probabilities and the eigenvalues of the 172nd order relaxation matrix describing the rotation–vibration–dissociation coupling of ortho-hydrogen are explored numerically. The simple proportionality between certain transition probabilities and certain eigenvalues, which was found previously in the vibration–dissociation coupling case, breaks down. However, it is shown that at 2000°K the second smallest eigenvalue of the relaxation matrix (dn−2), hitherto regarded as determining the "vibrational" relaxation time, is related more to the transition probability assigned to the largest rotational gap which lies in the first (ν = 0 ↔ ν = 1) vibrational gap, i.e. to the transition ν = 0, J = 5 ↔ ν = 0, J = 7, than to anything else; this clearly supports an earlier suggestion that the transient which immediately precedes dissociation in a shock wave has to be regarded as a rotation–vibration relaxation time rather than a vibrational relaxation time. It is suggested that the Lambert–Salter relationships can be rationalized on this assumption.An analysis is then made of the energy uptake associated with each eigenvalue at three temperatures. At 500°K, the greatest energy increment is associated with two eigenvalues (dn−13 and dn−24) and can be characterized as essentially a rotational relaxation: the calculations confirm that the observed rotational relaxation time should first decrease and then increase with increasing temperature, as was recently found to be the case experimentally. At 2000°K, large energy increments are associated with several eigenvalues between dn−2 and dn−14, and at 5000°K, with most of the eigenvalues dn−2 to dn−23; thus, the higher the temperature, the more complex is the (T–VR) rotation–vibration relaxation. Further, relaxation times for the same temperature measured by ultrasonic and shock-wave techniques need not agree.

Ultrasonic dispersion in gaseous sulphur dioxide

1957 ◽  
Vol 243 (1232) ◽  
pp. 78-83 ◽  
Keyword(s):  
Relaxation Time ◽  
Sulphur Dioxide ◽  
Major Part ◽  
Vibrational Energy ◽  
Vibrational Mode ◽  
Relaxation Times ◽  
Ultrasonic Waves ◽  
Ultrasonic Frequency ◽  
Ultrasonic Dispersion ◽  
Dispersion Zone

The velocity of ultrasonic waves has been measured in gaseous sulphur dioxide at 20, 102 and 200° C for values of f/p ranging from 200 kcs -1 atm -1 to 7 Mcs -1 atm -1 . ( f is the ultrasonic frequency, p the pressure.) Dispersion involving the major part of the vibrational specific heat was found at all temperatures. Each dispersion zone corresponds to two distinct relaxation times differing by a factor of ten. The lower relaxation time corresponds with activation of the lowest (519 cm -1 ) vibrational mode, the higher to activation of the remainder of the vibrational energy. The conditions giving rise to a double relaxation process are discussed.

Vibrational Energy Transfer in CHF3 -Mixtures

1976 ◽  
Vol 31 (10) ◽  
pp. 1268-1270 ◽  
Author(s):  
K. Frank ◽  
P. Hess
Keyword(s):  
Energy Transfer ◽  
Vibrational Relaxation ◽  
Vibrational Energy ◽  
Relaxation Times ◽  
Rare Gas ◽  
Vibrational Energy Transfer

Abstract The vibrational relaxation times for pure CHF, and CHF3 diluted in H2, D2, Ar, Kr and Xe are 0.55; 0.01, 0.025, 2.6, 4.8, and 5.6 /μsec atm at 298 K. These measurements complete previous results obtained for the systems CHF3-He, Ne, Ar. Correlation of the rare-gas results according to SSH-theory shows that relatively small rotational contributions may be expected for the heavy collision partners Kr and Xe.

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