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Rotational Cut-Off and Anharmonicity Effects on Thermodynamic Properties of Gases at High Temperatures

Published online by Cambridge University Press:  07 June 2016

N M Reddy
N M Reddy*
Affiliation:
Indian Institute of Science, Bangalore
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Summary

The exact expressions for the partition function Q and the coefficient of specific heat at constant volume Cv for a rotating-anharmonic oscillator molecule, including coupling and rotational cut-off, have been formulated and values of Q and Cv have been computed in the temperature range of 100°K to 100 000°K for O2, N2 and H2 gases. The exact Q and Cv values are also compared with the corresponding rigid-rotator harmonic-oscillator (infinite rotational and vibrational levels) and rigidrotator anharmonic-oscillator (infinite rotational levels) values. The rigid-rotator harmonic-oscillator approximation can be accepted for temperatures up to about 5000°K for O2 and N2. Beyond these temperatures the error in Cv will be significant, owing to anharmonicity and rotational cut-off effects. For H2, the rigid-rotator harmonic-oscillator approximation becomes unacceptable even for temperatures as low as 2000°K.

Type
Research Article
Information
Aeronautical Quarterly , Volume 25 , Issue 4 , November 1974 , pp. 287 - 292
Copyright
Copyright © Royal Aeronautical Society. 1974

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References

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