Effect of Temperature in Gas Electron Diffraction. III. The Temperature Dependence of the First Four Moments of a Morse Oscillator

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Abstract
The effect of temperature on the first four moments of a Morse oscillator is investigated over the temperature range of 10°–1500°K. Numerical calculations are carried out for parameters of the I2 molecule. An expression of the Morse oscillator in a power series of the displacement coordinate is used to calculate the moments by both a variational and a perturbational approach. A classical calculation is also carried out for comparison. It is concluded that a potential with quadratic, cubic, and quartic terms can yield moments at about the 1% accuracy level up to 800°K, while that including the fifth‐ and sixth‐power terms yields moments at the same accuracy level up to 1000°K. Applications of results to gas electron diffraction are discussed.