... gas

Draine & Salpeter (1979) give the following accurate approximations for n=0 and n=4:

$$G_0(\xi)\approx \frac{8}{3\sqrt{\pi}}\left(1+\frac{9\pi}{64}\... ...G_4(\xi)\approx \left(\frac{3\sqrt{\pi}}{4}+\xi^3\right)^{-1}.$$

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...1973)

The momentum transfer cross section measured in laboratory experiments is usually given as function of the energy in the laboratory frame ( $E_{\rm lab}$). Before using Eq. (19), $E_{\rm lab}$ must be converted into the energy in the center-of-mass frame according to the formula

$$E_{\rm cm}=\frac{m_s}{m_s+m_{s^\prime}}E_{\rm lab} +\frac{3m_{s^\prime}}{2(m_s+m_{s^\prime})}kT_s,$$

where s and $s^\prime$ indicate the target and incident particles, respectively.

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...

Our rate coefficient for zero drift velocity differs by $\sim$20% from the result by Flower (2000) who adopts an averaging over the particles kinetic energy slightly different from our Eq. (19).

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