Calculation of ion mobility in gas mixture

Dear experts

I want to calculate the ion mobility and make mobility file of He-isobutane mixture at 90:10, I found the He+ in He mobility in the paper I got here before (H.W.Ellis 4 series papers) and the ion mobility in pure isobutane (this is a little complicated since different ions are generated, I attach the paper here: )

I want to use the Blanc’s law to calculate, but

  • The ion mobility in pure isobutane is not for He+ but for much heavier ions
  • The pressure of that ion mobility experiment in pure isobutane is not 1atm but 8 Torr

so I wonder:

  • Can I just use Blanc’s law to calculate the mobility by using these two mobilities for different ions?
  • How can I convert the mobility from 8 Torr to 1atm value?

Maybe this is not a programing question…I’m not sure if I should ask here

Hi Siyuan,

Indeed, this question does not really seem related to ROOT.


Thank you for the reply! It’s actually related to Garfield++ since I want to make the ion mobility file to simulate the ion drift in gas.

I figured :slight_smile:

Blanc’s law gives a recipe for calculating the mobility of an ion species in a mixture, given the mobilities in the pure gases. In your case the situation is indeed a bit more difficult I’m afraid.

The mobility scales with the gas density. The values given in the Ellis et al. tables are reduced mobilities K0 = K * (p / p0) * (T0 / T), where p, T are the pressure and temperature in the gas, K is the mobility at this pressure and temperature, and p0 = 760 Torr, T0 = 273.16 K. The ion mobility files that you can load in Garfield++ are also based on the reduced mobility values.

Thank you for the answer! In my case the mixture of He and isobutane will generate different ions, and what I can find is C2H3+ in iC4H10, C4H10+ in iC4H10. But I think in the He-iC4H10 90:10 mixture almost all ions are He+, is there a way to calculate the He+ mobility in iC4H10 based on C2H3+ or something in iC4H10?

You might want to investigate which ion is responsible for the charge transport in He:iC4H10 mixtures, He+ might be subject to charge transfer in collisions with iC4H10 atoms. I think the article you attach is quite instructive on this item. I think it is not obvious to derive He:iC4H10 from the Ar:iC4H10 case. Best would be to reach out to colleagues in your field working with the He:iC4H10 mixture and performing ion drift velocity measurements. It would be good to compare MC simulations for signal shape to measured signals to validate the ion velocity you are using in simulation.

Thank you for the detailed explanation, and you are right that I better to make some experiment for the ion mobility in such kind of gas mixture.

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