## The ^{4}He^{+} ion population decay under different Ar pressures (a) and the corresponding decay rates plotted against Ar number densities (b)

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**Figure A4.** The ^{4}He^{+} ion population decay under different Ar pressures (a) and the corresponding decay rates plotted against Ar number densities (b). The rate coefficient from (b) is used to determine the ECIL rate coefficients of ^{3}He^{2 +}–N_{2} and ^{3}He^{2 +}–CO.

**Abstract**

We report our measured values for the sum of single and double charge transfer rate coefficients between ^{3}He^{2 +} and H_{2}, CH_{4}, N_{2} and CO. Our values are 2.4 ± 0.2 **×** 10^{−9} cm^{3} s^{−1} for H_{2}, 6.3 ± 0.9 **×** 10^{−9} cm^{3} s^{−1} for CH_{4}, 4.0 ± 0.3 **×** 10^{−9} cm^{3} s^{−1} for N_{2} and 4.7 ± 0.4 **×** 10^{−9} cm^{3} s^{−1} for CO. The values are obtained at equivalent temperatures of 1200–2400 K.