Recent experimental results on the muon exchange from muonic hydrogen to argon show that the reaction rate is energy dependent near 0.1 eV. A muonic hydrogen atom, formed by muon capture in H{sub 2} gas at 15 bars, is thermalized in a few hundreds of nanoseconds. If the muon transfer reaction occurs before that time, the rate is shown to be slightly lower compared to thermalized muonic atoms [{lambda}{sub pAr}=(1.63{plus_minus}0.09){times}10{sup 11} s{sup {minus}1}]. As an indirect consequence, the muon transfer rate from {mu}p to helium, determined by our group [R. Jacot-Guillarmod and co-workers, Phys. Rev. A {bold 38}, 6151 (1988)] is lowered by about 40{percent}. The present value {lambda}{sub pHe}=(0.51{plus_minus}0.19){times}10{sup 8} s{sup {minus}1} is in good agreement with other experiments. The transfer rate from muonic deuterium to argon shows also an energy dependence. The muon transfer rate to argon from the deuteron is {lambda}{sub dAr}=(0.86{plus_minus}0.04){times}10{sup 11} s{sup {minus}1} at room temperature. The intensity patterns of the muonic Lyman series of argon obtained by muon transfer from both hydrogen isotopes are determined and compared with theoretical predictions. {copyright} {ital 1997} {ital The American Physical Society}