The ORNL ion-atom merged-beams apparatus has measured benchmark electron capture cross sections for the multicharged ions Si⁴⁺ on D from 0.016 eV/u to 451 eV/u (Marc Pieksma, M. Gargaud, R. McCarroll, and C. C. Havener, Physical Review A, 54R13 (1996). State-of-the-art molecular-orbital coupled-channel calculations for the Si⁴⁺ + H(D) systems are compared to the measurements on an absolute scale. Both the existence of a surprisingly large kinematic isotope effect and an observed sharp low-energy increase of the cross section are attributed to trajectory effects due to an attractive ion-induced dipole.