We have performed translational-spectroscopical measurements on single electron capture (SEC) by impact of slow (impact energy <= 1 keV) doubly charged ions on dinuclear molecules. For impact of C2+ and N2+ ions the influence of their metastable fractions on the SEC probability has been studied. For impact of He-4(2+) on O-2 and CO direct and dissociative SEC have been investigated. For all collision systems studied the principal SEC channels can be explained by the "reaction window" which results from multichannel-Landau-Zener treatments for the collisional quasimolecules.