Abstract
The role of electron transfer (ET) is crucial in determining the fate of chemical reactions within a diversity of scientific domains, encompassing fundamental and applied research. In such processes where anion formation prevails, the rather complex mechanisms occurring at the molecular level still pose challenges to both experimentalists and theoreticians. Here, we address negative ion formation from crossed molecular beam experiments in a wide collision energy range, from a threshold up to a few keV, noting important aspects of the collision dynamics. This Perspective is not intended to give a review on electron transfer and negative ion formation but the authors' major contributions in atom-molecule and anion-molecule collision experiments, while also highlighting the most relevant achievements and challenges in some dedicated research fields that are still impacting many researchers across the globe.