F-D2 state resolved reactive scattering at 180 and 240 meV collision energies. I. A high resolution crossed molecular beam experiment Original Research Article

The F + D2(ji) → DF(νf,jf) +D reaction has been studied in a high resolution crossed molecular beam scattering experiment at collision energies of 180 meV (4.1 kcal/mol) and 240 meV (5.5 kcal/mol), the highest collision energies ever achieved for this system in this kind of experiments. The product energy resolution in the time-of-flight (TOF) spectra was typically 30 meV and 35 meV, respectively. The vibrationally resolved center-of-mass (CM) differential cross sections (DCS) have been extracted from the TOF measurements and the productsʹ angular distributions (AD) in the laboratory (LAB) frame. It has been found that, for almost all the final states, the DCS shifts towards lower CM scattering angles as the collision energy increases. At the two collision energies studied, the scattering from the highest vibrational state accessible for the DF, i.e. νf = 4, gives rise to a prominent forward peak in the DCS that seems to increase as the collision energy goes up. Measurements carried out with D2 molecular beams at different rotational temperatures indicate that the large angle (backward) scattering increases with the initial rotation of the D2, in qualitative agreement with theoretical predictions. The rovibrationally state resolved integral reaction cross sections have been also experimentally deduced. All these results are compared with quasi-classical trajectory (QCT) calculations reported in the following paper of this issue.