AB-INITIO SIMULATION OF MOLECULAR-BEAM EXPERIMENTS FOR THE F-2-]HF+H REACTION(H)

The celebrated 1985 molecular beam measurements for the F + H-2 reacti on of Lee and co-workers, consisting of time-of-flight (TOF) spectra a nd angular distributions (AD) at several collision energies, have been directly simulated using fully resolved differential cross-sections ( DCS) obtained in accurate quantum mechanical (QM) and quasi-classical trajectory (QCT) calculations on the most recent ab initio potential e nergy surface (PES) by Stark and Werner. The simulations performed usi ng the QM calculations show an unprecedentedly good agreement with the experimental results for all final vibrational states of the HF produ ct. In particular, the height of the peak in the experimental laborato ry angular distribution corresponding to HF(upsilon'=3) forward scatte ring is quite well reproduced by the simulation using the QM theoretic al data at all three experimental collision energies for both para and normal hydrogen. The most important discrepancies between theory and experiment are found in the HF(upsilon'=3) sideways and backward scatt ering. The simulations carried out with the QCT data, although account ing correctly for the backward scattering, fail to account for most of the upsilon'=3 forward scattering. The analysis performed in this wor k indicates that an unbiased comparison between theoretical and experi mental results in the laboratory frame (as opposed to the center-of-ma ss frame) is required to assess the quality of a theoretical calculati on on a given ab initio PES.