A classical functional sensitivity analysis of the collinear F+H ₂ reaction

The method of classical functional sensitivity analysis (CFSA) is applied to the collinear F + H₂ reaction and its isotopic analogues. The effects of features in the Muckerman 5 (M5) potential upon product vibrational energy are examined using constant energy ensembles (1 and 5 kcal/mol) with H₂(v = 0) and H₂(v = 1). The same is done using thermal averaged ensembles at 300, 400, 1000, and 1500 K. Two significant results are reported. First, at low energies and at even relatively high temperatures (1000 K), the region of the potential to which the reactive product vibrational energy is most sensitive is the vicinity of the saddle point. In addition, the sensitivity function is smooth and nonoscillatory there. Second, at high temperatures and energies, the sensitivity function becomes oscillatory in magnitude and sign over the entire interaction region. The implications which these results have for methods which fit a potential to experimental data are discussed.