Energy partitioning in the reaction 16O(1D)+H2 18O→16OH+18OH. IV. Microscopic probabilities for 16OH+18OH coincident pairs

Abstract

The reaction16O(1 D)+H2 18O→16OH(16 f)+18OH( 18 f) yields product molecules with internal [i.e., rotational (j), electronic (Ω), and vibrational (v)] levels 16 f and 18 f. The corresponding populations 16 P(16 f) and 18 P(18 f) are determined experimentally by photochemical preparation of reactants and detection of products after a 10 ns delay. Using this information, we predict the joint probabilities P(18 f,16 f) of observing the product pair simultaneously. For this purpose, we exploit that (a) summations of the less resolved joint vibrational probabilities P(18 v,16 v) over 18 v or 16 v yield exactly the observed vibrational populations 16 P(16 v) or 18 P(18 v), respectively; (b) a fraction of the nonvibrational energy of the (18 v,16 v) pair is released as rotational energy; and (c) the product molecules rotate with approximately opposite angular momenta 16 j≊−18 j due to the kinematics of light atom transfer. Imposing the constraints (a)–(c), information theory is used to determine P(18 f,16 f) such that the summations over 18 f or 16 f yield optimal agreement with the experimental 16 P(16 f) or 18 P(18 f), respectively. The results show that (a) simultaneous vibrational excitation of the product pair is negligible, i.e., vibrational energy release is very specific; (c) specific rotational energy release increases with vibrational excitation; and (c) the internal distribution of vibrationally excited OH radicals also contributes to the internal distributions of their v = 0 partners.