EFFECT OF REAGENT VIBRATION ON PRODUCT ROTATION IN THE EXOTHERMIC REACTION BARIUM + HYDROGEN-FLUORIDE ---\u3e BARIUM-FLUORIDE + HYDROGEN (MOLECULAR, BEAM, DYNAMICS)

The exothermic reaction between Ba + HF (---\u3e) BaF + H has been studied as as function of reagent vibration. Rotational distributions of the product molecules are reported. The reaction takes place in a unique dual molecular beam apparatus designed to compare simultaneously BaF products formed from Ba + HF(v = 0) with those formed from Ba + HF(v = 1). An HF chemical laser excites HF molecules to v = 1. The BaF products are probed by Laser Induced Fluorescence. Through computer simulations of the LIF excitation spectral the rotational distributions are determined. The laser bandwidth was narrow enough ((DELTA)(lamda) = .25 cm(\u27-1)) to see rotational features which could be assigned (by computer simulation) to P(,12) lines of the low vibrational levels. By adjusting the upper state rotational constant so that the simulated features resembled the experimental features a value of (B(,e)(\u27(1)))(,eff) = .21397 cm(\u27-1) was obtained. The simulations incorporated a rotational distribution which gives a linear rotational surprisal. This distribution contains a temperature-like parameter, (theta)(,R)(\u27V). By iteratively fitting the simulated BaF spectra to their experimental counterparts, (theta)(,R)(\u27V)values were obtained for v = 0 and v = 1 reagents. For the Ba + HF(v = 0) reaction, the lowest five product vibrational levels contained approximately the same average rotational energy. For Ba + HF( v = 1) the best agreement between computer and experiment was obtained by choosing (theta)(,R)(\u27V) values which gave the same rotational distributions as the ground state reaction. It was thus seen that the rotational distributions appear to be independent of reagent vibration. An explanation of this result comes from treating the kinematics of the mass combination H + HL (---\u3e) HH + L (H = heavy, L = light). The product rotational quantum number J\u27 is determined by L the reagent orbital angular momentum, i.e., J\u27(TURN)L. Increasing the reagent vibration does not change L causing the rotational distributions to be independent of reagent vibration