The adiabatic electron affinities of several boron trihalides have been measured from the determination of threshold kinetic energies for the reaction Cs + BX3 + C s ' + BX). A crossed-molecular-beam apparatus was used. The electron affinities are

A crossed-beam system of Cs atoms and HNO3 molecules has been used to study the ion chemistry of HNO3. The existence of an HNO2− anion was observed and EA(HNO3) and D(H–ONO2−), the electron affinity of HNO3, and the dissociation energy of the parent anion were measured. Also, value for EA(NO3) was deduced which requires additional thermodynamic data and compare it with previous work. (AIP)

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Laser-induced predissociative fluorescence is often used for diagnostics because its short-lived upper states are minimally disturbed by collisions. We discuss the effects of lower-state collisions with parameters relevant to our atmospheric H(2)-O(2) flame. A pulse of tunable KrF excimer-laser light induces the A ? X, Q(1)(11), 3 ? 0 transition in OH. We measure the intensity and the polarization of the resulting A ? X, Q(1)(11), 3 ? 2 fluorescence as a function of laser brightness. A simple model that uses no adjustable parameters produces a reasonable fit to the data. It predicts that, even at very modest laser energies, the fluorescence intensity is almost directly proportional to the rate constant for rotational energy transfer (RET) within the lower vibrational state. That rate constant can be a strong function of local conditions. Furthermore, under typical operating conditions the excimer will pump an amount of OH out of the lower state that is many times as large as that originally present. This occurs because RET within the X-state continuously replenishes the lower state during the laser pulse. Even when this occurs, the signal may still vary linearly with laser intensity, and the polarization may be nearly that expected for weak pumping. At the higher laser intensities, a significant fraction of the measured OH arises from two-photon photodissociation of the water from the flame reaction.

The yttrium oxide emission produced in the photoablation of Y203, YCls, and YBazCu307-x in oxygen is investigated. Chemiluminescence from the B 22-X28 and the Ld 'II-X "L: YO electronic states, produced by the reaction Y +02, is measured. The intensity of the A 2113,2 band is monitored as a function of pressure, distance from the target, and laser fluence. Hydrodynamic effects have a significant influence on the spatial and temporal evolution of the YO emission in the plume, which is governed by the dynamics of the shock wave generated in the excimer ablation. This shock wave compresses the ambient oxygen and leaves a trough of rarefied oxygen in its wake. 7810