Characterization of the ground and excited states of lanthanum oxide through bimolecular oxidation of La metal with O2, NO2, N2O, and O3

Using a beam–gas arrangement, we have studied the chemiluminescent emission which results when a thermal beam of La atoms (1750–2400 K) intersects a tenuous atmosphere (10−6 to 10−4 torr) of one of the thermal oxidants O2, NO2, N2O, or O3 (300 K). The La–O2 reaction is characterized by visible chemiluminescence from the B 2Σ+ and C 2Π states of LaO. The La–NO2, La–N2O, and La–O3 reactions are characterized by emission from the B 2Σ+, C 2Π, and D 2Σ+ states of LaO. In addition all four systems are characterized by extensive emission from the A 2Π state of LaO. From the chemiluminescent spectrum for the La–O2 system, a minimum value of 8.19±0.04 eV is deduced for the dissociation energy of lanthanum monoxide. This lower bound is in good agreement with previous mass spectrometric determinations (8.28±0.11 and 8.38±0.2 eV). We discuss the temperature dependence of the four chemiluminescent reactions deducing an upper bound for the heat of vaporization of lanthanum metal. We combine the results of our temperature dependent studies with reactant–product correlations and demonstrate the manner in which this blend can be used to elucidate the significance and dynamics of reaction of low lying atomic states in the oxidation reactions of high temperature metallic beams.