Reactions of Ca and Sr with CH3X and CF3X (X  Br, I). A laser-induced fluorescence study on nascent CaBr, SrBr, and SrI Original Research Article

Continuous-wave laser-induced fluorescence (LIF) spectra have been measured of nascent SrBr, SrI, and CaBr, formed in the reactions of Sr with CH3X and CF3X (X  Br,I), and of Ca with CH3Br and CF3Br. The bandhead spectra measured for the reactions involving Sr can be attributed to the formation of highly vibrationally excited SrX; for the reaction with CF3I vibrational bandheads up to ν″ = 42 in SrI are observed. The LIF spectra of CaBr formed in the reactions of Ca with CH3Br and CF3Br can be interpreted as a sum of a thermal and a nonthermal spectrum. These two types of spectra originate from the formation of CaBr inside the Ca oven and in the reaction region outside the oven, respectively. In all cases studied, the spectroscopic constants reported in the literature from studies at low t; values need only minor modifications in order to yield a satisfactory fit of the measured spectra, even though products were formed in highly excited vibrational states. The results are compared with those of other studies of reactions of alkaline earth metals with halogenated methanes. A comparison of the energy disposal into the alkaline earth monohalide product as a function of the average available energy is hampered because of the uncertainty of the latter. In the present study the available energy, which is the sum of the internal energy of the molecular reactant, the collision energy, and the bond energies involved, is consistently too low as to give a satisfactory fit of the alkaline earth monohalide bandhead spectrum. The relatively high fraction of the available energy disposed into vibration of the diatomic product is indicative of an early energy release, such as takes place in an electron jump model. The variation of the disposal into vibrational energy of the formed diatom among the various systems is attributed to a variation of the harpooning radius and its magnitude relative to the interatomic distance of the diatomic product.