REACTIONS OF CA AND SR WITH CH(3)X AND CF(3)X (X=BR,I) - A LASER-INDUCED FLUORESCENCE STUDY ON NASCENT CABR, SRBR, AND SRI

Continuous-wave laser-induced fluorescence (LIF) spectra have been mea sured of nascent SrBr, Sri, and CaBr, formed in the reactions of Sr wi th CH(3)X and CF(3)X (X = Br,I), and of Ca with CH3Br and CF3Br. The b andhead spectra measured for the reactions involving Sr can be attribu ted to the formation of highly vibrationally excited SrX; for the reac tion with CSI vibrational bandheads up to v '' = 42 in SrI are observe d. The LIF spectra of CaBr formed in the reactions of Ca with CH3Br an d CF3Br can be interpreted as a sum of a thermal and a nonthermal spec trum. These two types of spectra originate from the formation of CaBr inside the Ca oven and in the reaction region outside the oven, respec tively. In all cases studied, the spectroscopic constants reported in the literature from studies at low v values need only minor modificati ons 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 alka line earth metals with halogenated methanes. A comparison of the energ y disposal into the alkaline earth monohalide product as a function of the average available energy is hampered because of the uncertainty o f the latter. In the present study the available energy, which is the sum of the internal energy of the molecular reactant, the collision en ergy, and the bond energies involved, is consistently too low as to gi ve a satisfactory fit of the alkaline earth monohalide bandhead spectr um. The relatively high fraction of the available energy disposed into vibration of the diatomic product is indicative of an early energy re lease, such as takes place in an electron-jump model. The variation of the disposal into vibrational energy of the formed diatom among the v arious systems is attributed to a variation of the harpooning radius a nd its magnitude relative to the interatomic distance of the diatomic product.