Production efficiencies of electronically excited states of barium monohalides

Abstract

Diatomic barium monohalides (BaX) have been produced in the gas−phase reaction of Ba, entrained in a flowing inert carrier gas, with F2, SF6, Cl2, Br2, and I2. Bright green chemiluminescent flames were observed at pressures from 0.1−10 torr. Emission spectra were obtained from 300−1200 nm. Near infrared emission from BaBr and BaI has been ascribed to transitions to the ground state from previously unobserved electronic states analogous to A and B states in BaF and BaCl. In BaBr, electronic state energies for B 2Σ+, A 2Π3/2, and A 2Π1/2 have been found to be 11 325, 10 604, and 9980 cm−1, respectively; in BaI, corresponding values are 10 417, 9921, and 9268 cm−1. BaX molecules are produced with moderate efficiency into lower lying electronic states (80%−98% in A and B) with an absolute efficiency of approximately 1 photon for each 100 reacted barium atoms. There is a small dependence on pressure with maximum yields occuring near 4 torr. Spectra of C 2Π−X 2Σ+ transitions show Boltzmann distributions in both vibration and rotation corresponding to population temperatures of approximately 3000 K for BaF and 2000 K for BaBr, BaCl, and BaI. Electronic population temperatures show trends similar to those observed in vibration and rotation.