Collisional dynamics of the BrCl B 3Π(0+) state. II. Vibrational and rotational energy transfer

Abstract

Vibrational and rotational energy transfer within the B 3Π(0+) state of bromine monochloride was studied using both pulsed and steady-state laser-induced fluorescence techniques. Rate coefficients for state-to-state vibrational transfer were determined from the observed BrCl(B–X) emission in the presence of Cl2, He, Ne, Ar, Kr, and Xe. Vibrational states v′=0 to 7 were probed, and resolved emission was observed from states v′=0 to 6. The vibrational transfer within BrCl(B) is rapid, as expected from the small vibrational spacing. The fundamental rate coefficient for vibrational transfer from v′=1 to v′=0 with chlorine as the collision partner is 1.3×10−11 cm3 molecules−1 s−1 and the vibrational transfer rate coefficient scales with vibrational quantum number as a power law with an exponent of 0.63. Vibrational transfer with the noble gases is less efficient with fundamental rate coefficients ranging from 4×10−12 cm3 molecules−1 s−1 for helium to 2×10−12 cm3 molecules−1 s−1 for krypton. The scaling of vibrational transfer rates with vibrational quantum number for the noble gases is consistent with the Landau–Teller theory. The Δv=−2 rate coefficients are estimated at 40% of the Δv=−1 rates. Methods of analyzing the temporal profiles of vibrationally resolved emission from laser-induced fluorescence experiments are described for conditions where vibrational transfer is rapid and the excited vibrational states are strongly coupled. Rotational transfer in BrCl(B) is very efficient with total removal rates ranging from 1.6×10−10 cm3 molecules−1 s−1 for chlorine collisions to 2.4×10−10 cm3 molecules−1 s−1 for argon.