Quenching and energy transfer processes of single rotational levels of Br2 B 3Π(0+u) v′=24 with Ar under single collision conditions

Abstract

State-specific total quenching rate constants are measured for selected rotational levels of Br2 under single collision conditions with argon at 296 K. A strict criterion is used to obtain single collision conditions in a cell experiment. A 0.04 cm−1 bandwidth, etalon-narrowed pulsed dye laser excites single rovibronic transitions of the B 3Π(0+u) state, and fluorescence decay traces with and without the argon collision partner are analyzed at early times to extract total quenching rate constants. The rotational levels that are initially prepared are J′=26, 32, 37, 41, 46, and 58. The total quenching rate constants dramatically decrease with increasing J′: for J′=26/32/37/41, respectively, they are =8.7×10−11/4.4×10−11/3.3×10−11/7.6×10−12 cm3 molecule−1 s−1. The effect of rotational excitation on the quenching is interpreted to be due to the decreased probability of forming collision complexes. In contrast to the levels J′<41, negative quenching rate constants are observed for J′>41, i.e., the decay rates with Ar are slower than those without. This result can be explained by taking into account the possibility of R↔V energy transfer processes in which a high rotational level is transferred to a lower rotational state in the next higher vibration and the lower rotational state has a much slower spontaneous predissociation rate.