YI-JEN WANG, CHIAO-WEI CHEN, LIUZHU ZHOU, ANTHONY J. MERER, YEN-CHU HSU, Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei 10617, Taiwan, R. O. C..
Fluorescence lifetimes have been measured for 66 u and 16 +u vibronic levels of the A1 u state of C3 under nearly collision-free conditions. The vibrational levels studied were v1=0-5, v2=0-22, and v3=0-4, covering the energy range up to 6000 cm-1, and for most of them only the R(0) line was investigated. The measurements are estimated to be accurate to better than \pm3 ns. General features of the lifetimes are as follows: Pure bending levels with u-symmetry have shorter lifetimes (as short as 190 ns). With increasing excitation of the stretching vibrations, the lifetimes increase. Bending excitation generally reduces the lifetimes, though exceptions occur for v1=1. Levels with v1+v3 \geq 3 or with vibrational energy greater than 4000 cm-1 have lifetimes longer than 300 ns; some of these levels even have a long-lived component with a lifetime of up to several microseconds. This implies that the predicted dark states, (B1 u- and B' 1 u), lie at least 4000 cm-1 above the 0 0 0 level of the A state. It is interesting to note that most of the u+-symmetry levels lying above 4000 cm-1 also have lifetimes longer than 300 ns.