LIFETIMES OF THE $\tilde{A}$ STATES OF THE C$_3$-NE AND C$_3$-AR COMPLEXES

Author Institution: Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei 10617, Taiwan, R. O. C.Under similar experimental conditions to our previous paper, the fluorescence lifetimes of the $\tilde{A}$ states of C$_3$-Ne and C$_3$-Ar have been determined. The uncertainties in the measured lifetimes are estimated to be better than 10\%. About 50 perpendicular bands and 11 parallel bands of the $\tilde{A}-\tilde{X}$ system of C$_3$ were used to probe the fluorescence lifetimes of the Ne and Ar complexes. It is not possible to reduce the backing pressure while measuring lifetimes of the complexes; we therefore reduced the average pressure of the chamber to 1$-$2 $\times$ 10$^{-5}$ torr by lowering the repetition rate. No sign of predissociation was found in either complex. Transitions to high vibrational levels of the $\tilde{A}$ state of C$_3$, above 4500 cm$^{-1}$, give weak laser-induced fluorescence signals, so that lifetime measurements are not possible for some of these bands. The lifetimes of the levels of the Ne complex lying below 4300 cm$^{-1}$ are generally shorter than 300 ns, except for some levels with C-C stretch excitation. The lifetimes of the Ne complex behave quite similarly to those of C$_3$. In contrast, the lifetimes of the Ar complex do not follow the vibrational dependence of the lifetimes of C$_3$ and C$_3$-Ne. We speculate that the complicated lifetime pattern observed in the Ar complex can be attributed to interactions with nearby triplet levels