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Ohio State University

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The fluorescence lifetimes of the \~{A} states of C$_3$, C$_3$-Ne and C$_3$-Ar have been measured under supersonic molecular beam conditions. To minimize possible collisional quenching, the lifetimes of all three species were measured at a distance of about 42 nozzle diameters from the orifice. For all the vibrational levels of the \~{A} state of the C$_3$ monomer, only J$^{\prime}$=1 lifetimes were recorded, using R(0) lines. The accuracy of the lifetimes obtained was estimated to be better than 3ns. General features of the lifetimes of the C$_3$ monomer are as follows: with increasing excitation of the symmetric stretching vibration, the lifetimes increase to a maximum at v$_1$=4. Bending excitation reduces the lifetimes, though exceptions occur for the 0 v 0 and 1 v 0 levels. Among all the vibrational levels, 0 2$^-$ 0, 0 4$^-$ 0, and 0 2$^+$ 0 have the shortest lifetimes, similar to that of the origin level . Lifetimes of the \~{A} state of C$_3$-Ne and C$_3$-Ar have only been measured for features 1.5-2 and 11-14 cm$^{-1}$, respectively, to the red of the R(0) lines of the \~{A}$-$\~{X} bands of free C$_3$. 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 1-2x10$^{-5}$ torr by lowering the repetition rate. No sign of predissociation was found in the Ne complex except for the level 0 12$^+$ 0. The lifetimes of the complexes did not vary with vibration in the manner found for C$_3$ itself. The lifetime of the 0 2$^-$ 0 level, one of the lowest vibrational levels of the \~{A} state, was not affected by complexing with either Ne or Ar, consistent with the observation that the least van der Waals shifts were observed for this vibrational level .


Author Institution: Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei 10617, Taiwan, R. O. C.