Knowledge Bank

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=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$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, 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$\mathrm{<mrow\; data-mjx-texclass="ORD">-5</mrow>}$ 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 .