The C1Πu-X1Σg+ fluorescence of Li2 excited by ultraviolet lines of an argon ion laser

The fluorescence spectra of ⁷Li₂ and ⁶Li₂ excited by an argon ion (3511 Å) laser are analyzed. No fluorescence was observed for 3514- or 3638-Å excitation or for ⁶Li⁷Li. For the C¹Π_u-X¹Σ_g⁺ electronic transition, the spectrum of ⁷Li₂ shows R and P doublets for 0 ≤ v″ ≤ 6 and that of ⁶Li₂ consists of Q lines for 0 ≤ v″ ≤ 11. Through the assignments of these lines (a) Hsu's (Ph.D. thesis, Fordham University, 1974, unpublished) molecular constants for C state have been verified, (b) the reliability of C- and X-state constants for ⁶Li₂ derived from those of ⁷Li₂ through mass-reduced scaling has been verified, and (c) the transition moment for the C-X transition of Li₂ has been shown by comparison of the observed and calculated intensities to be roughly independent of internuclear distance in the region near R_e for the C state.