Laser-induced-fluorescence spectroscopy of jet-cooled C3

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Abstract
We present a spectroscopic study of jet‐cooled C3 in which laser‐induced‐fluorescence (LIF) excitation spectra and dispersed‐fluorescence (DF) spectra are taken for a new, vibronically induced band system (1Πg and/or 1Δu)−X̃ 1Σ+g in the ultraviolet. In addition, DF spectra are taken for the well‐known cometary band system, Ã 1Πu–X̃ 1Σ+g. The DF spectra of the new system are very rich and display strong fluorescence bands in stretch–bend progressions that reach as high as 17 000 cm−1 in the 1Σ+g ground state. The data from the DF spectra of both systems is used to assign vibrational term energies to 144 ground‐state levels that cover the range: 0≤v1≤8, 0≤v2≤37, and 0≤v3≤4. The observed level structure clearly demonstrates the highly anharmonic nature of the potential energy surface of C3 and the unusual internal dynamics that occurs upon it. These include pronounced barriers to linearity in the v3=2 and v3=4 states and an increase in molecular rigidity as the symmetric stretch is excited.